Margam Chandrasekaran

Effect of particle-porosity clusters on tribological behavior of cast aluminum alloy A356-SiCp metal matrix composites

Aluminum alloy composites have evoked keen interest in recent times for potential applications in aerospace and automotive industries owing to their superior strength-to-weight ratio and high-temperature strength. In the automotive industry, these materials have been evaluated for applications such as pistons, piston ring inserts, cylinder liners, brake rotors, brake pads and connecting rods. However, the extensive use of such composites is still largely unrealized due to the limited knowledge of the processing-microstructure-property relationship in such materials. In this work, cast A356-SiCp metal matrix composites with up to 15 vol.% reinforcement were produced by the melt stirring technique. The composites thus produced were evaluated for their microstructural and tribological properties. The uniformity of distribution of SiC particles (SiCp) was found to improve with increasing SiC content. Porosity was found to increase with increase in SiCp content incorporated. However, the extent of particle-porosity interaction (clustering) was observed to be greater for low SiC content composites as compared to higher SiC content composites. In sliding contact against an AISI 1060 steel counterface, it was observed that the interaction between the load on the composite specimen and the extent of particle-porosity clustering in the specimen played a significant role in determining the wear and friction behavior of the composite. For composites showing greater extent of clustering, an increase in the pressure×sliding velocity (PV) from low (0.25 MPa m s−1) to intermediate (0.5 MPa m s−1) values caused an increase in wear, while a further increase in PV value (to 0.75 MPa m s−1) caused a reduction in wear. On the other hand, composites, which showed lesser tendency to form particle-porosity clusters, exhibited very little change in the wear even with increasing PV values. The difference in wear behavior between the unreinforced alloy and between the various composite specimens has been attributed to the interactive effect between the particle-porosity clusters and the PV value under which wear takes place. A qualitative model, explaining the interaction between the particle-porosity clusters and the wear conditions (PV value) and its concomitant influence on wear of the material, has been proposed.

Friction surfacing of metal coatings on steel and aluminum substrate

Friction surfacing of (i) tool steel, inconel, aluminum and titanium rods onto mild steel substrates and (ii) stainless steel, mild steel and inconel onto aluminum substrates was investigated. It was found that tool steel and inconel were efficiently deposited onto steel to form a dense strong coating while aluminum was only deposited at high contact pressures. Titanium could not be deposited under the tested conditions. Stainless steel, mild steel and inconel could be deposited onto aluminum substrates to form dense coatings, however only SS displayed a lack of intermetallic compound formation with Al. Melting of Al by frictional heat was observed and this led to the formation of brittle and therefore undesirable intermetallic compounds at the interface of the coating. X-ray microscope investigations of the coatings confirmed that the structure of the coating is a continuous series of discrete layers inclined at a shallow angle to the phase of the substrate. Fissures were found between these layers close to the outer surface of the coating, which implies that the uppermost layers should be removed to obtain the best quality of coating. Microscopic observations revealed that there was little mixing between the coating and the steel substrate but some surface roughening and sub-surface deformation of the steel substrate by friction surfacing. The Al-alloy substrate showed similar types of surface alteration but to a far greater extent. Careful control of process parameters such as substrate, speed, load and consumable was necessary for coating quality.

Materials degradation and its control by surface engineering

Mechanisms of Materials Degradation: Mechanical Causes of Materials Degradation Chemical Causes of Materials Degradation Materials Degradation Induced by Heat and Other Forms of Energy Duplex Causes of Materials Degradation Surface Engineering: Discrete Coatings Integral Coatings and Modified Surface Layers Characterization of Surface Coatings Application of Control Techniques: Control of Materials Degradation Financial and Industrial Aspects of Materials Degradation and Its Control.

In situ observation of sliding wear tests of butyl rubber in the presence of lubricants in an X-ray microfocus instrument

Abstract The friction and wear of butyl rubber sliding on a hard abrasive in unidirectional sliding was investigated as a function of temperature and load. Experiments were conducted in an X-ray microscope chamber using apin on disk apparatus. Dry tests and tests under lubricated conditions with water and oil at room and elevated temperatures were performed. The experiments indicated that the presence of a lubricant such as water or oil reduced the coefficient of friction but caused accelerated wear due to chemical deterioration of rubber. Observation under the X-ray microscope of rubber sliding also indicated propagation of Schallamach waves in rubber during sliding and non-uniform contact between the rubber and the abrasive paper.

Tribology of UHMWPE tested against a stainless steel counterface in unidirectional sliding in presence of model synovial fluids : part 1

Friction and wear tests have been performed on ultra-high molecular weight polyethylene (UHMWPE) in presence of proteins, dry sliding conditions against a steel counterface disc and the results have been analyzed in detail. UHMWPE was found to exhibit lowest friction coefficient and wear rates when lubricated with bovine α globulin and with bovine albumin respectively. Post-test analysis of the proteins indicated denaturing, formation of reaction products of specimens and proteins. The predominant wear mechanisms found were adhesion, abrasion and fatigue.

Study of the interfacial phenomena during friction surfacing of mild steel with tool steel and inconel

Friction surfacing was carried out with tool steel (AISI 01) and inconel 600 consumables on mild steel 1020 substrate in an argon atmosphere. Inconel bonded strongly with the substrate and there was evidence of interfacial compound formation between the substrate and coating. For tool steel coatings, a sharp boundary between the substrate and coating was observed by scanning electron microscopy. X-ray fluoroscopic imaging also revealed this boundary. Mechanical interlocking between the coating and the substrate appears to be insignificant so adhesion between the coatings and the substrate may be caused by solid-phase bonding. For friction surfacing of both tool steel and inconel, a nominal contact pressure as high as 21.8 MPa was required to obtain an adherent coating of uniform quality.

Study of the interfacial phenomena during friction surfacing of aluminium with steels

Friction surfacing was carried out with stainless steel 304 and mild steel 1020 consumables on to an aluminium 5083 substrate in an argon atmosphere. Mild steel bonded well with the substrate and there was evidence of interfacial compound formation whereas in the case of stainless steel consumable there was no evidence of mixing and the coating was found to have a rolled structure on the surface. No clear evidence of mechanical interlock was obtained for stainless steel on aluminium. In both cases a nominal contact pressure as high as 21.8 MPa was required to obtain a good coating. For the mild steel coating there was evidence of transfer of aluminium on to the coating and the matrix had a shear crack along the matrix/coating interface.

Service Characteristics Of Biomedical Materials And Implants

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Effect of counterface on the tribology of UHMWPE in the presence of proteins

Artificial joints in orthopedics occupy a principal position owing to the increase in number of cases suffering from arthritis and associated diseases in addition to impairment caused by accidents. In this work, one of the most commonly used joint material, i.e. ultrahigh molecular weight polyethylene (UHMWPE), was tested against the duplex stainless steels instead of the conventional 316 L stainless steel. The UHMWPE was found to exhibit the lowest friction coefficient and wear rates when lubricated with water followed by globulin and glucose. The friction coefficient in the presence of egg albumen was higher along with high wear rates recorded. Post-test evaluation of surface roughness and wear scar/track analysis was performed to identify the wear mechanisms. Worn surfaces were analyzed using a differential scanning calorimeter for changes in crystallinity with sliding. The specimens tested under lubricated conditions with glucose, egg albumen and globulin indicated the presence of reaction products on the worn surface. Adhesive and corrosive wear mechanisms were the predominant modes of wear identified on the polymer samples. The wear tracks indicated that the proteins did react with the counterface material forming a thin deposit on them. Low temperature nitriding of the duplex stainless steel counterfaces were performed and the UHMWPE specimens were tested under similar conditions against the nitrided surfaces. Low temperature nitriding of the counterface did result in improved tribological behavior of UHMWPE and the corrosive effects were minimal.

Sintered iron–copper–tin–lead antifriction materials — effect of temperature

Abstract Fe–4.5 wt.% Cu–1.75 wt.% Sn–1 wt.% MoS 2 antifriction material with varying additions of Pb (0.0–12.5 wt.%) were developed by a conventional powder metallurgy route by sintering at 800, 850 and 900°C for 20–50 min and the mechanical and frictional properties of the sintered compacts were evaluated. Addition of Pb up to 7.5 wt.% improved the antifrictional and mechanical properties, whereas further addition deteriorated these properties. The lowest coefficient of friction of 0.08 at the PV value of 0.76 MPa ms −1 and the maximum hardness level of 254 VHN were obtained for the composition containing 7.5 wt.% Pb sintered at 850°C for 30 min.