The friction stir welding (FSW) process was recently developed to overcome the difficulty of welding non-ferrous alloys and steels. In this study, dissimilar butt joints between 6061-T6 aluminum alloy and AISI 316 stainless steel were welded by FSW using different processing parameters. The grain structure and precipitates at the different welded zones of the various joints were intensively characterized by the electron backscattering diffraction technique (EBSD). Subsequently, the FSWed joints were tensile tested to examine the mechanical strength compared with that of the base metals. The micro-indentation hardness measurements were conducted to reveal the mechanical responses of the different zones in the joint. The EBSD results of the microstructural evolution showed that a significant continuous dynamic recrystallization (CDRX) occurred in the stir zone (SZ) of the Al side, which was mainly composed of the weak metal, Al, and fragmentations of the steel. However, the steel underwent severe deformation and discontinuous dynamic recrystallization (DDRX). The FSW rotation speed increased the ultimate tensile strength (UTS) from 126 MPa at a rotation speed of 300 RPM to 162 MPa at a rotation speed of 500 RPM. The tensile failure occurred at the SZ on the Al side for all specimens. The impact of the microstructure change in the FSW zones was significantly pronounced in the micro-indentation hardness measurements. This was presumably attributed to the promotion of various strengthening mechanisms, such as grain refinement due to DRX (CDRX or DDRX), the appearance of intermetallic compounds, and strain hardening. The aluminum side underwent recrystallization as a result of the heat input in the SZ, but the stainless steel side did not experience recrystallization due to inadequate heat input, resulting in grain deformation instead. Friction stir welding (FSW) is a green welding technology with high quality and low cost. The FSW process uses a non-consumable rotating tool with a designed shoulder and pin inserted into a butting edge or overlapped sheets or plates to be joined and traversed along the line of the joint ,2,3,4,5.2Al5, FeAl2, FeAl, and Fe3Al easily form at the weld interface. The IMCs result in the poor strength of the welded joints [The welding of aluminum to steel remains an enormous challenge. Due to the large differences in physical and mechanical properties between the two metals, producing a sound joint of aluminum and steel with high strength has been difficult. The solubility of iron (Fe) in the Aluminum (Al) matrix is limited, and the formation of brittle intermetallic compounds (IMCs) is a serious problem. From previous literature, and from the analysis of the binary phase diagram of Al–Fe, it has been reported that during the welding of aluminum alloy and steel, brittle IMCs of Fed joints ,20,21,22From the open literature, FSW of Al with CS has been reported in several publications. For instance, Abbasi et al.  studied The joint properties of dissimilar FSWed mild steel to A7075-T6 aluminum alloy were investigated by Tanaka et al. . The joi6Fe and Al5Fe2 in the joints. They noticed that by increasing the welding speed, the IMCs decreased and the joints exhibited higher tensile strength. Campanella et al. [5Fe2 during FSW of Al 3003-H18 to mild steel, while Al6 IMC was found in the weld nugget as scattered particles. The researchers obtained defect-free butt joints. The UTS of the joint increased to ~60% of that of the Al BM.Elrefaey et al.  successfa et al.  studied a et al.  successfa et al.  successfa et al.  studied a et al. , a conti2, FeAl3, Fe2Al5, and Fe3Al.Regarding the combination of aluminum and high-strength steel, this issue has been explored in some studies ,39,40,413, Fe2Al5, FeAl, Fe4Al13, Fe3Al, and Fe2AlCr IMCs, as well as SS fragments, was observed at the nugget interface and at the Al SZ.In the continuous development of hybrid structure components, the need for the joining of aluminum alloys to stainless steel (SS) is a great challenge. Much research has been conducted to study the possibility and feasibility of FSW as a green process to weld aluminum alloys to stainless steel ,49,50,51The stainless steels AISI 304 and AISI 316 are popular stainless steels used in different industrial sectors due to their good mechanical properties and corrosion resistance in addition to their lower cost. Joining AISI 304 and AISI 316 stainless steels to aluminum alloys remains a great challenge. Some previous studies concerning this combination focused on the microstructure evolution in different joining configurations. In butt joining configuration, some investigations dealt with the relation between mechanical strength and the existence of stainless steel particles in the aluminum or on the IMC growth following the main process parameters ,61,62,63Jabraeili et al.  studied The improved UTS may be due to the enhanced material plastic flow and partial annealing effect in dissimilar materials due to the preheating of the SS surface by GTAW, resulting in the significantly increased elongation of welds. On the other hand, with the softening of the SZ, the hardness decreased about 50% in regard to the aluminum alloy BM. Paventhan et al.  welded ADue to a lack of literature studying the FSW of AA6061 and AISI 316 SS, and since both materials are crucial combinations in many industries such as the automotive industry, the main objective of this work was to investigate the FSW dissimilar butt joining of 3 mm thickness Al 6061-T6/AISI 316 SS. In addition, extensive microstructure investigations of the SZ and the nugget interface were performed with EBSD to reveal the recrystallization and deformation in both welded materials. Mechanical properties were investigated through uniaxial tensile tests and indentation hardness tests.5 mm3 s−1 to avoid the surface oxidation of the friction-stir-welded zone. Load control mode was employed in the current experiments to keep the forging load of the tool constant for every experiment at 15 kN. The rotational speeds were within the range of 300 to 600 RPM and the travel speeds were 20 and 30 cm/min−1.The AISI 316SS and 6061-T6 aluminum alloy sheets with dimensions of 120 mm × 50 mm × 3 mm were selected as base metals (BMs). The chemical composition and mechanical properties of the BMs are summarized in −3 s−1. To achieve accurate measuring of the tensile properties, an external extensometer was used. Micro-indentation experiments were carried out using a calibrated micro-indenter CSM equipped with a standard Berkovich indenter. The micro-indentation hardness (HIT) tests were conducted by increasing the load up to a maximum force of 2 N at loading and unloading rates of 66.66 mN/s with a holding time of 15 s. The average of 5 HIT measurements for each zone was used. Based on the loading–unloading cycles, the force–penetration depth (F-D) curves were obtained up to the maximum indentation force of 2 N.For the metallographic examination using EBSD, the dissimilar SS/Al butt joints welded by FSW were sectioned perpendicular to the welding direction, and the transverse cross-section was metallographically prepared according to the standard preparation technique, i.e., mechanically ground using SiC papers, then ground down to 1 µm by using a diamond suspension, and finally chemically polished using a 0.05 µm colloidal suspension of silica for about 10 min. The microstructural characteristics of the fusion zone (FZ) and thermomechanical affected zone (TMAZ) were studied using a field-emission gun scanning electron microscope (FEG-SEM)  that was equipped with electron backscatter diffraction (EBSD) capability with step sizes 0.4, 0.2, and 0.1 μm for 250X, 500X, and 1000X, respectively. The weld morphologies at different FSW rotation speeds, such as mixed zone size and geometry, were investigated using a laser scanning confocal microscope . In accordance with the ASTM E8/8M standard, subsize tensile specimens with a gauge length of 32 mm and width of 6 mm were then machined perpendicular to the welding direction as shown in Typical microstructures of the base metals (BMs) used in processing the dissimilar friction-stir-welded butt joints are shown in The appearances and a corresponding cross-sectional view of the friction-stir-welded (FSWed) 6061-T6/AISI 316 SS butt joints at 300–600 RPM are provided in Optical micrographs of the cross-sections that are perpendicular to the welding path of the joints at different tool RPMs are shown in 3, in addition to 14% for FeAl6 at 500 RPM. This result was in agreement with Li et al. [3Al and FeAl3 IMCs along the weld interface.An X-ray diffraction analysis was used to determine the aluminum/steel IMCs generated by the FSW process. Aluminum, aluminum nickel, iron, aluminum chrome, and aluminum iron intermetallic peaks were detected as shown in i et al. , who obtTo analyze the effect of welding rotation speed on the microstructural features, and to disclose more details of the microstructure formation mechanism of the SZ, electron backscatter diffraction (EBSD) was employed at low and high magnifications. The recrystallization and deformation analyses of both sides at 300 RPM are shown in A general view of the microstructure of the SZ interface at 400 RPM is shown in The recrystallization and deformation analyses of both sides at 400 RPM are shown in A general view of the microstructure of the SZ interface at 500 RPM is shown in The recrystallization and deformation analyses of both sides at 500 RPM are shown in After cutting two tensile samples from each FSWed sheet, tensile tests were performed and compared for their UTS values. The as-received 6061-T6 plate showed a UTS of 290 MPa. The highest UTS in the FSWed samples had a UTS equal to 56% of that of the as-received Al sheet at 500 RPM and 20 cm/min traverse speed. The lower UTS of the welded samples compared to the parent metal is 44% at 300 RPM and 30 cm/min traverse speed. The low UTS for welded specimens could be attributed to the formation of intermetallic compounds in the weld interface. IT of the Al 6061-T6 and AISI316 SS BMs are 0.65 and 2.98 GPa, respectively. The average HIT of the welded joint AISI316 SS SZ and the Al SZ at 300 RPM were 0.578 and 5.038 GPa, respectively. The average HIT of the welded joint AISI316 SS SZ and the Al SZ at 400 RPM were 0.586 and 3.385 GPa, respectively. The average HIT of the welded joint AISI316 SS SZ and the Al SZ at 500 RPM were 0.63 and 3.6 GPa, respectively. It is obvious that the hardness of the SZ of the Al side increases with an increase in the RPM; this is due to the grain refinement of the stirred zone in addition to the increase in the amount of SS fragments in the Al nugget which reinforces the matrix. Normally, the hardness of the Al nugget decreases compared with that of the Al BM; this is of course due to the loss of strengthening heat treatment applied to the BM before FSW, despite the effect of the grain refinement after FSW [IT for the TMAZ of the Al side was nearly equal to the HIT of the Al BM, while the HIT of the TMAZ of the SS side was nearly equal to the SS SZ.The typical micro-indentation load–penetration depth (P–h) curves of the BMs and the different zones of the FSWed dissimilar joints at different RPMs are summarized in fter FSW . On the fter FSW ,73. The Successful butt joints were obtained between stainless steel AISI316 and the aluminum alloy AA6061-T6.6, FeAl3, Ni3Al, Al11Cr2, and FeCr.At the interface of the Al and SS, many kinds of IMCs were found, including FeAlDissimilar welded butt joints show very fine recrystallized grains for Al 606 and very fine deformed grains of the AISI 316 SZ with HAGBs and LAGBs, respectively.The highest obtained UTS of 160 MPa was found for the joint at 500 RPM and 20 cm/min traverse speed, which is 56% of that of the Al BM. In addition, all tensile specimens were fractured at the aluminum SZ.In this study, the effect of FSW rotation speed on the microstructure and the mechanical properties of the dissimilar stainless steel AISI316 and aluminum alloy AA6061-T6 butt joints were investigated. The main results of this research can be summarized as follows:The SZ hardness of the Al side increased from 0.578 to 0.63 GPa with an increase in the rotation speed from 300 to 500 RPM, due to the SZ grain refinement and the increase in SS fragments in the Al nugget. On the other hand, the SZ hardness of the SS side decreased from 5.038 to 3.6 GPa with an increase in the RPM.


