High stress abrasive wear behaviour of aluminium hard particle composites: Effect of experimental parameters, particle size and volume fraction

High stress abrasive wear behaviour of aluminium alloy (ADC-12)–SiC particle reinforced composites has been studied as a function of applied load, reinforcement size and volume fraction, and has been compared with that of the matrix alloy. Two different size ranges (25–50 and 50–80 μm) of SiC particles have been used for synthesizing ADC-12–SiC composite. The volume fraction of SiC particles has been varied in the ranges from 5 to 15 wt%. It has been noted that the abrasive wear rate of the alloy reduced considerably due to addition of SiC particle and the wear rate of composite decreases linearly with increase in SiC content. It has also been noted that the wear resistance of composite varies inversely with square of the reinforcement size. The wear rate of the alloy and composite has been found to be a linear function of applied load but invariant to the abrasive size; at critical abrasive size, transition in wear behaviour is noted. This has been explained through analytically derived equations and wear–surface examination.     

The friction and wear of electroless Ni–P matrix with PTFE and/or SiC particles composite

In this paper, the friction behaviour and wear mechanism of electroless Ni–P matrix with PTFE and/or SiC particles composite coating are investigated by virtue of ring-on-disk wear machine at a high load of 150 N. The worn surface, wear debris and the composition changes after wear were characterized using scanning electron microscopy (SEM) and energy-dispersive analysis of X-ray (EDAX). By comparison with Ni–P and Ni–P–SiC coatings, the results indicated that the combination of a PTFE-rich mechanical mixed layer (PRMML) formed on the worn surface and hard SiC were responsible for the good tribological properties of the hybrid Ni–P–PTFE–SiC composites at high load. After heat treatment at 400 °C for 1 h, the wear rate of Ni–P matrix composites decreased with corresponding increase in microhardness. During sliding, an obvious decrease in the temperature rise with PTFE addition was attributed to the good anti-friction of PTFE.     

Tempering temperature effects on abrasive wear of mottled cast iron

The effects of different tempering temperatures (300–600 °C) on abrasive wear resistance of mottled cast iron were studied. Abrasive wear tests were carried out using the rubber-wheel test on quartz sand and the pin test on Al₂O₃ abrasive cloths. The retained austenite content of the matrix was determined by X-ray diffraction. The wear surface of the specimens was examined by scanning electron microscopy for identifying the wear micromechanism. Bulk hardness and matrix hardness before and after the tests were measured. The results showed that in the two-body (pin-on-disc test) system, the main wear mechanism was microcutting and high matrix hardening was presented. The wear rates presented higher correlation with the retained austenite than with the bulk and matrix hardness. In the three-body system (sand–rubber wheel), the wear surfaces presented indentations due to abrasive rolling. The wear rates had better correlation with both the bulk and matrix hardness (before and after the wear test) than with the retained austenite content. There are two groups of results, high and low wear rates corresponding to each tribosystem, two-body abrasive wear and three-body abrasive wear, respectively.     

Abrasive wear behaviour of laser sintered iron–SiC composites

Direct metal laser sintering (DMLS) is one of the popular rapid prototyping technologies for producing metal prototypes and tooling of complex geometry in a short time. However, processing of metal matrix composites (MMCs) by laser sintering is still in infant stage. Thermal cracks and de-bonding of reinforcements are reported while processing MMCs by laser sintering process. There are reports on use of metallic-coated ceramic reinforcements to overcome these problems. The present investigation is aimed at using nickel-coated SiC in developing iron composites by DMLS technique and to characterize its abrasive wear behaviour.Microstructure, microhardness, and abrasive wear tests have been carried out on both DMLS iron and its composites sintered at a laser scan speed of 100 mm/s. Abrasion wear tests have been carried out using a pin-on-disc type machine. SiC abrasive papers of grit size 60, 80, and 150 having an average particle size of 268, 192, and 93 μm, respectively, have been used. Load was varied between 5 and 25 N in steps of 5, while the sliding distance and sliding velocity of 540 m and 2.5 m/s, respectively was adopted for all the tests. Optical, scanning electron micrograph and surface roughness observation of worn surfaces have been undertaken.An increase in microhardness and a decrease in density of the laser sintered iron–SiC composites was observed with increase in SiC content. The abrasive wear resistance of composites increases with increased content of SiC in iron matrix. For a given grit size of SiC abrasive paper, at all the loads studied, iron–SiC composites exhibit excellent abrasive wear resistance. Increase in abrasive wear was observed with the increase in abrasive particle size.     

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.     

Cermets surface transformation under erosive and abrasive wear

The subsurface developed in ceramic-metal composites WC-Co, TiC-NiMo and Cr₃C₂-Ni during tribological testing (abrasion, sliding, erosion) under different conditions (impact angle, velocity, pressure, temperature) is the primary concern of the study. Mechanisms responsible for mechanically mixed layer (MML) development and wear resistance of materials are discussed in details. Instrumented indentation combined with consecutive polishing-testing procedure was used for mechanical characterisation. Microstructural features of the worn surface and subsurface region were studied with the help of optical microscope and scanning electron microscope equipped with energy dispersive spectroscopy analyser to evaluate difference between properties of the bulk and modified subsurface layers of materials.Formation of subsurface layer is found to be an essential feature of materials response to applied loading. Modified layer consists of highly deformed binder metal; cracked and decohesed large grains of carbides; embedded and/or fused debris of erosive/abrasive particles; and products of oxidation.     

Abrasive wear resistance of some commercial abrasion resistant steels evaluated by laboratory test methods

The aim of the present study is to evaluate the abrasive wear resistance of some potential abrasion resistant steels exposed to different types of abrasive wear contact conditions typical of mining and transportation applications. The steels investigated, include a ferritic stainless steel, a medium alloyed ferritic carbon steel and a medium alloyed martensitic carbon steel.The abrasive wear resistance of the steels was evaluated using two different laboratory test methods, i.e. pin-on-disc testing and paddle wear testing that expose the materials to sliding abrasion and impact abrasion, respectively. All tests were performed under dry conditions in air at room temperature. In order to evaluate the tribological response of the different steels post-test characterization of the worn surfaces were performed using optical surface profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. Besides, characterization of the wear induced sub-surface microstructure was performed using optical microscopy.The results show that depending on the abrasive conditions a combination of high hardness and toughness (fracture strain) is of importance in order to obtain a high wear resistance. In the pin-on-disc test (i.e. in sliding abrasion) these properties seem to be controlled by the as-rolled microstructure of the steels although a thin triboinduced sub-surface layer (5–10 μm in thickness) may influence the results. In contrast, in the paddle wear test (i.e. in impact abrasion), resulting in higher forces acting perpendicular to the surface by impacting stones, these properties are definitely controlled by the properties of the active sub-surface layer which also contains small imbedded stone fragments.     

Abrasive wear behaviour of bamboo

Abrasive wear of bamboo (Phyllostachys pubescens) against a free abrasive consisting of quartz sand (96.5%-wt) and bentonite (3.5%-wt) was studied on a rotary-disk type abrasive wear tester (a free abrasive wear tester) and the micromorphology of the abraded surfaces were examined by scanning electron microscopy. It was observed that the bamboo fibre (vascular bundle) orientation with respect to the abrading surface had an important influence on the abrasive wear performance. The normally oriented specimens gave much higher abrasion resistance than the parallel-oriented ones, the surface layer than the inner layer, and the vascular bundle than the matrix tissue.     

Dry wear and friction behaviour of plasma nitrided Ti–6AL–4 V alloy after explosive shock treatment

The unlubricated wear behaviour of explosive shock treated and, subsequently plasma nitrided Ti–6Al–4 V alloy was studied using a ball-on-disc wear tester. Plasma nitriding was carried out at three different temperatures (700, 800 and 900 °C) for 3, 6, 9 and 12 h. Plasma nitriding after explosive shock treatment enabled a reduction in the wear rate of two orders of magnitude. Detailed investigations of this improved wear performance dependent on the nitriding temperature and time were carried out. The friction and wear data showed a clear breakthrough transition from the nitrided layer to the core of the Ti–6Al–4 V alloy matrix. The lowest wear volume was obtained for the sample, nitrided at 900 °C for 12 h, especially at loads of 2.5, 5 and 7.5 N. Obviously, the hard nitride layers were intimately associated with low wear rate, providing a smooth low friction surface. The coefficient of friction reduced from 0.46 to 0.2 due to a thick and hard compound layer resulting from a high nitrogen diffusion rate caused by explosive shock treatment that expected to increase point defects in the alloy. Detailed examination of the wear tracks showed that plasma nitriding changes the mechanism of wear from one of adhesion for untreated Ti–6Al–4 V to both delamination and mild abrasive.     

硅晶片化学机械抛光材料去除机制与模型

通过分析软质层的形成、作用以及纳米磨料的自身变形对材料去除的影响，改进了CMP过程的接触力学模型；分析了纳米磨料自身变形量对磨料嵌入硅晶片基体材料的深度的影响，以及纳米磨料硬度对抛光表面粗糙度的影响。结果表明：软质层的存在增加了单个纳米磨料所去除材料的体积，且对基体材料有保护作用，减小了纳米磨料嵌入基体材料的深度；纳米磨料的自身变形抵消了纳米磨料嵌入基体材料的切削深度，从而也决定了抛光表面的粗糙度；纳米磨料的自身变形量与纳米磨料的硬度有关，硬度低的纳米磨料自身变形量大，因而切削深度小，抛光后表面的粗糙度值低。     

Wear behaviour of some low alloyed steels under combined impact/abrasion contact conditions

The wear behaviour of some low alloyed steels has been investigated using a laboratory impeller–tumbler wear test equipment in which the steel samples are worn by angular granite particles under combined impact/abrasion wear contact conditions. The wear of the steels was evaluated by weight loss of the steel samples while the wear mechanisms of the steels were investigated by post-test light optical microscopy (LOM), scanning electron microscopy and energy dispersive X-ray analysis. The worn steel surfaces display a very rough surface topography with pronounced craters and distinct grooves caused by high and low angle impacts, i.e. abrasive wear, respectively. Besides, fragments of embedded granite particles are frequently observed in the worn surface of the steels. The wear of the steels tends to decrease with increasing steel hardness. However, instead of using the bulk hardness value the hardness of the worn/plastically deformed surface layer should be used when modelling the wear resistance. Further, the wear resistance of the steels was found to be dependent on the microstructure and chemical composition. Steels with similar type of microstructure show a linear decrease in weight loss with decreasing grain size and increasing carbon content.     

Effect of surface nanocrystallization on abrasive wear properties in Hadfield steel

A nanocrystalline surface layer was synthesized on a Hadfield steel by shot peening treatment. The microstructure evolvement of the surface layer of the shot peening treated sample was characterized by optical microscopy, X-ray diffraction and high-resolution transmission electron microscopy. It has been shown that the grain sizes in surface layer were decreased to 11.1-17.4 nm after 60 min shot peening duration. Surface hardness was also increased greatly. Two- and three-body abrasive wear experiments were carried out for work hardening and original specimens, separately. The results showed that the wear resistance of the nanocrystallized Hadfield steel has distinctly been improved in case of soft particles used as two-body wear abrasives or light impact load applied for impact abrasive wear.     

Ball-cratering abrasion tests with large abrasive particles

The application of a ball-cratering method to test three-body abrasive wear of bulk materials in the presence of large abrasive particles has been investigated. Four types of abrasive particles of different sharpness were used to make slurries: glass beads, silica sand, crushed quartz and alumina. All the particles were sieved to a size of 250–300 μm. Two common industrial materials, mild steel and 27% Cr white cast iron, were used as wear samples. Wear rates of metallic samples were determined and the worn surfaces were examined by optical microscopy, SEM and Talysurf profilometry.It was found that the surface roughness of the ball significantly affects the wear rates and the wear mechanisms of the metallic samples. The surface roughness of the ball steadily increased with testing time and was mainly affected by the angularity of abrasive particles. More angular particles generated higher ball surface roughness. It was found that the gradual increase in the ball surface roughness was responsible for non-linearity of wear rates with sliding time. The increasing depth of the wear craters also contributed to this non-linearity as deeper craters facilitate particle entrainment. Three-body rolling wear dominated when the ball was smooth and the contribution of two-body grooving wear increased with increasing the ball roughness. Softer mild steel samples were more affected by the ball roughness changes than the harder white cast iron samples. Wear surface morphology was also affected by the angularity of particles and by the material properties of wear samples. Particle fracture was found in all four groups of abrasives and the angularity of the particles was slightly altered. Therefore, the ball-cratering test, under the testing conditions used, can be considered as a high-stress abrasion test.     

High resolution observations of friction-induced oxide and its interaction with the worn surface

A detailed transmission electron microscopy study of oxide and oxygen-containing phase formation during the sliding wear of metals, composites and coatings is provided. A wide range of different materials types are reported in order to compare and contrast their oxidational wear behaviour: a low carbon stainless steel, a H21 tool steel containing 7%TiC particles, a 17%Cr white iron, an Al–Si/30%SiC composite, an Al–alloy (6092)–15%Ni₃Al composite and finally a 3rd generation TiAlN/CrN ‘superhard’ multilayer coating. For the ferrous alloys, nanoscale oxides and oxygen-containing phases were formed that exhibited excellent adhesion to the substrate. In all cases, an increase in oxide coverage of the surface was associated with a decrease in Lancaster wear coefficient. The oxide at the surface of the 316L and H21+7%TiC was found to deform with the substrate, forming a mechanically mixed layer that enhanced surface wear resistance. Evidence of oxidational wear is presented for the wear of the Al–Si–30%SiC composite, but this did not give a beneficial effect in wear, a result of the brittle nature of the oxide that resulted in detachment of fine (150nm) thick fragments. The worn surface of the Al–alloy (6092)–15%Ni₃Al and TiAlN/CrN coating was characterized by reaction with the counterface and subsequent oxidation, the product of which enhanced wear resistance. The observations are related to the classical theory of oxidational wear.     

Studies on friction and transfer layer using inclined scratch

Friction influences the nature of transfer layer formed at the interface between die and sheet during forming. In the present investigation, basic studies were conducted using ‘Inclined Scratch Test’ to understand the mechanism of transfer layer formation during sliding of pins made of an Al–Mg alloy on EN8 steel flats of different surface roughness under dry and lubricated conditions. The surfaces produced can be categorized into three different types: (a) uni-directional (b) 8-ground and (c) random. Rubbing the EN8 flat in a uni-directional manner and a criss-cross manner on emery sheets produced the uni-directional and 8 ground surfaces. The random surfaces were produced by polishing the EN8 flats using various abrasive powders. The influence of the ‘nature of surface roughness’ on material transfer and coefficient of friction were investigated. Scanning Electron Microscopy studies were performed on the contact surfaces of the Al–Mg alloy pins and EN8 steel flats to reveal the morphology of the transfer layer obtained. It was seen that the transfer layer is dependant on the coefficient of friction. The coefficient of friction, which has two components—the adhesion component and the plowing component, is controlled by the ‘nature of surface’. A surface that promotes plane strain conditions near the surfaces increases the plowing component of friction.     

Micro-scale abrasive wear testing of duplex and non-duplex (single-layered) PVD (Ti,Al)N, TiN and Cr–N coatings

A micro-scale abrasive wear test, based on ball-cratering, has been used to evaluate the wear resistance of duplex and non-duplex (Ti,Al)N, TiN and Cr–N coatings. The term duplex is used here when plasma nitriding is followed by PVD coating. Coatings without the plasma nitriding stage are termed single-layered. Coating properties were evaluated by surface profilometry, hardness and scratch testing. All duplex coatings showed higher micro-abrasive wear resistance than their single-layered counterparts, with the duplex (Ti,Al)N coating achieving the best performance. After a certain number of ball revolutions, the coating material became worn through, exposing the substrate material. After this point, the presence of a hard nitrided case diminished the scratching action of the SiC abrasive particles. The experimental results also indicate that the choice of the PVD coating plays an important role in improving the micro-abrasive wear resistance. Apart from single-layered and duplex Cr–N coatings, all the other coating systems provided a higher micro-abrasive wear resistance than the uncoated substrate (hardened AISI H13 steel). The poor abrasive wear resistance recorded for the single-layered and duplex Cr–N coatings could be attributed to the hardness of the Cr–N being much lower than that of the SiC abrasive particles, which caused tearing of the coating with subsequent delamination. The wear pattern observed was found to change from surfaces characterised by grooves (uncoated substrate, single-layered TiN and Cr–N systems and duplex Cr–N system) to surfaces which exhibited multiply indented surfaces (single-layered and duplex (Ti,Al)N systems), indicating a transition between wear mechanisms. This transition was found to be dependent on the ratio between the hardness of the SiC abrasive particles and surface (coating) or subsurface hardness. By decreasing this ratio, the ability of the SiC abrasive particles to scratch the composite surface was reduced and the resistance to micro-scale abrasion was improved.     

Tribological properties of flame sprayed Fe–Ni–RE alloy coatings under reciprocating sliding

Fe–Ni–RE self-fluxing alloy powders were flame sprayed onto 1045 carbon steel. The tribological properties of Fe–Ni–RE alloy coatings under dry sliding against SAE52100 steel at ambient conditions were studied on an Optimol SRV oscillating friction and wear tester in a ball-on-disc contact configuration. Effects of load and sliding speed on tribological properties of the Fe–Ni–RE coatings were investigated. The worn surfaces of the Fe–Ni–RE alloy coatings were examined with a scanning electron microscopy(SEM) and an energy-dispersive spectroscopy(EDS). It was found that the Fe–Ni–RE alloy coatings had better wear resistance than the SAE52100 steel. An adhered oxide debris layer was formed on the worn surface in friction. Area of the friction layer varied with variety of sliding speed, but did not vary with load. The oxide layer contributed to decreased wear, but increased friction. Wear rate of the material increased with the load, but dramatically decreased at first and then slightly decreased the sliding speed. The friction coefficient of the material was 0.40-0.58, and decreased slightly with the load, but increased with sliding speed at first, and then tended to be a constant value. Wear mechanism of the coatings was oxidation wear and a large amount of counterpart material was transferred to the coatings.     

Tribology at high-velocity impact

The tribological events taking place when a high-velocity projectile hits a SiC particulate reinforced AA 5083 composite material was examined under real conditions. The samples were cast in a disc shape by squeeze casting method. Different volume fractions of SiC particles were used. They were solidified under 180 MPa in a steel mould with a 650–700 °C temperature range. SiC particles with the size of 250–500 μm, and 30% and 45% in volume fraction were incorporated into the matrix material. The composites were machined to ensure a smooth surface and to obtain samples without burrs. The samples had a diameter and thickness of 140 and 20 mm, respectively. The terminal ballistic tests were carried out in an army zone under standard test conditions. An AP 7.62 mm armour piercing projectile with a speed of 710 m/s was used for testing the composite.The frictional characteristics and wear mechanisms caused by high-velocity impacts to the composite were determined by SE microscopy studies. The evaluations of the tribological events on both the hole and projectile tip surfaces resulting from high-velocity friction were carried on. As the projectile moved thorough the composite, some material broke from the matrix body and conglomerated along the path followed by the missile. Then these conglomerated blocks yielded and slided along the hole surface. There were also scratching and local melting on the hole surface. Similarly, some ploughing took place on the hole, some SiC particles were removed from the matrix body by the friction effect of projectile and these particles were conglomareted on the tip surface of the projectile. Thus, the nature of wear mechanism on the projectile surface was predominantly abrasive while those of the friction surfaces of the composites were predominantly abrasion and melt wear.     

Effect of Aramid Pulp and Lapinas Fiber on the Friction and Wear Behavior of NBR Powder–Modified Phenolic Resin Composite

Short fiber reinforcement plays a definite role in governing the performance of a composite through the improvement of different material properties. The present investigation deals with the effect of aramid pulp and lapinas fiber on the friction and wear characteristics of a composite made from phenolic resin modified by powdered acrylonitrile butadiene rubber (NBR) on a pin-on-disc tribometer. Four composites, containing 10, 20, 30, and 40 wt% of aramid pulp with respect to phenolic resin content, were prepared. Another four composites, containing 50, 100, 200, and 300 wt% of lapinas fiber with respect to phenolic resin content, were also made. It was found that the two different fibers have distinctly different contributions to the friction and wear properties of the composites. It was also found that the incorporation of aramid pulp enhances friction stability of the composites much better than that of lapinas fiber. The change in surface morphology of these composites was studied by scanning electron microscopy (SEM) before and after the friction test. SEM images of friction samples containing aramid pulp corroborated the occurrence of wear through an adhesive wear mechanism, whereas the lapinas fiber–containing composites showed an abrasive wear mechanism.