Pressureless sintering and tribological properties of WC–ZrO2 composites

In a recent work [Basu, B., Lee, J. H. and Kim, D. Y., Development of WC-ZrO₂ nanocomposites by spark plasma sintering. J. Am. Ceram. Soc. 2004 87(2), 317–319], the processing of ultrahard WC–ZrO₂ nanocomposites using spark plasma sintering is reported. In the present work, we investigate the processing and properties of WC–6 wt.% ZrO₂ composites, densified by pressureless sintering route. The densification of the WC–ZrO₂ composites was performed in the temperature range of 1500–1700 °C with varying time (1–3 h) in vacuum. The experimental results indicate that significantly high hardness of 22–23 GPa and moderate fracture toughness of ∼5 MPa m^1/2 can be obtained with 2 mol% Y–stabilized ZrO₂ sinter-additive, sintered at 1600 °C for 3 h. Furthermore, the friction and wear behavior of optimized WC–ZrO₂ composite is investigated on a fretting mode I wear tester. The tribological results reveal that a moderate coefficient of friction in the range from 0.15 to 0.5 can be achieved with the optimised composite. A transition in friction and wear with load is noted. The dominant mechanisms of material removal are tribochemical wear and spalling of tribolayer.     

Characterization of 1050Al/Al3Ni/ZrO2 hybrid surface composites fabricated by friction stir processing

Al/Al₃Ni and Al/nano-ZrO₂ mono and Al/Al₃Ni/ZrO₂ hybrid composites were produced by one- and four-pass friction stir processing (FSP). Then, the microstructure, hardness, and wear performance of the surface composites were evaluated. Results showed that the incorporation of Ni particles into the Al surface and their in situ reaction with the substrate resulted in the development of Al₃Ni particles in the stir zone. The formation mechanism of these particles was deeply studied from both thermodynamics and kinetics aspects. Similarly, the four-pass FSP led to the distribution of ZrO₂ nanoparticles and the formation of Al/ZrO₂ composites. With the addition of both Ni and ZrO₂ particles, a hybrid Al/Al₃Ni/ZrO₂ composite was produced. This caused a 60% improvement in hardness and a 35% improvement in wear resistance of Al substrate. In the case of monolithic composites, both abrasion and adhesion were responsible for the material removal during the wear test, whereas adhesion was specified as the dominant wear mechanism in the hybrid composite.     

Influence of WC particles on the microstructural and mechanical properties of 3 mol% Y2O3 stabilized ZrO2 matrix composites produced by hot pressing

Yttria stabilized polycrystalline tetragonal zirconia (Y-TZP)-tungsten carbide (WC) composites were fabricated by hot pressing. Yttria (Y₂O₃) stabilizer content was kept at 3 mol% to ensure the phase structure of the Y-TZP composites to be tetragonal. To increase the moderate hardness of the 3 mol% Y₂O₃ added TZP structure, hard WC particles were added with various proportions up to 40 vol%. The TZP/WC composites were sintered at different sintering temperatures between 1450 and 1550 °C.The mechanical and microstructural properties of the resulting composites as well as the phase compositions were investigated. Reciprocating pin-on-disk tests were carried out to determine the wear behavior of the Y-TZP/WC composites. Using bi-modal WC reinforcement, the performance of the composite against wear was improved. Using dry wear sliding conditions under 55 N normal load and 45 km sliding distance, the worn volume of the 75 vol% nanosized - WC distributed 3Y-TZP/40WC composite was about 0.003 mm³.     