The inclusions in the experimental steel welding HAZ with Mg elements were mainly elliptical composite inclusions composed of (Mg-Zr-O) + MnS. Moreover, MnS precipitated on the surface of the Mg-containing inclusions in the welding HAZ. Intragranular acicular ferrite (IAF) nucleation was primarily induced via the minimum lattice mismatch mechanism, supplemented with stress-strain energy and inert interface energy mechanisms.With the development of the pressure vessel industry, high-energy wire welding has a great future. However, this means higher demands on the weldability of pressure vessel steels. Controlling inclusions via oxidative metallurgy is a reliable method of improving the weldability of pressure vessel steels. Hence, in this paper, experimental steels with different Mg element mass fractions were prepared using vacuum metallurgy. Simulated welding for high-heat input welding was carried out using the Gleeble-2000 welding thermal simulation test machine. The inclusions in the welding heat-affected zone (HAZ) in the experimental steels were observed using an optical microscope (OM) and scanning electron microscope (SEM). The compositions of the inclusions were analyzed using an energy-dispersive spectrometer (EDS). The research results indicated that the addition of Mg could increase the number density of the inclusions in the welding HAZ. With the addition of Mg from 0 to 5 wt.%, the total number density of the inclusions increased from 133 to 687 pieces/mm Pressure vessel steel is used to manufacture pressure vessels or other similar equipment, such as petroleum, gas storage, and transportation ,2. As prTo improve the weldability of pressure vessel steels and achieve the objective of increasing the toughness of the welding HAZ, the addition of particles to form dispersed and fine inclusions has been successful. As summarized in the literature ,11,12, t2O3 to Ti2O3 and finally to TiC. Acicular ferrite was induced to nucleate by Ti2O3 to form Mn-depleted zones, whereas Al2O3 and TiC could not nucleate via this mechanism. Yao et al. [To obtain the right type of inclusions to induce IAF, many researchers have controlled the formation of inclusions by adding deoxidizing elements, such as Ti, Zr, and Mg, to steel ,14,15. Fo et al.  investigo et al. . The reso et al.  researchThe formation of a microstructure in the welding HAZ of pressure vessel steels is affected by the type and size of the inclusions that serve as the core of IAF nucleation ,21,22. WIn this paper, the effects of Mg elements on the inclusion characteristics  of the welding HAZs for pressure vessel steels were studied. The mechanisms of IAF nucleation induced by the inclusions containing Mg in the welding HAZ of pressure vessel steels were investigated, and a reference is provided for the design of the composition of pressure vessel steels for high-heat input welding.This experiment used the BJ-VIM-5 vacuum induction melting furnace  to smelt the experimental steel. The device is shown in In this experiment, the alkaline earth element Mg was added as the deoxidizer. According to the different mass fractions of Mg elements in the experimental steels, three groups of experimental steels were designed to be smelted, and each group smelted 5 kg. The designed addition amount (wt.%) of Mg for each group of experimental steels is shown in The controlled rolling and cooling equipment  are shown in In order to obtain a sample of the designated area of the welding HAZ of sufficient size and to analyze it, the method of welding heat simulation is usually used ,24. It c8/5 was set to 80 s. The fifth step was to gradually cool down from 500 °C to room temperature. As shown in The inclusions in the welding HAZ were visualized using an OLYMPUS-CK40M optical microscope , as shown in The inclusions in the experimental steel welding HAZ were studied in terms of the number and size of the inclusions. Combining the results of related studies ,27, the 2. The total number density of the inclusions in the welding HAZ of experimental steels M1, M3, and M5 with magnesium as the deoxidizer is higher than that in R, which is 291 pieces/mm2, 408 pieces/mm2, and 657 pieces/mm2, respectively. This shows that the addition of Mg elements promotes the formation of fine inclusions in the experimental steel welding HAZ to a certain extent under the present experimental conditions. Combining the results of related studies [2, it is the most suitable size of inclusions to play the role of pinning grain boundaries and inducing IAF nucleation. These are called the effective inclusions.The sum of the number density of the inclusions of each size is called the total number density of inclusions. As seen in  studies ,29, it c2 for R. In addition, as the Mg content increases, the density number of the effective inclusions in the welding HAZ of the experimental steel increases: 255 pieces/mm2 for M1 and 316 pieces/mm2 for M2. When the mass fraction of 5wt.% Mg is added in the welding HAZ of the experimental steel, and the number density of the effective inclusions is also the largest, with 579 pieces/mm2. The changing trend of the number density of the total inclusions and the number density of effective inclusions of each experimental steel is shown in 2, these nanoscale size inclusions could play the role of pinning grain boundaries and inhibit grain growth and coarsening in the welding HAZ. When the area of the inclusion is 0.5–5 μm2, these micro-grade inclusions are at the most suitable size for inducing IAF nucleation. The more IAF microstructures in the welding HAZ, the better the strength and toughness. When the area of the inclusion is greater than 5 μm2, these larger-sized inclusions are not very effective in pinning grain boundaries and inducing IAF nucleation [Only the number density of the total inclusions and effective inclusions is discussed above. To reflect more specifically the effect of inclusions on the strength and toughness of the welding HAZ in each experiment, the inclusions are categorized according to their different roles in different size ranges. When the area of the inclusion is less than 0.5 μmcleation . Therefo2 for areas less than 0.5 μm2 and 54 pieces/mm2 for areas in the 0.5–5 μm2 range. Therefore, the number density of inclusions that both pin and induce IAF nucleation is relatively minimal, which leads to the poor strength and toughness of the R steel. In contrast, in the three experimental steels with Mg elements, the number of inclusions that perform the role of pinning and inducing IAF nucleation increases gradually, and both are significantly higher than the R steel, except that the number of pinning inclusions in the welding HAZ of the experimental steel with 3 wt.% Mg is higher than that of the inclusions which induce IAF nucleation. The inclusions in the remaining two groups of experimental steels with Mg elements are mainly used for inducing IAF nucleation. Among them, the 116 pieces/mm2, 171 pieces/mm2, and 242 pieces/mm2 inclusions with an area less than 0.5 μm2 were found in the M1, M3, and M5 steels, respectively. The number density of the inclusions in the 0.5–5 μm2 interval was 139 pieces/mm2, 145 pieces/mm2, and 337 pieces/mm2 for M1, M3, and M5, respectively. It was observed that the addition of Mg elements facilitates the production of more inclusions that induce IAF nucleation in the experimental steel welding HAZ.As shown in In this experiment, an S-4800 SEM and a supporting EDS were used to research the R steel following emery paper grinding and mechanical polishing, as well as the specimen of the welding HAZ in the experimental steel containing Mg. The main inclusions were found for the shape observation and composition analysis. The results are shown in 2O3) is prone to accumulate in steel fluid to form coarse inclusions. This inclusion has no induction effect on IAF, and it is easy to form cracks during processing, which damages the toughness of the welding HAZ of the material to a certain extent and is an undesirable inclusion. As shown in As shown in The alkaline earth metal Mg causes the shape of the inclusion to be mostly spherical, with a very small size of approximately 1.5 μm, which is in the most suitable size range of inclusions for IAF nucleation as described above. Moreover, there are more inclusions of this size in the experimental steel welding HAZ, and the amount of IAF induced, therefore, is also large, which is conducive to the improvement of the strength and toughness of the experimental steel welding HAZ.The morphology and line scanning analysis of typical inclusions in the welding HAZ of experimental steels with Mg are shown in By observing the morphology and line scanning results of the typical inclusions in the welding HAZ of the experimental steel with Mg added, the following results were found: firstly, from the morphology of the inclusions, spherical or nearly spherical inclusions are produced. The reason is that the spheroidization of Mg elements as alkaline earth metals changes the morphology of the inclusions in the welding HAZ of all experimental steels. Secondly, from the line scanning distribution of the elements in the inclusions, Mg elements are generally combined with other elements to form (Mg-Zr-O) + MnS composite inclusions. After corroding the welding HAZ metallographic specimen of the experimental steels with Mg added to them, the typical IAF microstructure formed by the fine circular inclusions was found, as shown in The addition of Mg could promote the spheroidization of the inclusions. The (Mg-Zr-O) composite inclusions containing Mg could effectively induce IAF nucleation and improve the strength and toughness of the welding HAZ in experimental steels. It can be clearly seen from the position of the inclusion that two more ‘bulky’ primary IAF microstructures are formed. Secondary IAF microstructures are formed via the inductive nucleation mode of primary IAF microstructures. The relatively ‘thick’ primary IAF microstructure is the main trunk, and, at the same time, many branch IAF microstructures continue to be induced on the trunk. This is the refinement effect of the IAF microstructure itself. Many IAF microstructures are intertwined and firmly combined with each other, playing a role in improving the strength and toughness of the HAZ in experimental steel welding. The inclusions that promote IAF nucleation are affected by the interface energy of themselves or between the precipitates and the ferrite, and the interface energy between them is determined via lattice mismatch. It is shown that ,32 the iAs shown in −6 K−1, while that of the MgO is 13.8 × 10−6 K−1, which is only close to half of that of austenite. Thus, a large stress-strain field is generated around the inclusion to power IAF nucleation. However, it is also taken into account that the energy required for ferrite nucleation is often one to two orders of magnitude larger than the activation energy generated by thermal expansion differences alone. Therefore, stress-strain energy only exists as an auxiliary mechanism to induce IAF nucleation in the welding HAZ of experimental steels with Mg elements.Due to the high density of dislocations in the IAF microstructure, the average coefficient of the thermal expansion of the inclusions during high-heat input welding is small, whereas the coefficient of thermal expansion of the austenitic matrix is relatively large. Thus, a stress-strain field is formed around the inclusion, causing a certain degree of distortion. The resulting distortion could provide activation energy to induce IAF nucleation. Data ,37 showsMn elements are poor around inclusions. The Mn content is significantly reduced within a certain range, and a poor Mn area is formed. This would produce local composition changes and induce IAF nucleation ,39. TherAs shown in 5 to 106 J/mol. This value is close to the lowest energy required for inducing IAF nucleation (approximately 106 J/mol). However, simply relying on an inert interface energy mechanism is not enough to fully explain the nucleation mechanism of IAF microstructures.Ricks et al.  suggeste(1)2 and 122 pieces/mm2, respectively. In contrast, the welding HAZ of the experimental steel with 5 wt.% Mg added exhibits the highest total number density of inclusions and the number density of effective inclusions, amounting to 656.39 pieces/mm2 and 579.10 pieces/mm2, respectively. With increasing Mg content, the number density of the total inclusions and the number density of the effective inclusions in the experimental steel welding HAZ show an upward trend. The total number density of the inclusions and the number of effective density inclusions in the welding HAZ of the experimental steel without added Mg are the lowest, with 132 pieces/mm(2)In the three experimental steels with Mg elements, the number density of the inclusions that play the role of pinning and inducing IAF nucleation increases gradually and is markedly higher than that of the R steel. The addition of Mg elements is beneficial to produce more inclusions inducing IAF nucleation in the welding HAZ of the experimental steel under the experimental conditions.(3)The inclusions in the experimental steel welding HAZ with Mg elements are mainly elliptical composite inclusions composed of (Mg-Zr-O) + MnS with a very small size of approximately 1.5 μm. The inclusions with such shape and size are conducive to the nucleation and growth of ductile IAF microstructures. (4)After the addition of Mg elements, MnS is precipitated on the surface of Mg-containing inclusions in the welding HAZ. IAF nucleation is induced mainly via a minimum lattice mismatch mechanism, supplemented by stress-strain energy and inert interface energy mechanisms.


