O. P. Modi

Dry Sliding Wear Behaviour of Squeeze Cast Aluminium Alloy-Silicon Carbide Composites

Abstract Squeeze cast Al alloy (BSS: LM11) matrix composites, each containing 10 vol.% of SiC particles or fibres, have been investigated for their resistance to dry wear under varying applied pressures (1–3 MPa) at a sliding spped of 2.68 m s −1 against a rotating EN25 steel disc. Seizure pressure of the composites as well as the base alloy was determined using a pin-on-disc machine. The alloy containing SiC particles showed less wear rate than the one having SiC fibre dispersion. The base alloy showed maximum rate of wear. Dispersoid-matrix interfacial bonding and shape of the dispersoid were found to play an important role in governing the wear rate of the composites. Scanning electron microscopy examinations indicated relatively finer grooves on the wear surfaces prior to seizure, while seizure led to severely damaged surfaces. Similarly, wear debris generated during wear was thin and flaky prior to seizure, while bulky debris particles were observed during seizure. A few iron machining chips were also found in all the cases. The results obtained have been explained on the basis of wear-induced microstructural changes and deformation, leading to work hardening in the subsurface regions and wear debris.

Factors controlling the abrasive wear response of a zinc-based alloy silicon carbide particle composite

Abstract Attention has been focused in this study on the (two-body/high-stress) abrasion characteristics of a zinc-based alloy reinforced with hard SiC second phase articles (SPPs) under the influence of varying load, sliding distance and abrasive size. The unreinforced matrix alloy processed similarly was also subjected to identical test conditions. It was observed that the wear response of the specimens is influenced markedly by the applied load, sliding distance and the size of the abrasive particles. Different operative wear mechanisms were found to be responsible for the changing behaviour of the samples. Reinforcement with hard SPPs (SiC) in the zinc-based alloy matrix was beneficial when tests were conducted with fine abrasive particles over the entire range of applied loads and sliding distance. On the contrary, however, this trend reversed when coarser abrasive particles were used. Further, the wear rate reduced with sliding distance, while load affected the wear behaviour of the specimens in the opposite manner. These effects, of course, were more prominent under severe conditions of abrasion (i.e. higher load or coarser abrasive). The wear characteristics of the samples have been explained on the basis of factors such as degradation of the abrasive, as well as reinforcing SPP and abrasion-induced work hardening of the subsurface regions. In addition, the predominance of one or more processes such as capping, clogging, shelling and attrition, leading to a deteriorating cutting efficiency of the abrasive and brittle fragmentation of the SPPs, affected the wear response of the specimens markedly under a given set of experimental conditions.

Effect of interlamellar spacing on the mechanical properties of 0.65% C steel

The mechanical properties of a steel containing a nearly fully pearlitic structure have been examined as a function of the interlamellar spacing. The steel had been heat-treated at different austenitization temperatures in order to obtain varying interlamellar spacings. It was observed that hardness and yield strength follow a Hall–Petch type of relationship with respect to the interlamellar spacing but the ultimate tensile strength (UTS), percent elongation and impact toughness did not do so. It was noted that, below a critical size of interlamellar spacing, the UTS, impact toughness and ductility remained invariant to the interlamellar spacing. The results have been explained on the basis of a microstructure–thermal residual stress relationship.

Abrasive Wear behaviour of a high carbon steel: effects of microstructure and experimental parameters and correlation with mechanical properties

This investigation deals with the observations made towards understanding the role of interlamellar spacing on the high-stress abrasive wear behaviour of a high carbon steel. The samples revealed near-eutectoid (pearlitic) structure. The interlamellar spacing was varied by altering the austenitization temperature. Abrasion tests were conducted over a range of applied load, sliding speed, travel distance and abrasive size. Mechanical properties such as hardness, impact toughness and tensile strength, yield strength and elongation at fracture of the samples were also evaluated. The nature of dependence of abrasive wear rate and the measured mechanical properties on material related factors like interlamellar spacing of the samples has been analyzed. The study indicates that the wear rate does not follow a Hall-Petch relationship with the interlamellar spacing of the samples unlike hardness and yield strength. An analysis of the influence of abrasion test parameters suggested the wear rate to increase sharply with load initially. This was followed by a lower rate of increase or even a reduction in wear rate at higher loads depending on the interlamellar spacing of the samples. Increasing abrasive size caused the wear rate to practically remain unaffected initially. This was followed by a sharp increase in wear rate beyond a critical abrasive size. Increasing speed led to higher wear rates upto a critical sliding speed beyond which the wear rate decreased with a further increase in speed. The varying nature of influence of interlamellar spacing on mechanical properties and interlamellar spacing and abrasion test parameters on the wear response of the samples has been discussed in terms of wear-induced subsurface work hardening/deformation of the specimens, deteriorating cutting efficiency of the abrasive particles, stability of the deformed (transfer) layer in the near vicinity of the wear surface during abrasion and hardening of ferrite in the (eutectoid) cementite–ferrite (pearlite) mixture in the steel prior to testing.

Correlating microstructural features and mechanical properties with abrasion resistance of a high strength low alloy steel

A study towards the examination of the abrasive wear behaviour and other characteristics, viz. microstructure, tensile properties and hardness of a high strength low alloy steel has been carried out in order to establish a correlation amongst the parameters and to optimize the microstructural features and mechanical properties for superior wear performance. The steel was subjected to various heat treatment cycles for generating different combinations of microstructural features and mechanical and wear properties. The study suggests that, apart from hardness, ductility also plays a vital role in deciding the wear characteristics of steels. It has also been observed that an improvement in the abrasion resistance of the order of ∼50% can be achieved by subjecting the steel to suitable heat treatment cycles. Mechanical properties of the steel also change simultaneously. These features are ultimately controlled by the microstructural characteristics of the specimens. The results obtained have been supplemented through the characteristics of the worn surfaces, subsurface regions, debris and fractured surfaces. These analyses also helped to understand the operative mechanisms of material removal and failure.

The effect of different metallic counterface materials and different surface treatments on the wear and friction of polyamide 66 and its composite in rolling–sliding contact

Original article can be found at: http://www.sciencedirect.com/science/journal/00431648 Copyright Elsevier B. V. DOI: 10.1016/S0043-1648(03)00054-1

Corrosion behaviour of squeeze-cast aluminium alloy-silicon carbide composites

The corrosion behaviour of squeeze-cast Al alloy (LM11) separately dispersed with 10 vol% SiC fibres and SiC particles was investigated in 3% aqueous NaCl solution by general corrosion as well as potentiodynamic polarization techniques. Erosion-corrosion tests were also performed on the specimens in the solution. The base alloy was also subjected to identical tests to examine the influence of the presence of SiC in the matrix. The base alloy showed a lower corrosion rate than the composites. Furthermore, the alloy containing SiC fibres showed a higher corrosion rate than the one with SiC particle dispersion. Erosioncorrosion tests indicated that the rate of material loss followed a trend similar to that in other corrosion tests. The material loss was significantly higher in the case of erosion-corrosion tests. In addition to pitting and attack at the CuAl2 precipitate-Al interface in the matrix, dispersoid-matrix interfacial attack by the corrosion medium was also observed in the case of composites. On the other hand, erosion-corrosion revealed occasional partial removal of the dispersoid due to the impingement of the electrolyte. The tendency of the dispersoid removal by the impinging electrolyte was predominantly more in the case of the composites dispersed with SiC fibres. Results are explained in terms of the interfacial bonding as well as the shape of the dispersoid.

Two-body abrasion of a cast Al–Cu (2014 Al) alloy–Al2O3 particle composite: influence of heat treatment and abrasion test parameters

An Al–Cu (2014 Al) alloy reinforced with 10 vol.% Al2O3 particles (size: 75–150 μm), prepared by liquid metallurgy route, has been investigated under two-body (high stress) abrasive wear condition. The influence of varying load, abrasive size and sliding distance on the abrasive wear behaviour of the specimens was also studied. The base alloy prepared under similar condition has also been studied under identical test conditions in order to understand the influence of the dispersoid phase on the abrasive wear characteristics of the (base) alloy. In order to assess the role of matrix microstructure, the composite as well as the base alloy was subjected to abrasion in heat treated as well as in cast conditions. The results indicate that the Al2O3 particle reinforced cast Al alloy composite was more wear resistant (less wear rate) than the (unreinforced) matrix alloy when tested against 20, 35 and 60 μm size abrasive particles over the entire range of loads and sliding distances due to protection provided by the Al2O3 particles to the alloy matrix. On the other hand, a reverse trend was observed when 100 μm size abrasive particle was used as the abrasive medium above 1 N load due to greater microcracking tendency followed by fragmentation of dispersoid/abrasive particles. Unlike cast composite, heat treated composite exhibited better wear resistance (lesser wear rate) than the matrix alloy even when the tests were conducted against 100 μm size abrasive particles over the entire range of loads and sliding distances. Matrix strengthening and the morphological changes of the precipitate particles caused lower wear rate of the heat treated base alloy and composite over the cast ones. Abrasive wear rates were observed to decrease with sliding distance because of the increased extent of clogging, capping, shelling and attrition of the abrasive particles as well as subsurface hardening of the matrix. The wear behaviour of the specimens has been explained in terms of wear-induced subsurface work hardening, protection provided by the reinforced particles (in the case of composite) and degradation of the abrasive. Material removal mechanisms have also been studied through the examination of wear surfaces, subsurfaces, debris and abrasive particles.

Wear characteristics of a hardfaced steel in slurry

Abstract This study discusses some observations made during the wear testing of hardfaced layers deposited on a low carbon steel. Two kinds of (wear resistant) hardfacing materials were (separately) overlayed on a steel substrate and characterized for their microstructural features and wear behavior. Conditions of wear testing were varied in terms of the content of sand particles in the slurry, the speed of rotation of the specimens and the distance traversed. The substrate material was also subjected to identical tests in order to assess the effects of hardfacing/ overlaying. Hardfacing of the steel substrate resulted in a significant improvement in the wear resistance (inverse of wear rate) over that of the substrate, irrespective of the test conditions. Speed of rotation had a mixed influence on the wear rate wherein the intermediate speed caused maximum wear loss. The distance traversed had a mixed influence on the wear rate of the specimens in the sense that in some cases wear rate decreased with distance while a reverse trend was noted in the remaining situations, whereas under one test condition, the wear rate first decreased with distance, attained a minimum and then again tended to increase. Moreover, the larger sand content in the slurry led to lower wear rates. The wear behaviour of the specimens has been explained on the basis of the predominating material removal mechanisms, such as erosion and abrasion, in different situations. These have been further substantiated through their wear surface and sub-surface characteristics.

Abrasive wear behaviour of zinc-aluminium alloy - 10% Al2O3 composite through factorial design of experiment

AbstractTwo body abrasive wear behaviour of a zinc-aluminium alloy - 10% Al2O3 composite was studied at different loads (1–7 N) and abrasive sizes (20–275 μm) as a function of sliding distance and compared with the matrix alloy. The wear rate of the composite and the matrix alloy has been expressed in terms of the applied load, abrasive size and sliding distance using linear factorial design approach. The study suggests that the wear rate of the alloy and composite follow the following relations: