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.     

Sliding wear behaviour of Zinc–Nickel alloy electrodeposits

The sliding wear behaviour of zinc–nickel electrodeposited coatings on mild steel substrates was investigated using a spherical pin-on-disc apparatus. The pin materials were alumina and hardened steel. The composition of the coatings was the following: 86 wt% zinc–14 wt% nickel. The friction coefficient of zinc–nickel coating against alumina counter spheres was found to be higher than that against hardened steel counter spheres. The weight loss of zinc–nickel coating after sliding against hardened steel counter spheres was found to be lower than that against alumina counter spheres. The main wear mechanism of the zinc–nickel coating sliding against stainless steel was noted to be severe shearing of the surface layers of the coating due to the ploughing action of the steel pins. For the wear experiments of zinc–nickel coatings against alumina spheres, a surface delamination mechanism is proposed to be the predominant wear mechanism of the coatings.     

Sliding metallic wear test with in-process wear measurement: A new approach to collecting and applying wear data

A wear test is described in which the edge of a hard wedge is loaded against the periphery of a rotating disc of softer specimen material. The applied normal load is kept approximately constant during a test. As the test progresses and the disc diameter is reduced by the wear taking place the wedge moves radially inward. By measuring this inward movement during a test it is shown how the wear can be continually monitored. Results are given and it is shown how these might be applied in practice, taking into account the influence of both surface roughness and lubrication.     

Wear and friction behavior of sand cast brake rotor made of A359-20 vol% SiC particle composites sliding against automobile friction material

The effect of load range of 30-100 N and speed range of 3-12 m/s on the wear and friction behavior of sand cast brake rotor made of A359-20 vol% SiC particle composites sliding against automobile friction material was investigated. Dry sliding frictional and wear behavior were investigated in a pin-on-disc type apparatus. Automobile friction material was used as pin, while the A359-20 vol% SiC particle composites formed the rotating disc. For comparison, the wear and friction behavior of commercially used cast iron brake rotor were studied. The results showed that the wear rate of the composite disc decreased with increasing the applied load from 30 to 50 N and increased with increasing the load from 50 to100 N. However, the wear rate of the composite disc decreased with increasing the sliding speed at all levels of load applied in the present work. For all sliding speeds, the friction coefficient of the composite disc decreased with applied load. The worn surfaces as well as wear debris were studied using scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analyzer and X-ray diffraction (XRD) technique. At load of 50 N and speed range of 3-12 m/s, the worn surface of the composite disc showed a dark adherent layer, which mostly consisted of constituents of the friction material. This layer acted as a protective coating and lubricant, resulting in an improvement in the wear resistance of the composite.     

Sliding wear behaviour of Ca α-sialon ceramics at 600 °C in air

As an extension of a previous investigation on the wear behaviour of Ca α-sialon ceramics of differing microstructures at room temperature, wear testing was conducted at 600 °C in air to explore the effects of microstructure, contact pressure and sliding speed on the wear behaviour. Under all loading conditions from 1 MPa to 1 GPa, a constant high friction coefficient was observed and a severe wear process was dominant, in which the sliding contact induced cracks were observed in different microstructures. Wear particles were generated along the wear track, but no tribofilm was detected. Increasing the sliding speed from 10 to 23 cm/s was found to significantly increase wear rate. However, variations in microstructure had little impact. That is, large elongated-grained α-sialon exhibited only a slightly lower wear rate than fine equiaxed-grained α-sialon.     

Role of zirconium diboride particles on microstructure and wear behaviour of AA7075 in situ aluminium matrix composites at elevated temperature

ABSTRACT

The present research work examines the impact of temperature on the dry sliding wear behaviour of AA7075 aluminium strengthened zirconium diboride (ZrB₂) particulate composite (0, 3, 6, 9 and 12?wt.%). The dry sliding wear behaviour of the AMCs was inspected utilizing a pin-on-disc machine at differing temperatures (40, 60, 120, 180 and 240°C). The wear resistance of AMCs improved with the increased substance of ZrB₂ particulates at all test temperatures. The worn surface of the AMC pins was described utilizing FESEM. It was found from the SEM micrographs of worn surface, that at different temperatures, adhesion and metal flow were the prime wear process of the AA7075 composites, while for in situ formed AMCs, metal stream and oxidation were the factors affecting the wear process. The worn surface of the AMCs showed that there was a modification in wear component from abrasive wear to metal flow.     

Dry sliding wear behaviour of an aluminium alloy–granite particle composite

In the present study, the effect of granite reinforcement on the dry sliding wear behaviour of an aluminium–silicon alloy (BS:LM6) was investigated using a pin-on-disc machine. The composite was prepared using liquid metallurgy technique wherein 10 wt.% granite particles were incorporated in the matrix alloy. Sliding wear tests were conducted at applied loads in the range 0.2–1.6 MPa and speeds of 1.89, 3.96 and 5.55 m/s. The matrix alloy was also prepared and tested under identical conditions in order to see the influence of the dispersoid phase on wear behaviour. It was observed that the composite exhibited lower wear rate than that of the matrix alloy. Increasing applied load increased the wear rate. In the case of the composite, the wear rate decreased with speed except at higher pressures at the maximum speed; the trend reversed in the latter case. On the contrary, the matrix alloy exhibited minimum wear rate at the intermediate test speed. Seizure pressure of the composite was significantly higher than that of the matrix alloy, while temperature rise near the contacting surfaces and the coefficient of friction followed an opposite trend. SEM examination of the worn surfaces, subsurface regions and debris enabled to understand the operating wear mechanisms.     