The tribological properties of the modified PTFE composites were tested using a linear reciprocating friction and wear tester, and the entire friction experiment was designed in seven separate stages. Morphological features were extracted and analyzed from photographs of the transfer film acquired by optical microscopy at each friction stage using an image processing program. The thickness and roughness of the transfer film sections were measured using a non-contact profilometer. Abrasive debris were collected, and their morphological features were observed with an electron microscope. The results showed that the synergistic addition of soft PEEK and hard Nano-ZrO2 particles effectively inhibited interlayer slippage between PTFE molecular chains, dramatically reducing the size and yield of abrasive debris, and facilitated the improvement of the thickness and firmness of the transfer film, which significantly enhanced the wear resistance of the PTFE composites (the lowest volumetric wear rate for Nano-ZrO2/PEEK/PTFE was only 1.76 × 10−4 mm3/Nm). Quantitative analyses of the morphological characteristics of the transfer films revealed that the coverage and roundness of the transfer films gradually increase with the friction stroke, while the aspect ratio and texture entropy subsequently decrease gradually. The coverage, area, mean, third-order moments, and consistency of the transfer film strongly correlated with the volumetric wear rate (correlation coefficient |r| > 0.9).The materials tribology community has identified that the transfer film attached to the surface of the counterpart metal during the friction process is not only closely related to the filler modification material but also a key factor affecting the tribological properties of polymer composites; however, there is a lack of feasible methods to quantify the characteristics of the transfer film. In this study, Nano-ZrO The results showed that glass fibers as a single filler deteriorate the wear resistance of PTFE composites dramatically. However, the combination of MoS2 and glass fibers can synergistically enhance the tribological properties of PTFE. Amenta et al. [2O3 nanoparticles had four orders of magnitude lower volumetric wear rates than unfilled PTFE. Sun et al. [PTFE is widely used as a solid lubricating material in space machinery, marine engineering equipment, and medical devices ,2,3. Thia et al.  investiga et al.  found tha et al.  found thn et al.  systematn et al.  investig−7 mm3/Nm) in PTFE composites, that a well-modified filler reduces the size of the abrasive chips contributing to the formation of a stable transfer nucleus, that a stable transfer film reduces the transfer wear rate, and that the stability of the friction interface provides the time required for the friction chemistry to react. The morphological characteristics of transfer films are an essential aspect of interest to researchers and are usually observed, characterized, and analyzed using optical or electron microscopy [−1, and based on this relationship, the thickness of the transfer film was measured using infrared transmission techniques. Currently, there needs to be a set of quantitative methods to characterize the morphology of the transfer film, as well as a study of the correlation between the quantified transfer film characteristics and the tribological properties of the material.Polymers as lubricant materials are usually paired with metallic materials to form sliding friction pairs. Due to the high surface energy and hardness of the metal material, the microscopic concave and convex summit on the surface of the counterpart metal produce a scraping effect on the polymer surface during the friction process, resulting in a portion of the material on the polymer body transferring to the counterpart metal surface, aggregating and adhering to it, thus forming a thin film-like medium, also known as a “transfer film” ,25,26,27croscopy ,35,36,37croscopy  measuredcroscopy  found a 2 nanoparticles and soft PEEK particles. The focus was on the effect of the two soft and hard fillers on the tribological properties and the evolutionary development of the transfer film morphology during the friction process. Based on the theoretical principles of computer graphics, an image processing program for the automatic identification and quantitative analysis of the morphological characteristics of the transfer film was established employing a computer program. The effect of ZrO2 nanoparticles and PEEK particles on the morphological characteristics of the transfer film at different friction stages was investigated, as well as determining the correlation between the morphological characteristic parameters of the transfer film and the wear resistance of PTFE composites. These morphological characteristics were used as indicators to evaluate the quality of the transfer film, thus helping to understand the effect of the transfer film on tribological properties.The aim of this study was to synergistically enhance the tribological properties of PTFE composites by filling them with hard ZrO2 nanopowder, and PEEK particles. PTFE was purchased from Daikin Industries, Ltd.  under the brand name POLYFLON M-18F, with an average particle size of 25 µm and density of 2.16 g/cm3. ZrO2 nanopowder was purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd.  under the brand name XFI01, with an average particle size of 20–40 nm, density of 5.89 g/cm3, specific surface area of 12.31 m2/g, and purity of 99 wt%. PEEK pellets were purchased from Victrex Ltd.  under the brand name Victrex PEEK 450 PF with an average particle size of 50 µm and density of 1.3 g/cm3.The three raw materials used in this study were PTFE matrix powder, ZrO2 nanoparticles, PEEK particles, and PTFE powder were weighed and formulated using an electronic balance (with an accuracy of 0.1 mg) according to the formulation proportions shown in The preparation process of the PTFE composites is shown in Each PTFE composite was tested in seven separate stages  on a linear reciprocating friction and wear tester , with a cumulative friction test duration of 458.5 min (cumulative friction stroke of 2200.8 m), to observe the evolution of the tribological properties and transfer film characteristics at each stage of friction, as shown in The normal load of 180 N was applied to the top of the specimen , the friction stroke was 20 mm, the motor speed was 120 r/min, and the ambient temperature was 25 °C. After each stage of the friction test, the sample and the counterpart metal were carefully removed from the friction testing machine, and the following observations were made:K of the specimens in each section of the test were calculated.m is the wear weight, ρ is the specimen’s actual density, N is the normal load applied to the sample, and L is the total sliding distance.The specimens were weighed using an electronic balance, then the mass loss and the average volumetric wear rate High-resolution images  of the surface of the paired metal were obtained using an optical microscope  to provide raw image information for subsequent morphological characterization of the transfer film. A non-contact 3D profiler  was used to obtain the thickness and roughness of the transfer film on the counterpart metal surface at each friction stage.After completing the above observations, the specimen and counterpart metal were reinstalled on the friction tester, and the next stage of the friction wear test was carried out. It was important to note that during the dismantling, testing, and mounting process, it was strictly necessary to ensure that the friction surfaces of the specimen and the counter metal were not in direct contact with other substances to avoid contamination and damage to the formed transfer film. At the end of the test, the collected debris was soaked in a dispersant for ultrasonic dispersion. The debris was sprayed with gold before observation by scanning electron microscopy .3 colors). The transfer film RGB image was first converted into a grey-scale image . Then, a 3D distribution of the grey-scale values of the transfer film was generated with the help of a visualization program. These images needed to be pre-processed [The images of the transfer film acquired by optical microscopy were RGB images  and a background area  using the Otsu thresholding method . The greDetermining the target region boundary in the transfer film image is the key to image feature extraction. According to the principles of computer graphics and mathematical set theory, a boundary in an image is a collection of connected pixels on the boundary of two regions with distinctly different characteristics, reflecting jumping changes in the grey-scale of the boundary. Discontinuous features of the grey value on the boundary  can be detected by calculating the derivative. In this paper, the calculus Sobel operator method was used to detect the edge contours of the transfer film. The Sobel operator is able to smooth out the noise and provide more accurate directional information about the edges of the target region in the image so that better results can be obtained for images with gradual grey- scale changes and much noise .(1)Expansion: A morphological operation that blends elements of the background area near the boundary of the target area into the target area.(2)Erosion: A morphological operation that removes the boundary points of the target area from the image.(3)Open operation: Erosion operation followed by expansion operation.(4)Closed operation: The expansion operation is performed first, then the erosion operation is performed.The basic principle of morphological image processing is to use a structural element  to move continuously through the image to check whether the structural element is entirely inside the target area, thereby determining the interrelationship between regions in the image and understanding the structural features of the image. Morphological image processing consists of the following four basic operations:These four basic operations of morphological image processing can remove the convex corners of the target area boundaries, fill in the concave corners and voids in the target area, suppress the noise in the background area, and improve the smoothness of the boundaries, thus facilitating the acquisition of the key shape features in the target area.The morphological features quantified from the transfer film images in this paper included shape features and texture features.The shape feature is a global or local feature used to describe the shape of the transfer film in computer graphics theory. Shape features can be divided into two categories: one is the contour feature that describes the shape of the object’s boundary, and the other is the regional feature that describes the internal shape of the object. Texture features reflect structures with slow or periodic changes in the image. Texture features are represented by sequential repetition of the local structure of the image, random arrangement of structural features, and roughly uniform consistency. Based on the statistical data provided by the grey-scale histogram, the texture information of an image, including interval distance, direction, magnitude of change, and speed of change, was quantified and described by calculating the correlation of the grey-scale