WC Phase Research Articles

Study of metal–ceramic WC/Cu nano-wear behavior and strengthening mechanism

In view of the inherent poor tribological properties of copper, the reinforcement of copper matrix composites with WC particles presents a promising research area with significant industrial influence. Therefore, in the present study, a molecular dynamics approach is used to simulate the process of repeated friction of diamond grinding balls on WC/Cu composites, and the friction force, friction coefficient, abrasion depth, wear rate, abrasion morphology, von-Mises stress, internal defects, workpiece energy, and performance comparison of different layer thicknesses are systematically investigated in the multiple friction process. It is found that the fluctuation amplitude of friction force, friction coefficient, and abrasion depth are smaller and the fluctuation frequency is larger during the initial friction, whereas near the WC phase, there appears extreme values of the above parameters and the von-Mises stress is highly concentrated while the workpiece energy contonues to increase. In the case of the repeated friction, with the increase of friction times, the friction force, friction coefficient, and abrasion depth fluctuation amplitude increase, the fluctuation frequency decreases, the workpiece energy reaches an extreme value near the WC phase, and a large number of dislocations plug, therefore, the region is strengthened. As the distance between the grinding ball and the WC phase decreases, the more obvious the strengthening effect, the stronger the ability of workpiece to resist the wear will be.

Theoretical investigation of compressed hexagonal and rock-salt structures of molybdenum and chromium carbides

This research paper reports the structural, electronic, elastic anisotropy, and thermodynamic characteristics of Molybdenum and Chromium Carbides (MoC and CrC) at zero and under high pressures. We consider both hexagonal tungsten carbide phase (WC) and rock-salt (NaCl) structures. Our investigation is performed using the first-principles pseudo-potential plane waves method. The fundamental ground state is the hexagonal (WC) phase for MoC and CrC compounds. MoC is relatively more ionic than CrC. The investigated materials are brittle in the WC phase and ductile in the RS phase for pressures below 30 GPa. MoC and CrC are hard materials and anisotropic in sound velocity. Phonon spectra are reported for both compounds in a WC and NaCl at zero-pressure and high pressures. Ideal stoichiometric WC crystals of MoC and CrC are predicted to be dynamically stable. The pressure and temperature dependence of various macroscopic thermodynamic parameters of MoC and CrC compounds are also discussed.

Investigation of ultrafine WC–Co–Fe–Ni–Cr3C2 cemented carbide microstructure and properties based on phase diagram thermodynamics

Abstract In this work, different Fe/Ni ratios with constant Co content were prepared to explore microstructure and properties of ultrafine WC-10 wt.%(Co–Fe–Ni)-Cr3C2 cemented carbides. The increase in Fe content in binder has difficulty in controlling carbon content. Therefore, the carbon window was determined by phase diagram to prepare carbon-balanced cemented carbides. The increase in Fe/Ni ratio in the binder deteriorates the uniformity of the binder phase distribution and refines the WC and binder phase grains by affecting the solubility of WC in binder and the wettability of the binder. Grain size, microstructural irregularities and solid solution strengthening of binder phase affect the mechanical properties of cemented carbides. The relative density of cemented carbide with Fe/Ni = 30:70 in the binder is 99.8 % and the transverse fracture strength is 2449 MPa maximum, but the fracture toughness is slightly low. Because of the passivation characteristics of Ni, the alloy with Fe/Ni = 0:100 in the binder has better resistance to corrosion resistance.