Dry wear and friction properties of an A356/SiC foam interpenetrating phase composite

The dry sliding wear and friction behaviors of A356 aluminum alloy and a hybrid composite of A356 aluminum alloy and silicon carbide foam in the form of an interpenetrating phase composite were evaluated using a ball-on-disk apparatus at ambient conditions. The stationary 6.35 mm alumina ball produced a wear track (scar) diameter of 7 mm on the rotating specimen surface. Three different loads; 5 N, 10 N and 20 N were applied at a constant sliding speed of 33 mm/s for both materials. Wear tracks were characterized with a scanning electron microscope and measured with an optical surface profilometer. In general, this novel A356/SiC foam composite reduced the friction coefficient and wear rate from that of the base alloy for all loading conditions. In addition, as the load increased, the friction coefficient and wear rate decreased for both materials. The results indicate the composite could be used in light-weight applications where moderate strength and wear properties are needed.     

Erosive-corrosive wear of aluminum alloy composites: Influence of slurry composition and speed

The Erosion-corrosion behavior of a SiC particle reinforced Al-Si alloy has been studied in two different environments, namely saline and acidic, to simulate sea water and mining atmospheres, respectively. These studies were performed at different sand concentrations (20-40 wt%) and varying rotational speeds (700-900 rpm). It is noted from the present study that the composite exhibited better wear resistance than the alloy in marine and acidic atmospheres irrespective of sand content and speed. It is also noted that the wear rates increased with increasing sand content and speed irrespective of material due to increase in the severity of erosive/abrasive attacks. However, the wear rates decreased at higher speeds (e.g., 1100 rpm) due to increased intercollisions and rebounding and also the decrease in the mobility of the erodant particles. It is observed that erosion is the dominant mode of material removal in these two media. Corrosive attack was more predominant in the acidic media than in the NaCl media at lower sand concentrations (0-20 wt%). However, at higher sand concentrations (30-40 wt%) corrosive attack was more severe in the NaCl medium. Scanning electron microscopic (SEM) observation shows that Al/Si interfaces act as predominant sites for corrosion attack rather than the Al/SiC interfaces. Formation and removal of the passive layer, preferential attack at the Al/Si interfaces, fragmentation and wear of SiC particles were observed as mechanisms of material removal in marine and acidic media. SEM studies of the eroded-corroded surfaces indicated that an increase in the sand content of the slurry and in the rotational speed of the slurry increased resulted in greater damage to the SiC particles and matrix, resulting in an increase in wear rates.     

A comparison of the relative friction and wear responses of PTFE and a PTFE-based composite when tested using three different types of sliding wear machines

In this work, the tribological behavior of a commercially available polytetrafluoroethylene-based composite material filled with polyimide microparticles has been thoroughly investigated using different approaches. Specifically, two standard tribological tests, i.e., pin-on-disc and thrust washer measurements, have been compared with sliding tests performed on real components using a specially designed lab bench. The obtained results demonstrated that, despite the different testing methods (continuous rotation vs. reciprocating linear movement for the pin-on-disc/thrust washer and sliding tests, respectively), the different techniques provide highly comparable data within the adopted experimental conditions and can be successfully combined to assess the overall tribological features of this PTFE-based polymer composite.     

Effect of Wettability Enhancement of SiC Particles on Impact Toughness and Dry Sliding Wear Behavior of Compocasted A356/20SiCp Composites

In this study, the effect of wettability improvement of SiCp on the impact and sliding wear behavior of A356/20 wt% SiCp composites produced by a compocasting technique has been investigated. The result showed an increase of incorporation and uniform distribution of SiCp in the A356 matrix by elimination of SiCp segregation. Desired bonding between SiCp and the aluminum matrix due to improved wettability resulted in enhanced properties in terms of improved impact toughness and wear resistance. This improvement was also associated with partial refinement of coarse eutectic silicon due to increased incorporation and distribution of SiCp reinforcements. The highest enhancement was obtained when 1% Mg was added into the melt in addition to pretreated SiCp. The impact toughness value increased by 10 and 26% and the wear rate decreased by 5 and 30% when the SiC was treated and when Mg was added, respectively, compared to as-received SiCp. The impact fracture surfaces showed fewer decohered and well-bonded SiC particles in A356–(SiC-treated-Mg) composite. The highest wear resistance of A356/SiCp composites was achieved by A356–(SiC-treated-Mg) composite for applied loads of 10 and 20 N compared to other fabricated composites. The worn surface revealed mild abrasion and adhesion wear mechanisms.