values between two points in the image at a certain distance and direction. −4 mm3/Nm. In the subsequent experimental phases, the volume wear rate of pure PTFE remained at a high level of 3 × 10−4 mm3/Nm. The extremely inferior wear resistance of pure PTFE resulted in the frictional wear test being carried out for only the first six stages, with a cumulative friction time of 158.5 min , as shown in The pure PTFE exhibited a very high wear rate during the friction process, especially in the first experimental phase (0~30 s), where the volumetric wear rate was as high as 7.7 × 102 and PEEK showed a gradual decrease throughout the friction process, as shown in −4 mm3/Nm at the initial friction stage to 1 × 10−5 mm3/Nm at the stable friction stage. The lowest value of PEEK/PTFE volumetric wear rate was 3.53 × 10−6 mm3/Nm. The average coefficient of friction of PEEK/PTFE was lower than that of pure PTFE in the early stages and higher than that of pure PTFE in the stable friction stage. Unlike the flakey debris of pure PTFE, PEEK/PTFE produced predominantly ribbon-like debris and had a much smaller width dimension than that of PTFE, as shown in The volumetric wear rates of all three PTFE composites filled with Nano-ZrO2/PTFE decreased significantly during the first four experimental stages, while it leveled off and remained below 1 × 10−5 mm3/Nm during the last three experimental stages. The lowest value of volumetric wear rate for Nano-ZrO2/PTFE was 4.56 × 10−6 mm3/Nm. The average coefficient of friction of Nano-ZrO2/PTFE varied relatively little over the seven friction stages, remaining at around 0.24. In the stable friction stages, the volume wear rate of Nano-ZrO2/PEEK/PTFE was only 1.76 × 10−6 mm3/Nm, showing the best wear resistance of the four specimens. The average coefficient of friction of Nano-ZrO2/PEEK/PTFE at the later stages of the experiment was 0.22, lower than the 0.24 of Nano-ZrO2/PTFE for the same period. Both Nano-ZrO2/PTFE and Nano-ZrO2/PEEK/PTFE friction produced debris with a powdery morphological character, and the size of Nano-ZrO2/PEEK/PTFE debris was smaller, as shown in 2/PTFE and Nano-ZrO2/PEEK/PTFE on the surface of the counterpart metal exceeded 500 nm, significantly higher than the transfer film thickness of pure PTFE and PEEK/PTFE, as shown in 2 particles dispersed in the PTFE matrix acted as a backbone to support and enhance the creep resistance, compressive strength, and hardness of the PTFE composites, thus effectively inhibiting the interlayer slip between the carbon–carbon molecular chains of PTFE. The soft PEEK particles in Nano-ZrO2/PEEK/PTFE act as a link between the hard Nano-ZrO2 particles and the PTFE matrix, thus exhibiting both optimum wear resistance and better lubricity than Nano-ZrO2/PTFE.The volume wear rate of Nano-ZrO2/PTFE and Nano-ZrO2/PEEK/PTFE covered most of the friction area and showed noticeable scuff marks. In contrast, the transfer films formed by PEEK/PTFE during the same period had a smaller area, indicating that the nanoparticles were beneficial in increasing the formation rate of the transfer film. In the later stages of the friction experiments, the transfer films formed by all three materials covered the entire friction area, showing good coverage.At 30 min, the transfer films formed by Nano-ZrO2. In contrast, the surface of the PEEK/PTFE counterpart was relatively clean, with minimal transfer film covering it during the same period. At the same time, Nano-ZrO2/PEEK/PTFE had the best transfer film coverage among the three. By the end of the rubbing period, the transfer film thickness and distribution uniformity of Nano-ZrO2/PEEK/PTFE were significantly better than those of the other two materials.2/PEEK/PTFE was 0.55 when the friction test was carried out for up to 5 min. The transfer film coverage of Nano-ZrO2/PTFE and PEEK/PTFE during the same period was 0.51 and 0.45, respectively, indicating that the hard nanoparticles contribute to the rapid formation of a transfer film on the surface of the counterpart metal at the beginning of the friction. The transfer film coverage of Nano-ZrO2/PTFE was lower than that of the other two PTFE composites filled with PEEK particles at the same period when the friction test lasted up to 30 min, due to the relatively soft PEEK particles facilitating enhanced transfer film firmness, thus maintaining the integrity of the composite on the surface of the counterpart metal. Nano-ZrO2/PEEK/PTFE exhibited the best transfer film coverage at different stages of the friction experiments, and it also had the lowest wear rate of the three PTFE composites over the same period, suggesting that the hard nanoparticles and the soft PEEK filler can synergistically improve the transfer film coverage as well as the wear resistance.The coverage area of the transfer film and coverage ratio are quantitative indicators to measure the integrity of the transfer film on the surface of the counterpart metal. All three groups of PTFE-reinforced materials showed a gradual increase in transfer film area coverage with the growth of the friction stroke, and the growth rate was faster in the early stages of friction and gradually stabilized in the later stages, as shown in 2/PTFE and Nano-ZrO2/PEEK/PTFE showed a trend of increasing first and then decreasing. This trend in the transfer film also corroborated the change in wear rate, indicating that the hard nanoparticles scrape the already-formed transfer film in the later stages of friction and split the larger transfer film into smaller ones.Comparing two counterpart metal surfaces with the same value for the coverage of transfer film, if the average area of individual transfer films covering one of the surfaces is smaller, the greater the number of individual transfer films. The aspect ratios of the transfer films of all three PTFE composites gradually decreased as the frictional stroke increased, indicating that the transfer films were gradually fusing and expanding, as shown in The degree of circularity can measure the similarity of the transfer film boundary profile to a circle. The greater the roundness value, the greater the similarity of the transfer film contour to a circle. As shown in 2/PEEK/PTFE transfer film was higher than that of the other two transfer films at all friction stages. However, the rectangularity of the three materials did not show a significant trend throughout the friction process, as shown in The similarity between the boundary profile of the transfer film and its outer rectangle can be measured by the degree of rectangularity. The rectangularity of the Nano-ZrO2/PTFE, and both were higher than that of Nano-ZrO2/PEEK/PTFE. For the rest of the friction period, the mean value of Nano-ZrO2/PEEK/PTFE was the lowest among the three transfer films, followed by Nano-ZrO2/PTFE, and the mean value of PEEK/PTFE was higher than the former two.The mean value is a quantitative measure of the average luminance of the pixels in a transfer film image. As the reflectivity of the metal material is stronger than that of the transfer film, a lower mean value indicates a smaller area of exposed counterpart metal. At the initial stage of friction, the mean values of all three transfer films showed a significant decreasing trend, then the changing trend became stable, as shown in The third-order moment measures the degree of skewness of the color components (color asymmetry) in the transfer film image. As shown in Uniformity is a quantitative measure of the smoothness of the transfer film texture, with higher values indicating a smoother texture and lower values indicating a rougher texture. The uniformity of the PEEK/PTFE transfer film showed a trend of continuous growth with the increase of the friction stroke, indicating that the texture of the transfer film was rough at the beginning of the friction, then gradually evolved towards a smooth texture, as shown in The texture entropy reflects the change in greyscale in the transfer film image, with higher texture entropy indicating a greater complexity of grey-scale changes in the image and vice versa. The texture entropy of all three material transfer films showed a gradual decrease with increasing friction stroke, which indicates that the complexity of the grey-scale of the transfer film was also gradually decreasing, as shown in x” represents the morphological characteristics of the transfer film, “y” represents the tribological properties of the PTFE composites at different friction stages, and “r” denotes the correlation coefficient between “x” and “y”. The analysis focused on examining the correlation between the morphological characteristics of the transfer film formed at various friction stages and the volumetric wear rate, using the calculation formula of Pearson’s correlation principle expressed as follows:r|) greater than 0.95 is considered significant, while a value equal to or greater than 0.8 indicates a high correlation. On the other hand, a correlation coefficient falling within the range of 0.5 to less than 0.8 is classified as moderate, while values between 0.3 and 0.5 indicate a low correlation. Lastly, a correlation coefficient below 0.3 signifies no correlation between the variables under examination.In correlation analysis, a correlation coefficient −4 mm3/Nm). Adding PEEK particles and ZrO2 nanoparticles to the PTFE matrix effectively suppressed interlayer slip and improved the shear deformation resistance of the matrix. The hard ZrO2 nanoparticles were highly efficient at cutting through debris detached from the matrix, resulting in a noticeable reduction in the size  and the number of abrasive chips and, therefore, a significant improvement in the wear resistance of the PTFE composite (10−6 mm3/Nm). In particular, the volumetric wear rate of Nano-ZrO2/PEEK/PTFE was only 1.76 × 10−6 mm3/Nm at the late friction stage.Pure PTFE generated many flakes of considerable size  during friction due to the slip motion between the carbon–carbon molecular chains, resulting in low wear resistance (3 × 10(2)2/PTFE.The PEEK and nanoparticles facilitated the formation of a firm and stable transfer film on the surface of the counterpart metal, and the nanoparticles, in particular, greatly increased the thickness of the transfer film during the stable friction phase, which also resulted in a higher coefficient of friction compared to pure PTFE. The soft PEEK particles dispersed in the matrix could effectively encapsulate the hard nanoparticles, which acted as a link between the PTFE matrix and the nanoparticles, so the increase in friction coefficient was not as large as that of Nano-ZrO(3)The morphological characteristics of the transfer film evolved dynamically during the friction process, in which the transfer film’s coverage, roundness, third-order moment, and consistency showed an increasing trend. In contrast, the aspect ratio and texture entropy demonstrated a gradual decrease. The trend of these morphological characteristics indicated that the transfer film gradually fused during the friction process, and the haphazardness of the transfer film shape gradually decreased. The correlation analysis showed that the five morphological characteristics of transfer film coverage, area, mean value, third-order moment, and consistency exhibited a significant correlation with the volume wear rate of the PTFE composite.