Effect of microwave sintering on the microstructure and mechanical properties of AA7075/B4C/ZrC hybrid nano composite fabricated by powder metallurgy techniques

AA7075 + 6%B4C+3%ZrC nano hybrid composite was successfully fabricated, with nano reinforcements composition in AA7075 alloy selected based on previous investigation, to achieve better mechanical performance. Two different sintering techniques, namely conventional and microwave, were implemented to determine the effect on microstructural and mechanical properties. Microstructural investigation was performed with the help of W-SEM. Tensile, compression, and hardness were measured with the help of UTM and Vickers microhardness machine. Porosity was calculated by using Archimedes principle. It was observed that the added nano ZrC particles formed agglomerates and the B₄C particles were distributed homogenously. Composites processed by microwave sintering showed excellent mechanical properties compared to the conventionally sintered composites. No intermetallic compounds were detected in microwave sintered composites through XRD analysis, indicating strong and clean interface bonds between matrix and reinforcement particles. High strain to fracture value of 12.24% was noted in microwave sintered nano hybrid composite, while it was 6.12% for conventional sintered one. Fractography revealed no peeling action of reinforcements from the matrix material, and the mode of failure was brittle. It was concluded that, while fabricating nano range hybrid composites, the implementation of advanced sintering technique (microwave sintering) with low sintering temperatures and low sintering times with internal heat generations, helps in eliminating defects that may develop because of high surface energies of nano range reinforcements.     

Tribological and mechanical characteristics of AA5083 alloy reinforced by hybridising heavy ceramic particles Ta2C & VC with light GNP and Al2O3 nanoparticles

In this study, AA5083 sheets were reinforced with four different hybrid nanoparticles by friction stir processing (FSP) for the development of surface nanocomposites used in advanced engineering applications. The present research focused on improving the properties and tribological behaviour of AA5083 alloy surfaces, including novel hybrid nanoparticles and the intermetallic phase formed during FSP. A tribometer tester with a constant normal load was used to examine the tribological performance of the hybrid composites. After the wear test, a surface profiler inspector was used to analyse the morphology and surface roughness of the examined materials. The Vickers micro-hardness of the base metal and the manufactured composites were measured. During FSP, a new intermetallic phase of AlV₃ was successfully formed at 300–400 °C in the hybrid nanocomposites containing VC particles. The reinforcements resulted in additional grain refining than FSP. The AA5083/Ta2C–Al₂O₃ exhibited the greatest grain refinement, a sixty-fold reduction in grain size compared to that of the base alloy. The results revealed that the hybrid nanocomposites containing VC particles demonstrated the most significant microhardness values inside the stirred zone as a result of the presence of the AlV₃ phase, which was increased by 25–30%. Moreover, the mechanical properties were significantly improved for all manufactured nanocomposites. The tensile strength was increased by 28% through the hybridisation of AA5083 using a hybrid of VC-GNPs. The dispersion of Ta₂C-GNPs and VC-GNPs in the matrix led to excellent interfacial adhesion, resulting in an enhancement in the mechanical properties. The AA5083/VC-GNPs surface composite outperformed other manufactured composites regarding wear resistance. In addition, due to GNPs soft nature, it reduced the coefficient of friction (COF) of the manufactured composites by 20–25% compared to other reinforcements.     

Development of ZrO2–WC composites by pulsed electric current sintering

ZrO₂–WC ceramic composites with 40 vol% WC were consolidated by pulsed electric current sintering (PECS) for 4 min at 1450 °C under a pressure of 60 MPa. The effect of ZrO₂ stabilizers and the source of WC powder on the densification, phase constitution, microstructure and mechanical properties of the ZrO₂–WC composites were investigated and analyzed. The experimental results revealed that the amount and type of ZrO₂ stabilizers played a primary role on the phase constitution and mechanical properties of the composites in comparison to the morphology and size of the WC powder. The 2 mol% Y₂O₃-stabilized composites exhibited much better mechanical properties than that of 1.75 mol% Y₂O₃-stabilized or 1 mol% Y₂O₃ + 6 or 8 mol% CeO₂ co-stabilized composites. A Vickers hardness of 16.2 GPa, fracture toughness of 6.9 MPa m^1/2, and flexural strength of 1982 MPa were obtained for the composites PECS from a mixture of nanometer sized WC and 2 mol% Y₂O₃-stabilized ZrO₂ powder.     

Friction and wear behavior of C-based composites in situ reinforced with W2B5

The C-W₂B₅ composites with W₂B₅ content of 30 vol.% and 40 vol.% were fabricated by reaction hot pressing sintering. The mechanical properties and friction and wear behavior of the composites were investigated. For comparison, the friction and wear behavior of graphite was also studied. It was found that the presence of W₂B₅ grain resulted in notable improvements in mechanical properties and wear resistance of the composites compared to graphite in spite of a little higher friction coefficient. A graphite-rich mechanically mixed layer (MML) was formed on the worn surface of the composites, which facilitated the low friction coefficient. Fracture and removal of the MML depending on the fracture toughness of the composites and Hertzian stress levels were considered to be the main wear mechanism.     

Effect of CuO on self-lubricating properties of ZrO2(Y2O3)–Mo composites at high temperatures

In this paper, ZrO₂ matrix high-temperature self-lubricating composites with addition of CuO as lubricant were prepared using a hot-pressing method by tailoring the content of CuO. The wear and friction behaviour of the composites were investigated from 700 °C to 1000 °C. The composites sliding against an Al₂O₃ ceramic ball exhibited excellent self-lubricating and anti-wear properties at high temperatures. The low friction and wear mechanisms were investigated in detail.     

Friction and wear characteristics of ceramic particle filled polytetrafluoroethylene composites under oil-lubricated conditions

Five kinds of polytetrafluoroethylene (PTFE)-based composites were prepared: PTFE, PTFE + 30 vol % SiC, PTFE + 30 vol % Si₃N₄, PTFE + 30 vol % BN, and PTFE + 30 vol % B₂O₃. The friction and wear properties of these ceramic particle filled PTFE composites sliding against GCr15 bearing steel under both dry and liquid paraffin lubricated conditions were studied by using an MHK-500 ring-block wear tester. The worn surfaces and the transfer films formed on the surface of the GCr15 bearing steel of these PTFE composites were investigated by using a scanning electron microscope (SEM)and an optical microscope, respectively. The experimental results show that the ceramic particles of SiC, Si₃N₄, BN, and B₂O₃ can greatly reduce the wear of the PTFE composites; the wear-reducing action of Si₃N₄ is the most effective, that of SiC is the next most effective, then the BN, and that of B₂O₃ is the worst. We found that B₂O₃ reduces the friction coefficient of the PTFE composite but SiC, Si₃N₄, and BN increase the friction coefficients of the PTFE composites. However, the friction and wear properties of the ceramic particle filled PTFE composites can be greatly improved by lubrication with liquid paraffin, and the friction coefficients of the PTFE composites can be decreased by 1 order of magnitude. Under lubrication of liquid paraffin the friction coefficients of these ceramic particle filled PTFE composites decrease with an increase of load, but the wear of the PTFE composites increases with a load increase. The variations of the friction coefficients with load for these ceramic particle filled PTFE composites under lubrication of liquid paraffin can be properly described by the relationship between the friction coefficient (μ) and the simplified Sommerfeld variable N/P as given here. The investigations of the frictional surfaces show that the ceramic particles SiC, Si₃N₄, BN, and B₂O₃ enhance the adhesion of the transfer films of the PTFE composites to the surface of GCr15 bearing steel, so they greatly reduce the wear of the PTFE composites. However, the transfer of the PTFE composites onto the surface of the GCr15 bearing steel can be greatly reduced by lubrication with liquid paraffin, but the transfer still takes place. Meanwhile, the interactions between the liquid paraffin and the PTFE composites, especially the absorption of liquid paraffin into the surface layers of the PTFE composites, create some cracks on the worn surfaces of the ceramic particle filled PTFE composites; the creation and development of these cracks reduces the load-supporting capacity of the PTFE composites. This leads to the deterioration of the friction and wear properties of the PTFE composites under higher loads in liquid paraffin lubrication. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2611–2619, 1999     

Structural,mechanical and tribological properties of Cu–ZrO2/GNPs hybrid nanocomposites

Hybrid Cu–ZrO₂/GNPs nanocomposites were successfully produced using powder metallurgy technique. The effect of GNPs mass fraction, 0, 0.5, 1 and 1.5%, on mechanical and tribological properties of the produced hybrid nanocomposite was studied while maintaining ZrO₂ mass fraction constant at 5%. High energy ball milling was applied for mixing powders and compaction and sintering were applied for consolidation. The morphological analysis of the produced powder showed acceleration of Cu particles fracture during ball milling with the addition of GNPs up to 0.5% with noticeable reduction of agglomeration size. Moreover, the crystallite size of Cu–5%ZrO₂/0.5%GNPs hybrid nanocomposites revealed smaller crystallite size, 142 nm, compared to 300 nm for Cu–5%ZrO₂ nanocomposite. Additionally, the hybrid nanocomposite with 0.5% GNPs shows homogeneous distribution of both reinforcement phases in the sintered samples. This improved nano and micro structure of Cu–5%ZrO₂/0.5%GNPs nanocomposites revealed higher hardness, 169.3 HV, compared to 65.5 HV for Cu–5%ZrO₂ nanocomposite. The wear rate is decreased in this composite while it increased with increasing GNPs content more than 0.5%. The coefficient of friction is decreased as well for this hybrid nanocomposite and remain constant with increasing GNPs content more than 0.5%.     

Enhanced mechanical and tribological properties of oscillatory pressure sintered WC–GNPs composites

It remains as a challenge to develop binderless WC ceramics that integrate high mechanical properties and low friction wear. Here, we report the preparation of strong and tough WC ceramics with low wear rate by adding graphene nanoplatelets (GNPs) and using oscillatory pressure sintering (OPS) process. The introduced GNPs lead to the formation of nearly fully dense composites with the aid of an oscillatory pressure. The OPS-prepared WC–0.3-wt% GNPs composites reached a high flexural strength, hardness, and fracture toughness, being up to 1420 MPa, 24.9 GPa, and 6.89 MPa m^1/2, respectively. Moreover, a low friction wear rate of 3.17 × 10⁻⁷ mm³ N⁻¹ m⁻¹ is achieved for such composites, which can be ascribed to the formation of a friction lubrication film during dry sliding friction process and their higher mechanical properties.     

ZrO2f-coated Cf hybrid fibrous reinforcements and properties of their reinforced ceramicizable phenolic resin matrix composites

Carbon fiber-reinforced ceramicizable phenolic resin matrix composites have been widely used in the field of thermal protection materials. In this paper, the ZrO_2f-coated C_f (ZrO_2f/C_f) hybrid fibrous reinforcements were designed to improve oxidation resistance of carbon fiber and ceramicizable composites reinforced by ZrO_2f/C_f hybrid fibrous reinforcements were prepared to investigated oxidation resistance and mechanical properties of the composites at high temperature. The results show that ZrO_2f/C_f hybrid fibrous reinforcements have good thermal stability and high oxidation resistance, and its ceramicizable composites have good bending strength at high temperature. Weight loss rate of the composites is only 21 %, and bending strength can be as high as 39 MPa when ablation time was 12 min at 1400 °C.     

Preparation,friction, wear,and fracture of the Si3N4-Ag-GNPs composites prepared by SPS

Silver and graphene nanoplatelets (Ag-GNPs) have been employed as reinforcements to prepare the self-lubricating silicon nitride matrix composites via 3D ball milling (Turbula) and spark plasma sintering. The prepared composites were characterized by scanning electron microscope with energy dispersive spectroscopy, Vickers hardness tester and reciprocating ball tribometer. Fracture surface morphology of the sintered composites indicated the potential reinforcement by the ductile silver phase. The mechanical property testing revealed that Si₃N₄ composites with Ag and GNPs incorporation exhibited lower hardness and slightly lower toughness compared with Si₃N₄ monolithic material. However, the coefficient of friction and wear in composites exhibited the lower values in 1 N friction force testing range.     

Effect of laser power on microstructure and tribological performance of WC−10Co4Cr coating

In order to enhance wear resistance of cold work molds, WC−10Co4Cr coating was fabricated on Cr12MoV steel by laser cladding. The morphologies, chemical compositions, and phases of obtained coatings were analyzed using a scanning electron microscopy (SEM), energy disperse spectroscopy, and X−ray diffraction, respectively. The effect of laser power on the tribological performance was analyzed using a ball−on−plate friction machine, and the wear mechanism was also discussed. The results show that the WC−10Co4Cr coating is composed of WC and Co₆W₆C phases, and the average hardness of coating cross−sections fabricated at the laser power of 1200, 1500, and 1800 W was 1296, 1375, and 1262 HV_0.5, respectively, in which that fabricated at the laser power of 1500 W is the highest among the three kinds of coatings. The average coefficients of friction of coatings fabricated at the laser power of 1200, 1500, and 1800 W are 0.61, 0.52, and 0.59, respectively; and the corresponding wear rates are 64.38, 35.38, and 123.92 μm³•N⁻¹•mm⁻¹, respectively, showing that the coating fabricated at the laser power of 1500 W has best friction reduction and wear resistance. The wear mechanism of WC−10Co4Cr coating is fatigue wear and abrasive wear, which is contributed to the increase of hard WC mass fraction.     

B4C reinforced NiTi-based composites: Microstructure and wear performance

In this study, NiTi–x wt.% B₄C (x = 0, 2, and 4) composites were consolidated with spark plasma sintering method, and the effects of boron carbide reinforcement addition on the microstructure and wear behavior of samples were investigated. Identification of the constituent phases of samples by the X-ray diffraction method plus Rietveld analysis revealed that the stability of the martensite phase increased in the composite samples because of mismatch stresses between the NiTi matrix phase and the reinforcing particles, which increases the density of the dislocations and facilitates the diffusion process that subsequently leads to the formation of stable intermetallics. The results of hardness test indicated that the hardness value increased from 3.67 GPa for pure NiTi to 10.99 GPa for NiTi–4 wt.% B₄C. Results of wear test revealed that boron carbide reinforced composite specimens had higher wear resistance, whereas wear rate of NiTi sample was 3.6 × 10⁻³ mm³/N m, and it reached to .21 × 10⁻³ mm³/N m for NiTi–4 wt.% B₄C. Investigation of microstructure by scanning electron microscopy images and EDS analysis revealed that the wear mechanism in NiTi samples was abrasive and the addition of B₄C to NiTi changed the wear mechanisms from abrasive to a combination of oxidation, adhesive, and delamination mechanisms.     

Investigations on mechanical behavior of hot rolled Al7075/TiO2/Gr hybrid composites

In the present work, influence of titanium dioxide (TiO₂) and graphite (Gr) hybrid reinforcement on microstructure and mechanical behavior of Al7075 alloy is studied. Al7075 and its hybrid composite samples were fabricated by using stir-casting and hot rolling technique. Hot rolling was carried out at a temperature of 450 °C with a reduction-ratio of 90%. Microstructure examination showed a good dispersion of titanium dioxide and graphite reinforcement particles with excellent bond with Al7075 matrix alloy. In case of hot rolling, both the reinforcements were found to be aligned in the direction of rolling. The microhardness and tensile strength of hybrid composites were remarkably improved in case of hot rolling compared to that of cast composites.     