Effects of TiC0.4 on microstructure and properties of WC composites

WC composites with 5 wt% TiC0.4 were fabricated by spark plasma sintering (SPS) at sintering temperature of 1400–1700 °C for 10 min under an external pressure of 50 MPa. It can be observed that the WC-5 wt% TiC0.4 composites mainly consisted of WC phase and non-stoichiometric (W1−x, Tix)Cn solid solution phase and the amount of WC dissolving in TiC0.4 increased with sintering temperature. The (W1−x, Tix)Cn solid solutions uniformly distributed around WC grains and formed a semi-coherency interface with WC, which restricted the growth of WC grains and enhanced mechanical properties of the WC-5 wt% TiC0.4 composites. The average grain size of WC (251.5 ± 201.6 nm) in WC-5 wt% TiC0.4 composite sintered at 1600 ℃ was considerably smaller compared to most of previously reported WC-based composites. The existence of high content of C vacancies in non-stoichiometric TiC0.4 raised remarkably the diffusion rate of W and Ti atoms in the sintering process of WC-5 wt% TiC0.4 composites in contrast with stoichiometric TiC. The WC-5 wt% TiC0.4 composite sintered at 1600 ℃ possessed the optimum properties, with the hardness of 21.9 GPa, fracture toughness of 7.6 MPa·m1/2, flexural strength of 612 MPa and compressive strength of 2.7 GPa. Moreover, it can be confirmed that the oxidation resistance of WC-5 wt% TiC0.4 composite at higher temperature outperformed that below 1218 ℃. In addition, the WC-5 wt% TiC0.4 composite sintered at 1600 ℃ showed higher high-temperature hardness, lower thermal conductivity and better resistance to oxidation than those of conventional WC-Co composites.

Preparation of high wear resistance nickel based WC coating by carefully adjusting interface structure

In recent years, many scholars have paid attention to wear-resistant coatings for shield machine cutterheads due to their very high consumption rates. Among these coatings, nickel-based tungsten carbide (Ni-based WC) is one of the best, showing both corrosion resistance and wear resistance. However, to further improve the wear resistance of such coatings, there are still numerous issues that need to be resolved. Herein, a new method, distinct from conventional methods, is presented. Specifically, the brittle phase W2C is not widely regarded as the main wear-resistant phase, but we were surprised to find that careful adjustment of its rigid structure can yield satisfactory results. Experimental results and first-principles simulations have indicated that the friction coefficient and weight loss of a coating with a suitable distribution of W2C are only half of those of a traditional Ni-based WC coating (about five times higher than those of the substrate), which can mainly be attributed to the excellent thermal expansion coefficient and hardness of the W2C phase. As we expected, the surface morphology of the material after wear revealed that the suitable W2C layer has a well-defined friction morphology. We hope to provide new ideas for the study of Ni-based WC coatings in shield machine cutterheads.

Effect of abrasive particle size on the tribological behavior of thermal sprayed WC-Cr3C2-Ni coatings

In order to improve the wear performance of ball mill liners, two types of WC-Cr3C2-12Ni coatings with different Cr3C2 contents were prepared based on high- velocity oxygen fuel (HVOF) spraying technology. The three-body abrasive wear behavior of the WC-10Cr3C2-12Ni (W10N) and WC-30Cr3C2-12Ni (W30N) protective coatings under different particle sizes was systematically evaluated. Results show that the phase composition, microstructure, and mechanical properties of WC-Cr3C2-12Ni coatings were influenced by Cr3C2 content. A large amount of WC phase with good dispersion and fine morphology must be maintained to improve the wear resistance of the coatings. The friction coefficient of both coatings was the lowest when the abrasive particle size was 12.0 µm, but it was still lower than under the no-particle condition. In addition, the friction coefficient of the W30N coatings fluctuated when the particle size were 1.5 and 4.0 µm. The primary wear mechanisms of the two coatings without particles were oxidation wear and fatigue wear, respectively, and the microstructure unevenness and low WC volume fraction led to serious wear of the W30N coatings by preferential removal of the binder phase and pull-out of the WC. The wear mechanisms of the coatings after adding small to large particles were as follows: abrasive particles protected the coatings; rounded the WC grains; and planed the coating to exfoliate in layers. By contrast, the wear resistance of the W10N coatings was obviously superior to that of the W30N coatings. Importantly, the particle size influenced the counter-balls more than the coatings. This study provides potential applications for the surface protection and life extension of ball mill liners.

Microstructure and Wear Property of Graphene Nanoplatelets Reinforced Nickel-Based Composite Coating by Laser Cladding

Nickel-based composite coatings containing graphene nanoplatelets (GNPs) were prepared on Q235 steel using laser cladding. In order to retain the multilayer GNPs in the composite coatings after laser cladding, NiGNPs were prepared by electroless nickel plating on GNPs as the additive phase. All the coatings contain γ-(Ni, Fe), Cr23C6, Cr7C3, Fe3C and WC phases, and multilayer GNPs were retained successfully in the composite coatings. With the addition of GNPs, the microstructure of the coatings was obviously refined and the content of Cr-C compounds were increased along with its changed morphology. The mean microhardness of the Ni-based composite coatings containing GNPs was significantly improved compared to that of Ni45 coating, and the maximum microhardness was 745.06 when 20% NiGNPs was added. The results indicated that, due to the refinement and lubricating effects of GNPs, the friction coefficients of composite coatings were reduced and the wear resistance was improved compared to Ni45 coating.

High temperature wear resistance of tungsten carbide particle reinforced intermetallic compound matrix composite by in-situ thermite reaction

Tungsten carbide (WC) particle reinforced Ni3Al intermetallic matrix composites (WC–Ni3Al) was first fabricated by in situ thermite reaction. The microstructure and high temperature wear resistance of the WC-Ni3Al composite have been studied. The WC-Ni3Al composite contains Ni3Al, WC and B2 phases, and the volume fraction of Ni3Al, WC and B2 were 55.27%, 10.67% and 34.06%, respectively. The WC-Ni3Al composite exhibits excellent friction and wear resistance. Our findings have important engineering implications for the preparation of intermetallic matrix composites.

Metallurgical and machining performance aspects of cryotreated tungsten carbide micro-end mill cutters

Demand for miniaturized parts with tight geometrical tolerances and superior surface finish has been increasing. Development of micromachining processes has enabled adaptation of miniaturized parts and products in mechanical systems. Machining at the microscale level has supplementary challenges like high cutting forces, reduced tool life, and damaged machined surfaces. Catastrophic failure of microtools is notable problem, if tool deflection increases significantly. Therefore, incorporating tool life improvement measures are essential to minimize tool replacement cost and also to achieve efficient cutting at micro-level. Cryotreatment imparts better physical properties to cutting tools. In the present work, effects of different cryogenic treatment parameters on micro tungsten carbide-cobalt (WC-Co) end mill cutters and its performance while machining Ti-6Al-4V have been investigated. The metallurgical changes imparted to cutting tool by cryotreatment are studied via micro-hardness test along with EDS, SEM and XRD methods. It is found that all cryotreated tools have higher hardness compared to untreated tools. Additional η (eta) carbide formation has been clearly observed for the tools soaked for 24 h, moreover a variation in other phase of WC is also observed for different set of cryotreatment. Machining process is significantly affected by the low thermal conductivity of Ti-6Al-4V. In case of untreated micro-milling tool, abrasive wear is dominant, whereas built-up-edge affected the performance of cryotreated tools at shallow cryotreatment temperatures for 8–16 h soaking time. Deep cryotreated tool (at 24 h soaking time) performed better in terms of cutting force and surface roughness due to retainment of sharp cutting edge.

Preparation and in-situ strengthening mechanisms of Mo composites with the addition of WC

The strength enhancement is critical for the application exploration of Mo-based materials. In this work, a secondary phase of WC is introduced into the Mo matrix, and the corresponding phase, microstructure and mechanical properties have been studied. It is found that the addition of WC particles can significantly improve the mechanical properties, leading to a high ultimate tensile strength (UTS) of 591.5 MPa and a hardness of 242.7 HV over the sintered Mo–12%WC composite, which are about 21.2% and 49.5% higher than those of pure Mo, respectively. During the sintering, the additive WC particles react with the Mo matrix to in-situ generate W and Mo2C, and the former is dissolved into the Mo matrix to exhibit solid solution strengthening. Besides, the latter hinders the migration of grain boundaries (GBs) to limit the grain growth of Mo, resulting in smaller grain size. More importantly, the Mo2C (1‾2‾1) can gain coherent interfaces with Mo (11‾ 0) to intensify the phase boundary. This work paves a way for the design of high-performance composites through the in-situ reinforcement of decomposable additives.

Impact of Ce2O3 on microstructure and properties of matrix-body for PDC drill bits synthesized via pressureless melt infiltration

The materials of matrix-body polycrystalline diamond composite (PDC) bits were fabricated through pressureless melt infiltration method at 1200 °C for 1 h within vacuum furnace using molten CuNi metallic binder, Ni and WC powders (including cast WC, spherical WC, and fine WC). Various weight ratios of Ce2O3/(WC + Ni + CuNi) ranging from 0 to 0.01 were added to matrix-body materials. The influence of Ce2O3 on the microstructure, phase formation, phase transformations, and related mechanical properties of matrix-body materials was thoroughly investigated. The results show that experimental temperature led to the decomposition of WC and partial dissolution of W and C in CuNi binder alloys. In matrix-body materials with no Ce2O3 addition, only new W2C phase was formed. With further increase in Ce2O3/(WC + Ni + CuNi) ratios, spherical WC was dispersed into smaller WC particles. Meanwhile, new phases (namely Ni2W4C, C, and W2C) were found. The material exhibited an optimal hardness (HRA = 93.7) and transverse rupture strength (1846.8 MPa) when Ce2O3/(WC + Ni + CuNi) ratio was 0.006. However, impact toughness was slightly decreased, while the highest value of 6.45 J cm−2 was measured for the sample with Ce2O3/(WC + Ni + CuNi) ratio of 0.01.

Microstructure and diametral fracture strength of spark plasma sintered WC-6Co-0.2B and WC-6Co-0.5B ceramic composites from nanosized and metastable WC powders

The present work aimed at evaluating the microstructures and mechanical properties of spark plasma sintered WC-6 wt% Co ceramic composites doped with boron (0.2 and 0.5 wt%). W-50 at% C (W-6.13 wt% C) powders produced under different milling times (20, 60, 180, and 600 min) were used as starting materials and subsequently mixed with Co (6 wt%) and B (0.2 or 0.5 wt%) powders for 5 min. The resultant WC-Co-B powder mixtures were consolidated by spark plasma sintering at 1450 °C for 10 min at 40 MPa under vacuum in order to obtain the samples with 10 mm diameter and 3 mm thickness. The starting powders and the sintered samples were characterized by laser diffraction particle size analysis, X-ray diffraction with Rietveld refinement, relative density, scanning electron microscopy, energy dispersive spectrometry, Vickers hardness test, and diametral compression test. Supersaturated W solid solution (WSS) with a crystallite size of <50 nm was formed in W-50C (at%) powder mixtures. The relative density of the sintered composites increased with the increasing milling time up to 180 min from 79.7%±0.6% to 86.7%±0.5% for WC-6Co-0.2B and from 86.7%±0.6% to 90.9%±0.4% for WC-6Co-0.5B. Furthermore, the WC phase appeared as the matrix in the sintered samples, and W2CoB2 precipitated homogeneously around WC grain boundaries, mainly to those containing 0.5% B. The Vickers hardness values of the sintered WC-6Co-0.2B and WC-6Co-0.5B ranged from 1790±39 to 2158±25 HV and 1858±31 to 2182±28 HV, respectively. The fracture strength (determined by diametral compression test) varied between 144-353 MPa due to the porosity and precipitates in thin-thickness cylinder samples.

Effect of WC content on microstructure and properties of CrFeMoNiTi(WC)x high‐entropy alloys composite coatings prepared by selective laser melting

AbstractTo improve the surface properties of Q235 carbon steels, CrFeMoNiTi(WC)x high‐entropy alloy composite coatings were fabricated via selective laser melting. The microstructure, wear resistance, and corrosion resistance of the composite coatings were studied. Spherical or near‐spherical tungsten carbide (WC) particles are dispersively distributed in the coatings, resulting in the appearance of obvious WC and TiW2C phases. And the composite coatings mainly consist of body‐centered cubic (BCC) and face‐centered cubic (FCC). When x ≤ 0.3, the addition of WC enhances the BCC diffraction peak. Microhardness of the composite coatings with WC increases and is much higher than that of the substrate (280.6 HV0.1). The hardness of the CrFeMoNiTi(WC)0.3 (1005.1 HV0.1) is the highest among the composite coatings. The retained WC particles and BCC acted as load bearers during the friction process, which reduces the wear loss of the composite coating. Also, the anodic protection caused by the corrosion‐resistant WC particles and BCC greatly improves the ability of the composite coatings to resist NaCl attack. Hence, CrFeMoNiTi(WC)0.3 exhibited the optimum wear resistance and corrosion resistance.

Effect of C content on microstructure and mechanical properties of Cr-based hard composites obtained by different sintering methods

Nanocrystalline Cr-based-WC powders with different C contents (5.59, 6.03, and 6.69 wt% C) were sintered by four different sintering methods, including liquid phase sintering (LPS), hot pressing (HP), field-assisted hot pressing (FAHP), and spark plasma sintering (SPS). The densification, average WC grain size, phase composition, microstructure, and mechanical properties of Cr-based-WC hardmetals were dependent on the C contents and the applied sintering methods. The spark plasma sintering technique was superior to the other processing methods, giving fully dense samples (99.7%) at a lower sintering temperature and a shorter sintering time. The average WC grain sizes of samples with 5.59 wt% C sintered by LPS, HP, FAHP, and SPS were 0.9 μm, 1.0 μm, 0.7 μm, and 0.1 μm, respectively, which demonstrated that Cr-based binder had a strong inhibitory effect on the growth of WC grains. Brittle carbides (M23C6/M6C) were formed and further grew in LPSed and HPed samples, while Cr2O3 phase was detected in all FAHPed and SPSed samples. C element could react with the oxides and remove them from the samples by forming gaseous species such as CO and CO2 in LPSed and HPed samples sintered for hours. On the contrary, Cr2O3 phase was formed due to the strong affinity between Cr and O during FAHP and SPS sintering process, where the densification was finished in minutes. Moreover, the C content played a key role in determining the microstructure and phase formation. Generally, M6C, M23C6, Cr7C3, and graphite phases were subsequently induced with the increase of C content from 5.59 to 6.69 wt%, which was examined by the thermodynamic simulation of W–C–Cr–Fe–O system. The mechanical properties, including hardness, fracture toughness, transverse rupture strength, and compressive strength, of Cr-based-WC hardmetals were fully investigated. All sintered Cr-based-WC hardmetals showed an obvious advantage in hardness, considering that the WC volume fraction (only 70%) was much lower than that (≥90%) of commercial Co-based WC hardmetals. Especially, SPS-1 sample had achieved amazing compressive mechanical properties (hardness of 2219 HV30, fracture toughness of 8.2 MPa m−1/2, transverse rupture strength of 531 MPa, and compressive strength of 3296 MPa), which were superior to nanosized Co-based-WC hardmetals. The microstructural evolution mechanisms during LPS and SPS were further inferred.

Microstructure evolution of the laser surface melted WC-Ni coatings exposed to cavitation erosion

In this study, WC-Ni coatings were deposited using cold spraying followed by laser surface melting to improve the cavitation erosion resistance. The remelted coating presented a three-dimensional WC skeleton structure which could be regulated. The remelted coatings with uniformly distributed WC skeleton exhibited remarkable cavitation erosion resistance. The observed microstructure evolution in the remelted coatings during cavitation erosion suggested that the WC skeleton prevented crack propagation and therefore enhanced the cavitation erosion resistance. Results also indicated that the enhanced cavitation erosion resistance of the remelted coatings was attributed to the synergistic effect of the Ni binder phase and the hard WC phase. Adjusting and controlling the structure of the coatings allowed the WC-based coatings to exhibit excellent cavitation erosion resistance.

New Low-Temperature Method of Synthesis of Boron Carbide Matrix Ceramics Ultra-Dispersive Powders and their Spark Plasma Sintering

The ultra-dispersive powders of pre-ceramic precursors for boron carbide based composites were obtained by relatively low-temperature (at 200 – 1000 °C) synthesis from liquid charges containing available compounds such as salts and oxides. Boron carbide matrix ceramics were compacted by their reactive spark plasma sintering (SPS) at 1500 – 1700 °C. It is noted that the X-ray diffraction (XRD) peaks corresponding (m)ZrO2 and WC phases presented in the synthetic pre-ceramic precursors disappear after the SPS is conducted at 1500 °C. It is established that the addition of tungsten and cobalt compounds promotes both the low-temperature synthesis of ceramic components and sintering processes of their powders. Energy dispersive X-ray (EDX) analysis showed that the ceramics contain a small amount of Co (0.8 – 2 wt.%). The density of samples of cobalt-containing ceramics B4C–ZrB2–W2B5–Co is higher compared to that of cobalt-free ceramics B4C–ZrB2–W2B5.

Study on Microstructure and Properties of Ni60A/WC Composite Coating by Alternating-Magnetic-Field-Assisted Laser Cladding.

Ni60A/WC composite coating is prepared on 45 steel substrate by alternating-magnetic-field-assisted laser cladding. We compare the effects of different magnetic field intensity on WC particle distribution, microstructure, phase composition, microhardness and wear; in addition, the mechanism of alternating magnetic fields on cladding layers is briefly analyzed. The results show that an alternating magnetic field can significantly homogenize the distribution of WC particles. WC particles at the bottom are stirred and dispersed to the middle and upper area of the laser pool. The distribution of WC in the bottom region 6 of the coating decreases from 19.1% to 10%, the distribution of WC in the bottom region 5 decreases from 46.46% to 33.3%, the WC distribution in the top region 1 of the coating increases from 0 to 7.7% and the WC distribution in the top region 2 of the coating increases from 8.08% to 12.2%. The stirring of alternating magnetic fields strengthens the solute convection in the laser pool, refines the snowflake-shaped carbide hard phase and improves the coating microhardness and wear property, and adhesive wear and abrasive wear decrease gradually with increasing magnetic field strength.

In-situ electrochemical reconstruction of tungsten carbide using Na2CO3-containing molten salt

This paper reports a novel method for rapid atomic-level reconstruction of tungsten carbide (WC) using Na2CO3-containing molten salt. Herein, WC was used as consumable anode and Na2CO3 was active species on WC anode and carbon donor. Thermodynamic calculations were used to verify the feasibility of this electrolytic method for reconstructing WC. Experimental results showed that the addition of Na2CO3 significantly enhanced dissolution efficiency of WC. Therefore, more tungsten (W) source was supplied. Electrochemical analysis demonstrated that Na2CO3 also supplied carbon by two-step reduction process, which led to the formation of WC. These experiments confirmed that cathode product was converted from W to WC by the introduction of Na2CO3 additive into molten salt. WC phase started to form at cell voltages above 2.2 V. In initial stage of reaction, carbonate was preferentially reduced in cathode region to form amorphous C. As the reaction proceeded, W ions migrated from anode and began to participate in reduction process, forming W. Finally, W was transformed to WC by carbonization process.

Microstructure and properties of WC-12Co cemented carbide fabricated via selective electron beam melting

In this study, we investigated the microstructure, mechanical and wear properties of WC-12Co cemented carbides fabricated via selective electron beam melting (SEBM). Subsequently, some of the samples were treated with vacuum sintering heat treatment at 1400 °C at 5 MPa under argon. Apart from the WC and Co phases, the Co3W3C phase was found in the SEBM-fabricated cemented carbides. After heat treatment, WC grain growth and the Co6W6C phase appeared. Interestingly, η phase content decreased after heat treatment. The longitudinal section of the samples exhibited a layered structure, which was interlaced with coarse and fine WC. A compressive strength value of 1839 MPa was achieved after heat treatment, while the compressive strength without heat treatment was 1770 MPa. The nanoindentation test showed that the microhardness of the heat-treated samples decreased compared to the SEBM- fabricated sample (18.92 GPa). The SEBM-fabricated WC-12Co cemented carbides had an average friction coefficient of 0.548 and a wear rate of 0.0055 mm3, which increased by 59.7% and 142% in the samples after heat treatment.

Microstructure and sliding wear behavior of (AlCoCrFeNi)1-x(WC)x

In this study, (AlCoCrFeNi)1-x(WC)x high-entropy alloy composites with different WC weight ratios (x = 0, 10, 30, 50 wt%) were prepared using the gas atomization method and a vacuum hot-pressing sintering technique. The phase compositions, microstructures, and tribological properties in a wide temperature domain of the (AlCoCrFeNi)1-x(WC)x composites were evaluated over a wide temperature range. The results showed that an increase in the WC weight fraction promoted the diffusion of Fe, Co, and Ni from the body-centered cubic (BCC) and face-centered cubic (FCC) phases to generate η-carbide phases containing WC. This hindered the transformation of the BCC phase to the FCC+σ phase, resulting in a decrease in the FCC content and an increase in the BCC phase. The BCC phase further decomposed into the A2+B2 phase by spinodal decomposition. At the same time, the coupling strengthening effect of the η-carbide, BCC, and WC phases resulted in a significant increase in the hardness of the (AlCoCrFeNi)1-x(WC)x composites.The characterization of the tribological properties of the (AlCoCrFeNi)1-x(WC)x composites over a wide temperature range showed that the friction coefficient decreased with the addition of WC. In addition, the (AlCoCrFeNi)1-x(WC)x composites showed good tribological properties and wear resistance at high temperatures, i.e., the wear rate of the composites decreased significantly. This can be attributed to the formation of an oxide film on the worn surface.