Characterisations of the ball-milled composite powders were performed by scanning electron microscopy (SEM), X-ray diffraction, and measurement of the particle size distribution. The effect of the sintering temperature  and pressure (20 MPa and 35 MPa) on the density, porosity, and Young’s modulus was investigated. The relationship between the change of Orb content and physical, mechanical, and electrical properties was studied. Experimental data showed that the properties of Cu–Orb composites depended significantly on the SPS sintering conditions. The optimal sintering temperature was 1223 K with a pressure of 35 MPa. Composites exhibited a high degree of consolidation. For these materials, the apparent density was in the range of 93–97%. The results showed that the higher content of Orb in the copper matrix was responsible for the improvement in Young’s modulus and hardness with the reduction of the conductivity of sintered composites. The results showed that Young’s modulus and the hardness of the Cu 20% Orb composites were the highest, and were 165 GPa and 174 HV0.3, respectively. These composites had the lowest relative electrical conductivity of 17%.Copper matrix composites with zirconium diboride (ZrB Copper and its alloys are widely used because of their excellent electrical, thermal, and mechanical properties, among others, in the aviation, railway, military, and electronics industries . At the 2 composites. They showed that as the Orb content increased, the hardness and abrasion resistance of the composites increased. At the same time, the electrical conductivity of the composites decreased. In turn, Wang et al. [2 content (1–9 wt%).Pure copper (Cu) is characterised by high electrical and thermal conductivity and good corrosion resistance, but unfortunately low strength and wear resistance . Orb is g et al.  produced2 content increased to 7 wt% and then decreased. In another work [2  on the mechanical properties and abrasive wear of copper. An improvement in wear resistance, hardness, and compressive strength was observed with an increase in the amount of reinforcement phase in the copper matrix.However, the microhardness reached a maximum value of 100.8 HV0.2 when the ZrBher work , Shaik aSpark plasma sintering (SPS) is widely used to consolidate various materials such as metals ,36, cerm2. The first stage of the research focused on the characteristics of composite powder mixtures with various ZrB2 contents prepared by milling in a high-energy ball mill. Then the influence of the sintering conditions (temperature and pressure) and the content of the ZrB2 reinforcing phase  on the physical, mechanical, and electrical properties of the composites were examined.In the present study, SPS technology was used for the consolidation of the Cu composites reinforced with ZrBThe composite materials were made of copper powders  which comprised the matrix material and zirconium diboride powder  constituting the reinforcement of the composite. 2, Cu + 10 wt% ZrB2, Cu + 15 wt% ZrB2, and Cu 20 wt% ZrB2. The powders were milled using the following cycle: 20 min of milling—10 min break. The balls/powder weight ratio was 1:5 (50 g: 250 g). The container and balls used were made of tungsten carbide. The mechanical milling of the composite mixtures was performed in high-energy planetary ball mill Pulverisette 4 . Four composite mixtures were prepared with the following composition: Cu + 5 wt% ZrBThe powders were sintered by SPS . The sintering process was carried out in an argon atmosphere under a pressure of 20 MPa and 35 Mpa for 5 min. To explore the effect of sintering temperature on the properties of the composites, the sintering temperature was set at 1123 K, 1173 K, and 1223 K. The furnace heating rate was kept at 473 K/min. The samples were cooled at a rate of 373 K/min. The powder mixtures were put into a cylindrical graphite die with an inner diameter of 20 mm. After the sintering process, the samples had a height of 7–8 mm. During the SPS process, the temperature was monitored with a pyrometer. The density of the sintered composites was measured by Archimedes’ principle. Relative density is the ratio of measured density to theoretical density. An analytical balance RADWAG AS 220/C/2  was used to measure the weight of the samples. Young’s modulus was determined using the Panametrics Epoch III flaw detector . Young’s modulus was measured based on the velocity of ultrasonic waves transition through the sinter. The velocities of the transverse and longitudinal waves were calculated as the ratio of sample thickness to relevant transition time. For each sample, five measurements of Young’s modulus were performed. The measurement error was 2%.The NEXUS 4000 microhardness tester  was used to measure the average hardness of the composites at the load of 2.942 N and a hold time of 10 s. Each sample was tested with 10 points.X-ray diffraction analysis (XRD) was carried out using a diffractometer equipped with a Cu/Kα radiation. The microstructures of the sintered composites were evaluated using scanning electron microscopy  equipped with energy-dispersive spectroscopy .The electrical conductivity of the samples was determined according to the diagram in 2 milled for 5, 10, 15, and 20 h, respectively, are shown in 2 powder particles were shaped like polyhedra with sharp edges . They also revealed the presence of small amounts of CuZr and Zr phases in the powder mixtures. Similar test results were obtained for all composite powders. No changes in the intensity of the peaks originating from Cu, ZrB2, Zr, and CuZr were observed in the diffractograms as the milling time increased.Furthermore, the results of testing the composite mixtures  showed tectively . During ncreases . Figure 2 composites were evaluated in terms of the degree of compaction (density and porosity) to indicate optimal sintering conditions. An additional parameter taken into account in the optimisation of the sintering conditions was the value of Young’s modulus determined using the ultrasonic method. The results of the tests on the influence of the sintering pressure and temperature on the properties analysed are presented in 2 composites, the temperatures of 1123 K and 1173 K are insufficient to obtain a high degree of densification. The negative effect of these sintering conditions was particularly clearly observed for The parameters of the SPS process play a significant role in shaping the properties of the sintered materials. Therefore, in the first stage of the research, optimisation of the sintering conditions was carried out. Sintered Cu–ZrB6-TiB2) composites also prepared using the SPS method. Meanwhile, increasing the temperature of the SPS process to 1223 K improved the density of the composites and porosity, and increased Young’s modulus. For this sintering temperature, the highest values of relative density above 90%, low porosity, and a higher Young’s modulus in the range (92–96%) were achieved. Increasing the sintering temperature is beneficial because a higher temperature accelerates atomic diffusion and increases the migration rate of grain boundaries, which in turn promotes a reduction of pore size and an improvement in density ,57. This2-reinforcing phase (3 to 7.57 g/cm3 with an increase in the content of ZrB2 (5–20%). The reduction in the density of the composites is mainly due to the lower density of ZrB2 ceramics (6.10 g/cm3) compared to copper (8.96 g/cm3) [2 composites using a hot-pressing sintering process at a temperature of 840 °C and a pressure of 25 MPa. A decrease in density was found (from 96.1 to 91.3%) when the ZrB2 content was changed (1–9 wt%). The test results showed that the Young’s modulus increased with the increase in the ZrB2 content in the copper matrix  compared to sintered copper (61 HV0.3). This is the result of the presence of the ZrB2 reinforcement phase in the copper matrix, which has a very high hardness  ,60,61. W6 g/cm3)  observedr matrix . The val content . Further>2200 HV ). The img et.al.  reported2 composites. For comparison, 2 and Cu–20 wt% ZrB2 composites. A uniform distribution of the reinforcing phase was observed in the copper matrix. Only for composites containing 20 wt% ZrB2, the local formation of ZrB2 agglomerates was demonstrated  and phase composition (X-ray diffraction) analyses were carried out for all sintered Cu–ZrBnstrated . Phase anstrated  confirme2 caused a strong decrease in the electrical conductivity of the composites. The effect was most visible with 10% of the content of the reinforcement phase and more. This was caused by a sharp reduction in the share of pure copper in the active cross section of the material. The observed decrease amount and its subsequent stabilisation at a constant level may indicate partial diffusion of the components from zirconium diboride into the copper matrix. According to [Comparisons of relative electrical conductivity for sintered materials are presented in rding to , the solrding to . Such a 2 in the composite powders improves the uniformity of particle distribution. Moreover, the particle size distribution curve undergoes favourable changes, which tends toward an ideal Gaussian curve without a clear maximum. This effect is especially visible for the content of 5 and 10 wt% ZrB2 , the formation of conglomerates of ZrB2 particles can be observed. This is an unfavourable phenomenon and may indicate microstructure homogeneity problems for ZrB2 contents of 20 wt% and above. The phase analysis of the sintered composites  diffusion exchange of components, it should be proportional to the volume fraction of the reinforcing phase. However, for solution hardening materials, where alloy addition occurs evenly throughout the matrix and modifies the parameters of the crystal lattice by introducing more point defects and, consequently, conduction electron scattering centres, even a small amount of the addition may cause a significant decrease in the electrical conductivity of the material.j) in a conductor:σ—electrical conductivity tensor, E—vector of electric field intensity, andA similar relationship occurs for thermal conductivity, which has a different nature in terms of the conduction mechanism. However, both mechanisms share common macroscopic features that can be expressed by a general transport equation. They are a generalisation of Ohm’s law for the density of electric current  of internal energy for thermal conduction or charge for electrical conduction, β—coefficient of proportionality of thermal or electrical conductivity, A—scalar quantity whose gradient causes a given phenomenon  [tential) .Both E and dT/dx have a gradient character, so in general we can write:2 composite, the results indirectly indicate the partial diffusion of boron into the copper matrix, which may explain the observed strong decrease in the electrical conductivity of the samples with the increase in the content of the ZrB2 phase. The easy diffusion transfer to the matrix results from the large difference in the atomic radius of copper (140 pm) and boron (85 pm). This means that boron will tend to be located in the interstitial holes of the copper lattice and cause local contraction of the crystal lattice, increasing the scattering potential of conduction electrons. At the same time, as shown by [In the case of the sintered Cu–ZrBshown by , the limA change in SPS temperature from 1123–1223 K led to an increase in the density, Young’s modulus, and hardness. The best physical and mechanical properties were obtained for the composites that were sintered at 1223 K–35 MPa.2 content on the microstructure, physical, mechanical, and electrical properties of sintered composites was studied. The results showed that the increase in the ZrB2 content in the copper matrix improves Young’s modulus and hardness while reducing the density and electrical conductivity. The addition of the reinforcing phase in an amount greater than 10 wt% negatively affects the properties of the copper matrix composites.Furthermore, the influence of the ZrB2 causes the beginning of the formation of particle conglomerates and, consequently, disturbs their homogeneous distribution in the copper matrix.The addition of 20 wt% ZrB2, as well as stabilization of the conductivity in larger amounts, indicates the partial diffusion of boron into the copper matrix.A strong decrease in the electrical conductivity of composites containing 5 and 10 wt% ZrB