Investigation of mechanical properties of Cu/Mo-SiCp composites produced with P/M,and their wear behaviour with the Taguchi method

In this study, metal matrix composite materials were produced by adding 0, 5, 10, and 15 wt% Mo and SiC_p powder particles into the Cu main matrix. Powder metallurgy processes were used as the production methods. These metal matrix composites were produced using a simple mixing method. Scanning electron microscopy was used to examine the surface morphology of the composites in different proportions. Density and hardness tests of the produced composite materials were performed. Taguchi's L₁₆ orthogonal array experimental design was used to describe the wear experiments. The parameters that affected the wear performance the most were determined. The highest relative density value was recorded as 89.18%. Significant increases in hardness (77.038 HRB) occurred in direct proportion to the increase of Mo and SiC_p powder particles. As a result of the wear tests, specific wear rate values of the obtained composite materials were determined. According to the optimised results, A₄B₃C₃D₂E₂F₂ (optimum) equation was obtained and the specific wear rate value was determined as 1.18642 × 10⁻⁷ mm³/Nm. Also it was found that the reinforcement ratios were relatively more effective compared to the other parameters.     

Effect of grain size and amount of zirconia on the physical and mechanical properties and the wear resistance of zirconia-toughened alumina

The effects of the ZrO₂ content and the particle size of ZrO₂ powders on the microstructure, phase composition, physical and mechanical properties, and the abrasion wear resistance of advanced Al₂O₃ ceramics and zirconia-toughened alumina (ZTA) composites containing 0 to 30 mass% yttria-stabilised zirconia (YSZ) were investigated. The composite with a ZTA content of 30 mass% of ZrO₂ exhibited the greatest resistance to abrasion wear. α-Al₂O₃ reflex broadening (hkl = 113) as a result of the microstresses in the Al₂O₃ crystal lattice during sandblasting decreased with increasing ZrO₂ amount, where the ZrO₂ particles located along the grain boundaries of Al₂O₃, hindering their growth and deformation. The use of nanodispersed ZrO₂ powder produced by the plasma chemical technique led to a 1.5-fold increase in wear resistance in the resultant ZTA ceramic.     

Microstructure and properties of Ni-WC gradient composite coating prepared by laser cladding

In this study, an Ni-based gradient composite coating reinforced with WC was prepared on a Q345R steel substrate by laser cladding. The Ni-WC composite coating was designed as a multilayer structure with gradient composition. The coating started with a layer of C276 alloy with 10 wt% WC on the substrate, and the subsequent layers were composed of Ni60 alloy with different WC contents (10, 30, and 50 wt% WC). The overall morphology, phase composition, and microstructure of the coatings were investigated. The microhardness and the wear properties of each layer of the coatings were also evaluated. The results showed that the gradient composition design was beneficial for reducing the cracking tendency. The coating was composed of an Ni-based matrix, WC, and multiple carbides and borides hard phases. With increasing WC content in the layers, the hard phases exhibited regional distribution characteristics. The WC reinforcement particles underwent different types of dissolution during the cladding process. From the surface to the substrate, the average microhardness of the coating was 1053.5 HV_0.2, 963.4 HV_0.2, 859.0 HV_0.2, 441.7 HV_0.2, and 260.5 HV_0.2. The wear tests revealed that the coefficient of friction and the wear loss values of the four layers were all lower than those of the substrate, demonstrating enhanced wear resistance.     

Influence of Cu-coated diamond addition on the microstructure and mechanical properties of WC-based cemented carbides

Cu-coated diamond enhanced tungsten carbide powder (WC)-Ni cemented carbides were successfully fabricated by spark plasma sintering method. Characterization of the phase composition and microstructure reveal that the diamond particles are well preserved and homogeneously distributed in the composites. Relative density of the samples improved from 92% to 97.6% with 2 wt% Cu-coated diamond addition. Vickers hardness and flexural strength of the samples achieved the maximum value of 2000 HV₁₀ and 950 MPa with 8 and 2 wt% addition, respectively. The fracture toughness improved from 8 to 11 MPa m^1/2 with the added content of diamond increasing from 0 to 4 wt%. The wear rate of the sample is reduced by five times with 6–8 wt% Cu-coated diamond addition. The wear mechanism mainly includes the removal of binder phase, the crushing of WC grains, and the crushing and pulling out of diamond particles.