Effect of SiC Particle Size on Wear Properties of Al2O3·SiO2/SiC/Mg Hybrid Metal Matrix Composites

The aim of this study was to investigate the effect of SiC particle size on the wear properties of magnesium-based hybrid metal matrix composites (MMCs) reinforced with Saffil short fibers and SiC particles. Hybrid MMCs with different SiC particle sizes of 1, 7, and 20 μm, respectively, were fabricated by the squeeze infiltration process. The volume fractions of Saffil short fibers and SiC particles in the hybrid composites were 15 and 5%, respectively. Wear tests were carried out using a ball-on-disk against a steel ball under the dry sliding condition. The test results showed that the composite with large-sized SiC particles had an improved wear resistance compared with the smaller sized particles.     

Dry sliding wear behaviour of Al(Mg)/Al2O3 interpenetrating composites produced by a pressureless infiltration technique

Aluminium alloys, reinforced with ceramic particles or fibres, are desired materials in high performance applications due to their superior properties. In this paper, gel-cast Al₂O₃ foams were pressurelessly infiltrated using an Al–8 wt.% Mg alloy. The wear rates of the alloy and the Al(Mg)/Al₂O₃ interpenetrating composites were tested under dry sliding conditions; effects of Al₂O₃ foam density and cell size on the composite wear resistance under different loads and sliding distances were investigated. A ‘ploughing’ mechanism was observed in all the composites after an initial 250 m sliding distance, whilst the composites with the higher foam density show a ‘two-stage’ wear with sliding distance. The decrease in the wear rate in the second stage in the latter is attributed to an Al₂O₃ network protruding out of the worn surface, which protects the direct wear of the Al(Mg) alloy by the counter ball. Within the range studied, a larger cell size is preferred for better wear resistance.     

Influence of particle content and porosity on the wear behaviour of cast in situ Al(Mn)–Al2O3(MnO2) composite

Aluminium-based tribological materials may reduce the weight of components, leading to significant fuel economy. The aim of the present study is to investigate the wear and friction in cast in situ Al(Mn)–Al₂O₃(MnO₂) composites synthesized by dispersing MnO₂ particles in molten aluminium, which get reduced to form Al₂O₃ particles. Wear tests have been conducted at four normal loads of 9.8, 19.6, 29.4 and 39.2 N and at a constant sliding speed of 1.05 m/s using a pin-on-disc wear testing machine, under dry sliding conditions. The results of the investigation indicate that the cumulative volume loss and wear rate of in situ composites are significantly lower than those observed in either the commercial aluminium or Al–Mn base alloy, under similar loading and sliding conditions. The influences of both reinforcing particle and porosity contents on the tribological behaviour of in situ composites were evaluated. It has been found that at a given particle content, the wear rate increases with increasing porosity content due to its combined effect on real area of contact and subsurface cracking. The wear rate of in situ composites with relatively lower porosity decreases with increasing particle content, but does not appear to change significantly or even increases a little with increasing particle content when the composites have relatively higher porosity. In view of large fluctuations in coefficient of friction during sliding, no effect of particle or porosity contents on the coefficient of friction could be determined unambiguously for different in situ composites.     

Wear behaviour of Al/(Al2O3p+SiCp) hybrid composites

In this study, dry sliding metal–metal and metal–abrasive wear behaviours of the aluminium matrix hybrid composites produced by pressure infiltration technique were investigated. These composites were reinforced with 37 vol% Al₂O₃ and 25 vol% SiC particles and contained up to 8 wt% Mg in their matrixes. While matrix hardness and compression strength increased, amount of porosity and impact toughness decreased with increasing Mg content of the matrix. Metal–metal and metal–abrasive wear tests revealed that wear resistance of the composites increased with increasing Mg addition. On the other hand, abrasive resistance decreased with increasing test temperature, especially above 200 °C.     

Wear behavior of SiC particulate reinforced aluminum composites sliding against steel balls under dry and lubricated conditions

Wear behavior of Al–Si alloys reinforced with SiC particulate has been investigated under dry and lubricated reciprocating sliding conditions using a ball-on-block wear test method. It was shown that in the dry sliding wear of the composite/steel ball system, the wear mechanism of the composite was predominantly adhesive. With further sliding motion, delamination and abrasive wear occurred as a result of fracture and debonding of the SiC particles. Under lubricated conditions, the wear rate of the composite was drastically reduced due to the presence of the lubricant, and a boundary lubrication condition existed and dominated the normal wear process. The debonding of the SiC particles from the matrix of the composite was a predominant factor in determining the wear loss of the composite in the boundary lubrication sliding process. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tribological behavior and wear mechanisms of MoSi2-base composites sliding against AA6063 alloy at elevated temperature

Intermetallic Mo(Si,Al)₂, Mo(Si,Al)₂/Al₂O₃, Mo(Si,Al)₂/SiC and Mo(Si,Al)₂/ZrO₂ composites produced by spark plasma sintering of mechanically alloyed powders were tested on a block-on-cylinder apparatus, sliding against an AA6063 alloy cylinder at elevated temperature. Abrasion, micro-fracture and surface tribochemical reactions were found to be the operative wear mechanisms, producing severe wear in the investigated alloys. Abrasive wear by pull-out of Al₂O₃ and micro-fracture of Mo(Si,Al)₂ particles promotes severe wear in the Mo(Si,Al)₂/Al₂O₃ composite. In the Mo(Si,Al)₂/SiC composites, hard SiC inclusions suppressed the abrasive wear, but a tribochemical reaction was found to be the dominant wear mechanism. A combination of abrasion by pull-out of Al₂O₃ particles and a tribochemical reaction was revealed to be the main wear mechanism in the Mo(Si,Al)₂/ZrO₂ materials. The brittleness index B = H/K_1C was applicable for prediction of the relative wear resistance. In agreement with the suggested model, the lowest wear rate, corresponding to B = 5.5–6.5 μm^−1/2, was found in the Mo(Si,Al)₂/30 vol.% SiC and Mo(Si,Al)₂/30 vol.% ZrO₂ composites.     

Tribological behaviour of SiC?TiC?TiB2 composites under unlubricated sliding conditions

The friction and wear behaviour of eight different SiC TiC TiB₂ composite materials, with a practically constant SiC:TiC ratio of 1 and an increasing amount of TiB₂, was determined comparatively in oscillating sliding tests at room temperature under unlubricated conditions. The influence of the relative humidity (RH) of the surrounding air was investigated in tests in dry, normal, and moist air. All tests were performed against SiC balls and Al₂O₃ balls as counterbodies. The friction was affected by RH but barely at all by the composition of the composites. The wear resistance of the composites was found to be improved considerably by addition of TiB₂ in the range 20–60%. The highest wear resistance of the system was found when Al₂O₃ was used as the counterbody material.     

Dry sliding wear mechanism for P/M austenitic stainless steels and their composites containing Al2O3 and Y2O3 particles

Austenitic stainless steels are used in applications demanding general corrosion resistance at room or moderate operating temperatures. However, their use is often limited by the relative softness of these materials and their suceptibility to wear and galling. The present investigation deals with the dry sliding wear behaviour of two P/M austenitic stainless steels (AISI 304L and 316L) and their composites containing two different ceramic particles (Al₂O₃ and Y₂O₃) and two different sintering activators (BN and B₂Cr). Unlubricated pin-on-disc wear tests were carried out. Wear mechanisms were analysed by means of scanning electron microscopy and X-ray diffraction. A plastic deformation and particle detachment wear mechanism was revealed. Plasticity during sliding induced an austenite to martensite transformation. The presence of ceramic particles (Al₂O₃ and Y₂O₃) and sintering activators (B₂Cr, BN) improved significantly the wear resistance (especially the combination Al₂O₃ and B₂Cr). Ceramic particles limited plastic deformation while sintering activators decreased final porosity.     

Tribological Properties of Organic Functionalized ZrB<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Epoxy Composites

The tribological behaviors of epoxy composites filled with organic functionalized ZrB₂–Al₂O₃ were environmentally investigated and compared with those with as-received fillers under both dry and oil sliding conditions in this work. The worn surfaces and the transfer films on the counterparts were characterized by scanning electronic microscope (SEM), and the frictional temperature rising was investigated by infrared thermometer. The results demonstrated that the coefficient of friction (CoF), the wear rate, as well as the frictional temperature rise of the epoxy composites were all decreased due to the introduction of ZrB₂–Al₂O₃ fillers. And with the increase in filler content, similar variation tendencies of CoF and wear rate of epoxy composites were observed under the different sliding conditions. Besides, the organic functionalization of ZrB₂–Al₂O₃ fillers, which made the epoxy composites exhibit lower CoF and wear rate than those with as-received fillers, lowered the frictional temperature as well. In comparison, the epoxy composites filled with 5 vol% modified fillers presented better tribological properties, suggesting a stronger interfacial bonding between modified fillers and epoxy matrix. The dominant wear mechanisms of filled composites under dry and oil sliding conditions could be inferred as the combination of adhesive wear and abrasive wear and the fatigue wear, respectively, on the basis of SEM images of worn surfaces.     

Sliding Wear of an Al Alloy SiC Whisker Composite

The tribological properties of a well-studied powder metallurgy metal-matrix composite, i.e., 20 volume percent SiC whiskers in 2124-T6 Al alloy matrix, were measured for the three principal orthogonal orientations under dry and lubricated sliding contacts. The sliding wear mechanisms were identified through analyses of wear tracks and subsurface microstructure by scanning and transmission electron microscopy techniques. The results for sliding wear of this 2124 Al-SiC whisker composite indicate a much higher wear when dry than when lubricated, and a strong wear anistropy, which is correlated with the ureal fraction of SiC whiskers on the wear plane. SEM and TEM analyses show direct evidence of adhesive wear through plastic deformation for dry sliding and abrasive wear through plowing and polishing for lubricated sliding.     

Effect of Al2O3 Particle Size on Electrical Wear Performance of Al2O3/Cu Composites

Al₂O₃/Cu composites (1.0 vol%) reinforced with different size of α-Al₂O₃ particles were fabricated by a powder metallurgy method and electrical sliding wear tests were performed on a self-made pin-on-disk electrical wear tester. The effect of Al₂O₃ particle size on electrical wear performance of the Al₂O₃/Cu composite was studied, and the wear mechanism of the Al₂O₃/Cu composite was also discussed based on worn surface observations. The results show that the tribological properties of A1₂O₃/Cu composite are closely related to the mechanical properties. With an increase in Al₂O₃ particle size, the wear rates of A1₂O₃/Cu composites have a reverse variation with hardness of A1₂O₃/Cu composites. In the range of 50–100 nm, Al₂O₃/Cu composites have the highest wear resistance and mechanical properties. Microstructural observation revealed that the wear mechanisms of Al₂O₃/Cu composites were mainly adhesive wear and plastic deformation accompanied by a small amount of arc damage. In addition, the plastic deformation area on the pin sample of the frictional end depends on the electrical wear resistance of A1₂O₃/Cu composites.     

Wear mechanisms of K2Ti4O9 whiskers reinforced Al20Si aluminum matrix composites with lubrication of water and tetradecane

The tribological properties of K₂Ti₄O₉ whisker reinforced Al20Si aluminum matrix composites were investigated in a mode of low amplitude reciprocal sliding. The ball-on-disk tests were performed at applied loads of 20–100 N and sliding velocity of 0.09 m s⁻¹. The water lubricated composites demonstrated higher wear resistance and friction coefficient than the tetradecane lubricated composites did. The main wear mechanism is microgrooving at low applied loads and tribochemical wear at high applied loads for the pairs lubricated with water, microgrooving at all test loads for the pairs lubricated with tetradecane.     

A study on friction and wear characteristics of nanometer Al2O3 /PEEK composites under the dry sliding condition

The friction and wear properties of the polyetheretherketone (PEEK) based composites filled with 5 mass% nanometer or micron Al₂O₃ with or without 10 mass% polytetrafluroethylene (PTFE) against the medium carbon steel (AISI 1045 steel) ring under the dry sliding condition at Amsler wear tester were examined. A constant sliding velocity of 0.42 m s⁻¹ and a load of 196 N were used in all experiments. The average diameter 250 μm PEEK powders, the 15 or 90 nm Al₂O₃ nano-particles or 500 nm Al₂O₃ particles and/or the PTFE fine powders of diameter 50 μm were mechanically mixed in alcohol, and then the block composite specimens were prepared by the heat compression moulding. The homogeneously dispersion of the Al₂O₃ nano-particles in PEEK matrix of the prepared composites was analyzed by the atomic force microscopy (AFM). The wear testing results showed that nanometer and micron Al₂O₃ reduced the wear coefficient of PEEK composites without PTFE effectively, but not reduced the friction coefficient. The filling of 10 mass% PTFE into pure PEEK resulted in a decrease of the friction coefficient and the wear coefficient of the filled composite simultaneously. However, when 10 mass% PTFE was filled into Al₂O₃/ PEEK composites, the friction coefficient was decreased and the wear coefficient increased. The worn scars on the tested composite specimen surfaces and steel ring surfaces were observed by scanning electron microscopy (SEM). A thin, uniform, and tenacious transferred film on the surface of the steel rings against the PEEK composites filled with 5 mass% 15 nm Al₂O₃ particles but without PTFE was formed. The components of the transferred films were detected by energy dispersive spectrometry (EDS). The results indicated that the nanometer Al₂O₃ as the filler, together with PEEK matrix, transferred to the counterpart ring surface during the sliding friction and wear. Therefore, the ability of Al₂O₃ to improve the wear resistant behaviors is closely related to the ability to improve the characteristics of the transfer film.     

Effect of the Graphite Content on the Tribological Behavior of Al/Gr and Al/30SiC/Gr Composites Processed by In Situ Powder Metallurgy (IPM) Method

The influence of graphite content on the dry sliding wear characteristics of Al6061/Gr composites along with Al6061/30SiC/Gr hybrid composites has been assessed using a pin-on-disc wear test. The composites with different volume fraction of graphite particles up to 13% were processed by in situ powder metallurgy (IPM) technique. The porosity and hardness of the resultant composites were also examined. It was found that an increase in the graphite content reduced the porosity, hardness, and friction coefficient of both types of composites. The hybrid composites were more porous and exhibited higher hardness and lower coefficient of friction at identical graphite contents. The increased graphite content in the range of 0–13 vol.% resulted in increased wear rate of Al/Gr composites. The Al/30SiC composite exhibited a lower wear rate as compared with the base alloy and graphite addition up to 9 vol.% improved the wear resistance of these hybrid composites. However, more graphite particles addition resulted in increased wear rate. SEM micrographs revealed that the wear mechanism was changed from mostly adhesive in the base alloy sample (Al/0Gr) to the prominently abrasive and delamination wear for Al/Gr and Al/SiC/Gr/composites.     

Friction and Wear Properties of 3D Carbon/Silicon Carbide Composites Prepared by Liquid Silicon Infiltration

Carbon/silicon carbide (C/SiC) composites were prepared by a liquid silicon infiltration (LSI) process and their microstructure and friction and wear properties studied. The matrices of the C/C green bodies were found to be reinforced with dense carbon fiber bundles hanging together. The density of the composites before and after the LSI process was 1.25 and 1.94 g/cm³, respectively. However, the open porosity of C/SiC composites was about 16% due to the opening of closed pores during the machining process. The C/SiC composites exhibited excellent tribological properties in the dry condition, with an average coefficient of friction (COF) and wear rate of about 0.29 and 16.15 μg/m MPa, respectively. In comparison, the average COF was about 0.13 in the moist condition, with a wear rate of 5.87 μg/m MPa. The main wear mechanism of the C/SiC composites was worn particles and debris with a high degree of hardness, producing a plough effect on the friction surface in the dry condition and an adhesive effect in the moist condition.     

Wear behaviour of in situ Cu–Al2O3 composites produced by internal oxidation of as cast alloys

Abstract

In the present study, the wear behaviour of Cu–Al₂O₃ composites and Cu–Al alloys has been investigated. The experiment involved casting of Cu–Al alloys with 0·37, 1, 2 and 3 wt-% of aluminium under inert gas atmosphere. The composites were produced by internal oxidation of alloys at 950°C for 10 h in presence of Fe₂O₃ and Al₂O₃ powders mixture. The microstructures of composites were studied using SEM and atomic force microscopy. To identify wear behaviour of specimens, dry sliding pin-on-disk wear tests were conducted according to ASTM G99-95a standard. The normal loads of 20, 30, and 40 N were applied on specimens during wear tests. The sliding speed and distances were selected as 0·5 m s^–1 and 500, 1000 and 1500 m respectively. To specify the wear mechanisms, the worn surfaces of composites were examined by SEM equipped with EDX. According to wear test results, increasing applied load and sliding distance leads to more volume loss in all specimens. Composites represent better wear resistance in comparison to alloys. Additionally, increasing the volume fraction of alumina particles in composites enhances the wear resistance, especially under high applied load. The wear mechanisms are mainly abrasion, oxidation and delamination.     

Tribological characteristics of polycrystalline Magnéli-type titanium dioxides

The results presented in this paper have clarified experimentally, that titania-based Magnéli-phases (Ti₄O₇/Ti₅O₉ and Ti₆O₁₁) with (121)-shear planes exhibit more anti-wear properties than lubricious (low-frictional) properties. The results for dry sliding indicate that the coefficients of friction lie in the range of 0.1–0.6 depending on sliding speed and ambient temperature. The COF decreased with increasing temperature (T= 22–800°C) and increasing sliding speed (υ= 1−6 m/s). The dry sliding wear rate was lowest for the Al₂O₃ at 1 m/s at 800°C with values of 1.7 × 10−8 and 6.4 × 10−8 mm³/N m, comparable to boundary/mixed lubrication, associated with a high dry frictional power loss of 30 W/mm². The running-in wear length and, more important, the wear rate decreased under oscillating sliding tests with increasing relative humidity. The contact pressure for high-/low-wear transition increased under oscillating sliding tests with increasing relative humidity. At room temperature and a relative humidity of 100% the steady-state wear rate under dry oscillating sliding for the couple Al₂O₃/Ti₄O₇–Ti₅O₉ was lower than 2 × 10−7 mm³/N m and therefore inferior to the resolution of the continuous wear measurement sensor. TEM of wear tracks from oscillating sliding revealed at room temperature a work-hardening as mechanism to explain the running-in behavior and the high wear resistance. The hydroxylation of titania surfaces favours the high-/low-wear transition. This revised version was published online in August 2006 with corrections to the Cover Date.     

The influence of alumina on mechanical and tribological characteristics of graphite particle reinforced hybrid Al-MMC

We consider the influence of alumina (Al₂O₃) particles on mechanical and tribological properties of aluminum hybrid metal matrix composites (MMC). Various weight fraction of Al₂O₃ (5, 10 and 15%) and constant weight fraction of graphite (5%) were used to fabricate composites by stir casting method. The effect of Al₂O₃ content on hardness, density and specific wear rate is evaluated. A wear test was performed using central composite design matrix on a pin-on disc apparatus at room temperature for constant sliding distance of 1000 m. The sliding speed, load and weight fraction of Al₂O₃ were the process variables. The results show that the hardness and density increase with increase in Al₂O₃ content. From the analysis of variance (ANOVA), load is the dominant factor that affects the specific wear rate of hybrid composites followed by speed and weight fraction of Al₂O₃. Based on desirability approach, the improvement in the wear resistance of the composites became more prominent at high speed, high load and high weight fraction of Al₂O₃. The worn surface of the pin was examined using scanning electron microscope (SEM) which indicates that the wear mechanism of composites is mostly abrasive wear followed by oxide wear.     

Effect of the Thermal Expansion Characteristics of Reinforcements on the Electrical Wear Performance of Copper Matrix Composite

Copper matrix composites reinforced with MgO, Al₂O₃, SiO₂, and SiC nanoparticles were fabricated by powder metallurgy. The tribological properties of the composites were examined using a self-made pin-on-disk electrical wear tester. Thermal expansion properties of the prepared composites were evaluated by their coefficient of thermal expansion from 50 to 500°C. The effect of the thermal expansion characteristics of reinforcements on the electrical wear performance of the composites was also studied. The results showed that the wear rates of MgO/Cu and Al₂O₃/Cu composites were lower than those of SiC/Cu and SiO₂/Cu composites, which were also consistent with the difference between the coefficient of thermal expansion of the copper matrix and reinforcements. The relationship was analyzed by calculation of the thermal stress at the copper matrix–reinforcement interface in the electrical sliding process. Microstructural observation revealed that the wear mechanisms of the copper matrix composites were mainly adhesive wear and plastic deformation accompanied by a small amount of arc damage.