Cross-sectional studies are useful for the estimation of prevalence of a particular event with concerns in specific populations, as in the case of diseases or other public health interests. Most of these studies have been carried out with binary binomial logistic regression model which estimates OR values that could be overestimated due to the adjustment of the model. Thus, the selection of the best multivariate model for cross-sectional studies is a priority to control the overestimation of the associations.We compared the precision of the estimates of the prevalence ratio (PR) of the negative Log-binomial model (NLB) with Mantel–Haenszel (MH) and the regression models Cox, Log-Poisson, Log-binomial, and the OR of the binary logistic regression in population-based cross-sectional studies. The prevalence from a previous cross-sectional study carried out in Colombia about the association of mental health disorders with the consumption of psychoactive substances  were used. The precision of the point estimates of the PR was evaluated for the NLB model with robust variance estimates, controlled with confounding variables, and confidence interval of 95%.The NLB model adjusted with robust variance showed accuracy in the measurements of crude PRs, standard errors of estimate and its corresponding confidence intervals (95%CI) as well as a high precision of the PR estimate and standard errors of estimate after the adjustment of the model by grouped age compared with the MH PR estimate.Obtained PRs and 95%CI entre NLB y MH were: cocaine consumption , marijuana consumption , cigarette smoking , alcohol consumption , and risk of consumption of psychoactive substances . The NLB model adjusted with robust variance showed mayor precision when increasing the prevalence, then the other models with robust variance with respect to MH.The NLB model with robust variance was shown as a powerful strategy for the estimation of PRs for cross-sectional population-based studies, as high precision levels were identified for point estimators, standard errors of estimate and its corresponding confidence intervals, after the adjustment of confounding variables. In addition, it does not represent convergence issues for high prevalence cases  and could be considered in cases of overdispersion and with greater precision and goodness of fit than the other models with robust variance, as it was shown with the data set of the cross-sectional study used in here. The objective of cross-sectional population-based research is to estimate prevalence of diseases or other events of interest for the human public health such as mortality, rehospitalization, quality of life, psychoactive substances consumption, among some others, and their associated (exposure) factors of these events of interest. Cross-sectional studies at the population level are usually designed with probabilistic samples with random selection, inferred or representative of the study population giving as a result unbiased, efficient, consistent, and sufficient estimators of prevalence and its corresponding 95% confidence intervals, with the estimation of standard and relative standard errors as precision indicators of the point estimates of the prevalence of the events of interest , 2.odds ratio (OR) and 95%CI as a measurement for the association of the outcome (disease or event) with potential explanatory variables. However, OR value overestimates the associations regarding to the prevalence ratios (PR = p1/p2) estimates, with an increased bias in the case of diseases or events with high prevalence [In addition, in the cross-sectional studies as there is a construction of explanatory factors of the disease or the event, it should be an adjustment of the confounding factors that could lead to misinterpretations of the results if it is not well adjusted, considering individual factors but also its possible interactions among the variables of the model , 4. For evalence –5.t of the observation, which is adjusted considering a constant time for the estimation of the prevalence ratios in the cross-sectional studies [Since 2003, Cox constant time model, Log-Poisson model, and Log-binomial regression model were proposed for controlling the bias of the overestimation of OR values in the case of binary logistic regression models, giving as a result good accuracies for the estimation of prevalence ratios (PR), although it should be evaluated the mathematical assumptions to validate these models . In the  studies .Thus, although the above-mentioned models have been used in the research field for the estimation of PRs in cross-sectional studies, there are still some issues in the models that could be improved. The negative Log-binomial regression model (NLB) has shown high mathematical consistency in the application of longitudinal cohort analytical studies and has been used in cases of overdispersion of the Poisson model –10. NLB The data used to compare the point and interval estimates of the models of the present study were taken from a previous cross-sectional population-based study, with the specific objective of estimating the prevalence of psychoactive substances consumption and its associated factors in a population of 140,000 workers in Colombia, in which a stratified random probability sample of 5810 workers was selected.The outcomes or events of interest in this study were: lifetime cocaine use, marijuana consumption in the last year, current cigarette consumption, lifetime alcohol consumption risk of consumption of psychoactive substances. The association factor used in the model was depression measured with the Zung test and grouped ages were used as a confounding variable with the following categories: 1) under 25, 2) between 26 and 29, 3) between 30 and 34, and 5) older than and equal to 35 years. It was used as a numerical variable as well.r  and p which is the probability of success, therefore the probability of failure is q = 1-p and the negative binomial probability distribution is as follows , therefore it is applicable in cross-sectional studies in the estimation of the prevalence of the disease or dichotomous variables of cross-sectional studies. The systematic components of the model which are the explanatory variables or associated factors Xi, numerical or categorical variables with their respective estimators (βi), standard errors and confidence intervals, which are used for the construction of the associative models of the cross-sectional studies. Finally, for the link function, in this case was the logarithm per se, which was proposed the name of "negative log-binomial" model for cross-sectional studies.In the construction of the generalized linear model (GLM) of the proposed negative log-binomial model, the three components of the GLM were taken into account: in the random component, the random variable of the dependent variable of the negative binomial model (Y), with exponential family distribution is measured in counts occurring at a time Maximum likelihood was used as the estimation method of the NLB and to compare iteratively reweighted least squares (IRLS), with Fisher scoring, Newton–Raphson and hybrid iterative optimization methods for convergence tolerances estimations or epsilon (ε) < 0.000001 or 1e-6 (ε > 0).g(μ) = ln(μ)=Xi βi,  vi=1/α, then  Yi⁄Xi =BN )as follows , the incidence rate ratio (IRR) of the binomial model was taken as the relative risk in analytical cohort studies and thus as the prevalence ratio (PR) in cross-sectional studies, as follows  calculation is an accurate estimator of the relative risk (RR) for the cases in which the prevalence of the disease is small (p < 10%) and therefore for the prevalence ratio in cross-sectional studies [odds ratio is defined as a ratio of odds  = p/q = p/1-p) [In analytical epidemiological studies, it has been shown that the  studies –10. The = p/1-p)  and the = p/1-p) .p1 and in the category without exposure p2, when evaluating the association with higher prevalence in the exposed than in the non-exposed (risk), it could be seen that In a cross-sectional study the prevalence of the disease are taken, in the category of exposure p < 10%) and increases with higher prevalence of the disease or event of interest [This inherent bias is controlled when the prevalence interest .Crude prevalence ratios (PR) and standard errors of estimation were considered as the reference measures of the associations (2 × 2 tables) in conjunction with the Mantel–Haenszel (MH) stratification method to control confounding variables.The precision of the PR estimates of the regression models was measured compared with PR MH reference standard, as described in equationThe indicator of the percentage of confounding effect between the association of depression with the outcomes of legal and illegal psychoactive substances consumption was also measured controlling for the grouped age confounding factor, for both crude PR of the NLB and the other three models, and the reference PR value of MH model as indicated in Eq. This equation is also used to compare the standard error of estimation of the models with respect to the standard error of MH.The PR, standard errors of estimation and 95% confidence intervals with and without robust variance adjustment of the NLB model were compared with the three models  and with the unconditional logistic regression model with and without robust variance adjusted by age, with both grouped and numerical variable. Estimations were performed in STATA 15.0  and SPSSIn the cross-sectional study of mental health and psychoactive substance consumption, a probabilistic, stratified random sample with proportional allocation was designed in 5810 workers in Colombia. The age of the workers varied between 18 and 56 years, with an average of 28.2 ± 7.1 years (median = 27.0 years) and age groups of ≤ 25 years (41.9%), 26 to 29 years (24.0%), 30 to 34 years (14.0%) and 35 and over (20.2%), with a predominance of male gender (93.4%), single marital status (48.8%), followed by married (30.0%).In this cross-sectional study the consumption of psychoactive substances was measured, estimating a lifetime prevalence of cocaine consumption of 1.8% CI 95% (1.4% -2.1%), prevalence of marijuana consumption of 9.6% CI 95%:(8.8%- 10.3%), prevalence of cigarette consumption of 21.3% CI 95%: (20.1%- 22.4%), lifetime prevalence of alcohol intake of 85.7% CI 95%:(84.8.0%- 86.6%) and risk of consumption of psychoactive substances of 96.1% CI 95%: (95.6%- 96.6%).The inherent bias of crude OR versus crude PR was increased the overestimation by higher prevalence of consumptions; for cocaine 1.2%, marijuana 7.9%, cigarette 17.5%, alcohol 133.3% and risk of consumption of psychoactive substances 233.3%, the overestimation of the association of the OR versus the PR being very high in the last two cases due to their high prevalence. The OR and PR estimators of association were different in the 5 outcomes, the overestimation of the OR being greater as the prevalence increases  stratification method, comparing with the estimation of the PR of the three models, the differences were less than 1% in the five outcomes, using Eq. The estimated prevalence ratio of the association between depressive symptoms with the different prevalence of psychoactive substance consumption in the study with the negative log-binomial model with and without robust variance adjustment were equal to the crude PR Table .The prevalence ratio of the association of depressive symptoms controlling for confounding variable by grouped age with the five outcomes showed very high precision with respect to the MH PR, measured with the Eq. The standard errors of estimation of the NLB model showed greater precision when adjusted with robust variance, showing similar standard errors and 95% confidence intervals for the five outcomes, compared with 95% CIs using the MH stratification method. Using the Bayesian BIC indicator, the NLB showed to be the best model with smaller values than the other models with robust variance. Fig. , Table 2The standard errors of PR estimation showed high precision in the robust Cox/Poisson and NLB models with respect to MH, for the 5 consumption outcomes , with the robust binomial model. showed very large differences in prevalence (85.7% and 96.1%), the standard error of estimation being higher in alcohol consumption and no convergence was found to calculate the risk of consumption of psychoactive substances estimator , the robust log binomial model showed lower precision with a higher standard error of estimate compared to the other models with robust variance and in the highest prevalence of the 5 outcomes (96.1%), no convergence was found to calculate the estimators, neither when age was adjusted categorically, nor numerically Tables  and 3. bThe unconditional binary logistic regression model has been used for the construction of the explanatory associative models of the events of interest in cross-sectional studies of different epidemiological investigations –5. HowevIn estimated prevalence less than 10%, it is expected that the inherent overestimation bias of OR versus PR was minimal in the cases of smaller prevalence of the disease . In thisIn studies since 2003 and 2008, several explanatory models were proposed for the estimation of the PR and solved the overestimation of the OR of binary logistic regression models . Among tIn this study we found concordant results with the 2003 and 2008 studies, in the crude estimates and in the control of confounding variables with the PR and their 95% CIs, as well as in the respective standard errors, in which the joint conclusion of these studies is that Cox constant time model and Log-Poisson regression with robust variance give as a result really accurate estimates for the PRs and its standard errors for the estimations in cross-sectional studies , 13–17, In the previous studies, issues related with the estimations and mathematical models were identified for the three methods. In the Log-binomial generalized linear model, due to non-convergence in the outcomes with very high prevalence, outcomes in the estimates of the PR and in its standard errors for this GLM model are performed with the maximum likelihood estimation method using iterative methods to reach estimates with convergence tolerances with epsilon (ε) less than 0.000001. In our study, the log binomial model with robust variance estimated a very high standard error compared to high prevalence such as alcohol, compared to the Cox/Poisson and NLB models with robust variance, and without convergence to obtain the PR estimators, for the risk of consumption of psychoactive substances, which has a high prevalence of 96.1%.Also, the non-convergence in the numerical confounding variables was solved, controlled with the abovementioned estimation and optimization methods, available in the statistical software such as STATA version 15 and later, in high prevalence as in our study that found convergence for the prevalence of alcohol of 85.7%, although this was not the case for very high prevalence, such as the risk of consumption of psychoactive substances of 96.1%, which did not generate convergence to obtain the estimates of the PR .For the overdispersion (extra-Poisson variance), the adjustment with robust variance proposed by Lin and Wei  was the The negative Log-binomial (NLB) regression model, which was the GLM proposed model in this study, showed accuracy with respect to the crude values of PR, standard errors and 95% CI, with the adjustment of robust variance for the standard errors’ estimations. In the case of adjustment and control of confounding variable of grouped age, results showed a very high precision with those obtained with the MH stratification method, as well as for the estimations of PR, standard errors and 95% CI with the Cox constant time model, Log-Poisson, and Log-binomial regression models when adjusted with robust variance. Very concordant results were obtained for the associations between depressive symptoms with the five psychoactive substances consumption, controlling for the numerical age, for the estimates obtained with the three available models with the adjustment for robust variance.The NLB model with robust variance adjustment is optimal in epidemiological cross-sectional studies through surveys and in some cases with clinical approaches, to estimate the prevalence of a particular disease or event of interest and its associated factors through the multivariate NLB model with robust variance adjustment, without bias of overestimation in the associations and with high accuracy for the estimates. It allows the construction of associative models to identify the groups with the highest risk of the disease or event of interest within a population. The use of NLB model could also be applied for the development of prevention and control programs for specific conditions, and in the future to decrease the prevalence of those particular conditions. Also, it could impact policy makers and decision-making for the control or follow-up of the conditions of interest within a population with high prevalence values.The negative log-binomial generalized linear model with robust variance is an optimal multivariate model for the construction of explanatory associated factors of disease or binary events of interest in cross-sectional studies, generating estimates with very high precision of the prevalence ratio, standard errors of estimation and confidence intervals, when adjusting for categorical and numerical confounding variables. This NLB model is mathematically constructed to identify the variance that could not be explained by the Poisson model in cases of overdispersion, and thus, NLB model is proposed as an alternative for those cases of overdispersion. Finally, the NLB model does not present convergence issues in the estimates of the PR and the standard errors of PR estimation, in large or small prevalence in cross-sectional studies. NLB model is proposed as a novel alternative for the analyses of prevalence ratios in cross-sectional studies, independent of high or low prevalence of the disease or the event of concern and with greater precision than the other models with robust variance with respect to MH and with the BIC Bayesian indicator, as it was shown in the current data set of this cross-sectional study.


In this study, the basalt fiber content  and replacement ratio of recycled coarse aggregate  were used as parameters, and the compressive strength of 15 cubes and 15 prisms was analyzed. The failure morphology of the specimens was characterized, and the cubic compressive strength, axial compressive strength, elastic modulus, Poisson’s ratio, and other mechanical property indices of the specimens were measured. Upon increasing the replacement ratio, the degree of damage of the specimens gradually increased, whereas the cubic compressive strength, axial compressive strength, and elastic modulus gradually decreased. As the replacement ratio was increased from 50% to 100%, the cubic compressive strength and elastic modulus were noted to decrease the most by about 9.07% and 9.87%, respectively. On the other hand, the Poisson’s ratio first decreased, followed by an increase. Upon increasing the fiber content, the degree of damage of the specimens was gradually reduced, whereas the cubic compressive strength, axial compressive strength, and elastic modulus gradually increased. As the fiber content increased from 0.075% to 0.15%, the axial compressive strength and elastic modulus increased the most by about 6.65% and 10.19%, respectively. On the other hand, the Poisson’s ratio gradually decreased. Based on the test data, the functional relationships between the strength indices and different variables, as well as the conversion value of each strength index and different variables were established; after comparison and verification, the formula calculation results were found to be in good agreement with the test results. The microstructural changes in the basalt fiber reinforced recycled aggregate concrete were characterized by scanning electron microscopy (SEM), and the changes in the mechanical properties of the basalt fiber reinforced recycled aggregate concrete as well as the mechanism of fiber modification and reinforcement were explained from a micro perspective. With the acceleration of urbanization, an increasing number of buildings have been demolished, thus resulting in a large amount of construction waste. Simultaneously, the construction of new buildings requires the use of a large amount of natural resources and construction materials. The large resource consumption inevitably causes a significant damage to the environment. Thus, it is of vital concern to effectively deal with waste concrete ,2,3,4. R3 and 2 kg/m3, upon increasing of the recycled coarse aggregate (RCA) replacement ratio, the axial compressive strength first increased followed by a decrease. Furthermore, the maximum axial compressive strength was obtained as the RCA replacement ratio was 50%. Fang et al. [Basalt fiber (BF) represents a green concrete reinforcing material. Compared with the glass fiber ,18, steeg et al.  reportedg et al.  observedOverall, the literature studies show that the mechanical properties of RAC can be improved by fiber modification. However, only a handful of studies have simultaneously focused on the BFRRAC mechanical properties and microstructure, and only failure modes and test results have been described in most studies and calculation formulas for BFRRAC are rarely proposed. This study aims to close the gap in the literature while providing important outcomes about BFRRAC regarding mechanical properties, and to propose a constitutive relationship suitable for BFRRAC. For this purpose, the mechanical properties of RAC have been studied with BF content and RCA replacement ratio as the variables. At the same time, the characteristics of BFRRAC have been analyzed by SEM after compression failure. The functional relationships between the strength indices and different variables, as well as the conversion value of each strength index and different variables have been established, which provides reference for further research and applications of BFRRAC.3 and 2300 kg/m3, respectively, and the fineness modulus range was 1.6~2.2. Grade II fly ash produced by a power plant in Gongyi City was used in this study. The basalt fibers are shown in The following materials were used to fabricate the BFRRAC specimens: cement, natural coarse aggregate, recycled coarse aggregate, natural fine aggregate, BF, high-performance polycarboxylic acid superplasticizer, and tap water. Among these, P·O 42.5 Ordinary Portland Cement was selected, and the quality indexes are shown in 3, 2 kg/m3, and 4 kg/m3 . The design of mixture proportions is presented in The RCA replacement ratios were selected to be 0%, 50%, and 100% , and the BF content was varied as 0 kg/mAn electro-hydraulic servo pressure testing machine (WAW-2000) with a maximum test force of 5000 kN was used. The cubic and axial compressive strength tests were carried out per “Standard for test methods of concrete physical and mechanical properties”  , with a F0 was 0.5 MPa, and the maximum preload value Fa was 1/3 of the axial compressive strength of the specimen. After the preload was centered, three repeated preloadings were performed between F0 and Fa. When loading to F0 and Fa, the dead load was 60 s, and the deformation value of each measuring point was recorded, and then the elastic modulus was calculated. The test loading method of elastic modulus is shown in The cubic compression failure process of BFRRAC specimens was roughly similar to that of the ordinary concrete specimens. At the initial stages of specimen loading, the specimen mainly resisted the increase in the external load by the overall elastic deformation, and the surface had no obvious change. As the load was increased gradually, cracks began to appear in the stress concentration area inside the specimen. Subsequently, the original micro-cracks of the RCA began to develop and increase. As the load continued to increase, the crackling sound of the colloidal cracking appeared, with the expansion of the internal cracks of the specimen. As a result, several vertical cracks appeared in the middle of the side in the direction 45~60°, and the surface of the BFRRAC began to bulge and peel. Upon reaching the ultimate load value, the specimen was eventually destroyed, and the cubic compression of the BFRRAC specimen exhibited a quadrangular pyramid failure morphology, as shown in At the initial stages of specimen loading, the surface of the BFRRAC prism did not exhibit any obvious change. As the load increased gradually, the specimen expanded laterally, and the original micro-cracks existing in the RCA began to develop. Furthermore, the micro-cracks between the new/old mortar and RCA began to expand upon increasing the load. BF distributed randomly inside the specimen could alleviate the stress concentration at the crack tip, thus preventing the crack propagation to a certain extent and balancing the internal force. As a result, the generation and development of cracks tended to be relatively stable. As the load continued to increase, the width and number of cracks increased sharply. The shear stress in the 45° direction reached the limit value, and the specimen exhibited the shear slip failure along the oblique section. A fraction of concrete fell off, and the internal aggregate was exposed, thus the bearing capacity was reduced. At this stage, the cracks were unstable and exhibited a sustainable development without increasing the external load. Afterwards, upon increasing the external load, the bonding between the cement mortar at the main crack, aggregate, and BF was lost, and the friction bite force on the slip surface was basically exhausted. Finally, the specimen completely lost its bearing capacity. The morphology of the axial compression of the BFRRAC specimen is shown in The compression property indices of BFRRAC are shown in 3 BF content, at a BF content of 2 kg/m3 with the RCA replacement ratios changed to 0% and 100%, the cubic compressive strength increased by 4.14% and decreased by 9.07%, respectively, whereas the axial compressive strength increased by 14.96% and decreased by 10.80%, respectively. Wang et al. [3 and 4 kg/m3, and the cubic compressive strength decreased by 4.34% and increased by 2.37%, respectively, whereas the axial compressive strength decreased by 3.32% and increased by 6.65%, respectively. The observed phenomenon was attributed to the loading process, which enhanced the axial deformation of the specimen and the bridging effect of BF effectively prevented the expansion of the cracks, thus the strength of the specimen was improved. In summary, the cubic and axial compressive strength of BFRRAC decreased upon increasing the RCA replacement ratio, whereas these exhibited an increase with BF content. Moreover, changing the RCA replacement ratio had a greater impact on the compressive strength of the specimens than the BF content.The cubic and axial compressive strength of BFRRAC as a function of different variables are shown in g et al.  and Zheng et al.  also proγ, the BF content is represented by λ, fγcu, represents the cubic compressive strength values of BFRRAC with a BF content of 2 kg/m3 under different RCA replacement ratios, facu, represents the cubic compressive strength value of BFRRAC at a BF content of 2 kg/m3 and a RCA replacement ratio of 0%, fλcu, represents the cubic compressive strength values of BFRRAC with a RCA replacement ratio of 50% under different BF contents, and fbcu, represents the cubic compressive strength of BFRRAC at a BF content of 0 kg/m3 and a RCA replacement ratio of 50%.Based on the measured values in fγc, represents the axial compressive strength values of BFRRAC at a BF content of 2 kg/m3 under different RCA replacement ratios, fac, represents the axial compressive strength of BFRRAC at a BF content of 2 kg/m3 and a RCA replacement ratio of 0%, fλc, represents the axial compressive strengths of BFRRAC at a RCA replacement ratio of 50% under different BF contents, and fbc, represents the axial compressive strength of BFRRAC at a BF content of 0 kg/m3 and a RCA replacement ratio of 50%.Based on the measured values in fγc, and fγcu, represent the axial and cubic compressive strength values of BFRRAC at a BF content of 2 kg/m3 BF under different RCA replacement ratios, fλc, and fλcu, represent the axial and the cubic compressive strength values of BFRRAC at an RCA replacement ratio of 50% under different BF contents.Because of the influence of the BF content and replacement ratio, the conversion relationship between the cubic and axial compressive strength of the ordinary concrete is no longer applicable to RAC. Therefore, the relation between the cubic and the axial compressive strength of the specimen was subjected to fitting, as shown in fc/fcu test result and the calculation result based on Equations (5) and (6) is shown in To further verify the applicability of the calculation formula, the compressive strength of specimens under different BF contents ,39,41,423, at a BF content of 2 kg/m3 with the RCA replacement ratios changed to 0% and 100%, the elastic modulus increased by 6.69% and decreased by 9.87%, respectively, whereas the Poisson’s ratio increased by 10% and 15%, respectively. At an RCA replacement ratio of 50% with the BF content changed to 0 kg/m3 and 4 kg/m3, the elastic modulus decreased by 7.01% and increased by 10.19%, respectively, whereas the Poisson’s ratio increased by 15% and decreased by 10%, respectively. In summary, upon increasing the RCA replacement ratio, the elastic modulus of BFRRAC decreased, whereas the Poisson’s ratio first decreased, followed by an increase. This was mainly due to a large number of micro-cracks inside RCA, thus it was easy to expand the crack during the test, and the density of concrete was reduced due to the adhesion of loose and porous old mortar outside RCA. Upon increasing the BF content, the elastic modulus of the prepared BFRRAC gradually increased, while the Poisson’s ratio was observed to decrease. The observed phenomenon was due to the reason that RCA adhered to the old mortar, which enhanced the friction force and mechanical bite force between the BF and mortar matrix. The distribution of BF in BFRRAC was disordered in three dimensions, which played a role in pulling the aggregate and preventing the crack propagation, thereby reducing the lateral deformation of the specimens and reducing the Poisson’s ratio. BF was noted to have an optimal compatibility with RAC. Upon incorporating a certain amount of BF, the compactness of the specimen and the continuity of the matrix increased, thus the impact of the original damage caused by crushing decreased, which enhanced the elastic modulus of the specimen.The elastic modulus and Poisson’s ratio of BFRRAC as a function of different variables are shown in The elastic modulus is a vital index reflecting the deformation ability of the materials. The elastic modulus of BFRRAC has been studied in many literature studies ,41. HoweEcc) of BFRRAC. The fitting curves of (Ec) and (Ecc) as a function of different parameters are shown in Ecc value than Ec. Obviously, the current code was not applicable to the calculation of the elastic modulus of BFRRAC, and Ec/Ecc showed a linear increasing trend with the RAC replacement ratio and BF content. Under the condition of a single parameter change (either replacement ratio or BF content), by using the least squares method, Equations (8) and (9), respectively, were obtained:Eγc, represents the calculated elastic modulus of BFRRAC with a BF content of 2 kg/m3 under different RCA replacement ratios, and Eλc, represents the calculated elastic modulus of BFRRAC with an RCA replacement ratio 50% under different BF contents.The measured data were substituted in Equation (7) to obtain the calculated elastic modulus (Ec based on Equations (8) and (9) is shown in To further verify the applicability of the calculation formula, the specimen data under different BF contents ,35,39,41p-values indicate the significance of the test parameter on the cubic and axial compressive strength. When the p-value was less than 5%, the parameter had a significant effect on the cubic and axial compressive strength. The contribution ratio represented the degree of response of each influencing factor to the dependent variable. According to the statistical analysis results, the contribution of the BF fiber content replacement ratio of the recycled coarse aggregate could be underestimated when compared with the contribution of the replacement ratio of the recycled coarse aggregate.The significance and primary and secondary order of the influence of each factor on the performance index were reflected by the analysis of variance (ANOVA). In addition, the influence relationship and law of each factor on the performance index were analyzed. In this study, the analysis was performed at a 5% level of significance to identify the statistically significant experimental parameters. For this, the data presented in The SEM analysis of BFRRAC is presented in As shown in The micromorphologies of the interfacial transition zone (ITZ) between RCA or NCA and mortar matrix are shown in As shown in The morphology of the cubic specimens in each group under compression were noted to be similar, representing quadrangular pyramid failure. The BFRRAC prisms in each group represented typical oblique section shear failure, and the incorporation of BF enhanced the integrity of each specimen after failure.3 to 4 kg/m3, the axial compressive strength increased the most, by about 6.65%. In addition, the influence of the RAC replacement ratio on the compressive strength of the specimens was noted to be greater than that of the BF content.The cubic and axial compressive strength of BFRRAC decreased upon increasing the RCA replacement ratio, whereas these increased with the BF content. As the replacement ratio was increased from 50% to 100%, the cubic compressive strength was noted to decrease the most, by about 9.07%. As the fiber content was increased from 2 kg/m3 to 4 kg/m3, the elastic modulus increased the most by about 10.19%.Upon increasing the RCA replacement ratio, the elastic modulus of BFRRAC decreased, whereas the Poisson’s ratio first decreased followed by an increase. As the replacement ratio was increased from 50% to 100%, the elastic modulus was noted to decrease the most, by about 9.87%. Upon increasing the BF content, the elastic modulus of BFRRAC increased, and the Poisson’s ratio decreased. As the fiber content was increased from 2 kg/mBased on the experiment data, the functional relationships between the strength indices and different variables as well as the conversion value of each strength index and different variables were established. In addition, by comparing the test data in the literature, the formula calculation results were in good agreement with the test results and could provide guidance for future applications in engineering.The micromorphology of the mortar matrix and ITZ, as well as the modification mechanism of BF directly affected the macroscopic mechanical properties of RAC. The mechanical properties of RAC could be optimized by the bridging and crack resistance mechanism of BF.Overall, this study carried out the mechanical properties test and microscopy analysis of BFRRAC, and established the relationship between different parameters and BFRRAC. In the future, we can continue to carry out in-depth research on this idea: Visualization of fiber distribution and pore structure distribution of RAC is studied by numerical simulation software and the three-dimensional microscopic analysis of dynamic and static mechanical properties of BFRRAC.This study investigated the basic mechanical properties of BFRRAC at the macroscopic and microscopic levels, along with discussing the influence of the RCA replacement ratio and BF content on the compressive failure morphology, strength, and deformation of BFRRAC. The main conclusions were as follows: