A. H. Yegneswaran

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.

Abrasive wear of Al alloy-Al2O3 particle composite : a study on the combined effect of load and size of abrasive

Abstract The two-body abrasive wear behaviour of a cast aluminium alloy (ADC12) and ADC-12–10 wt.% Al2O3 particle composite was studied at different loads (1 N to 7 N) and abrasive sizes (30 μm to 80 μm). The wear behaviour was predicted through statistical analysis of the measured wear rate at different operating conditions. The wear rate (Y) is expressed in terms of the coded values of the abrasive size (x1) and applied load (x2) by the following linear regression equation: Y alloy =21.32+2.21x 1 +13.72x 2 +1.83x 2 (1) Y composite =17.32+3.17x 1 +14.84x 2 +2.86x 1 x 2 (2) where the multiplication factor is 10−11 m3/m. Eqs. 1 and 2 above suggests the following: (i) the effect of load on the wear rate of both the alloy and composite is more severe as compared to that of abrasive size, (ii) the effect of load and abrasive size on the wear rate is relatively more in case of composite material than that of the alloy and (iii) at certain combinations of load and abrasive size, the wear rate of composite may be higher as compared to that of alloy. The above factors (i), (ii) and (iii) were explained on the basis of operating wear mechanisms.

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.

Dry sliding wear characteristics of some zinc-aluminium alloys: a comparative study with a conventional bearing bronze at a slow speed

Abstract This study reports a few observations made regarding the dry sliding wear behaviour of a newly developed zinc-aluminium alloy. A conventionally used leaded-tin bronze and standard zinc-aluminium alloy have also been characterized under identical test conditions in order to assess the wear performance of the newly developed composition with respect to the conventional alloys and to understand the factors controlling the wear response. The study indicates that the bronze exhibited considerably inferior wear behaviour than the zinc-based alloys. In fact, the former revealed “chipping off” of material to such an extent that the specimens became quite small well before traversing the predetermined sliding distance at a specific pressure. As a result, no seizure pressure could be determined for the bronze. On the contrary, the zinc-based (standard as well as the modified) alloys showed considerably lower wear rates and better seizure characteristics than the bronze. The wear behaviour of the alloys has been explained on the basis of their microstructural features and further substantiated through the characteristics of the water surfaces, subsurface regions and debris particles generated during the tests. The analyses of the wear surfaces, subsurface regions and debris particles also enabled the operative wear mechanisms to be understood.

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.

Characterization of the wear response of a modified zinc-based alloy vis-à-vis a conventional zinc-based alloy and a bearing bronze at a high sliding speed

In this investigation, an attempt has been made to examine the wear response of a modified zinc-based alloy at a high speed (4.60 m/s) of sliding over a range of applied pressures. A conventional zinc-based alloy and a bearing bronze have also been subjected to identical tests with a view to assess the working capability of the modified alloy with respect to the existing ones. The wear characteristics of the alloys have been correlated with their microstructural features, while operating wear mechanisms have been studied through analyses of wear surfaces, subsurfaces, and debris particles. The conventional zinc-based alloy attained most inferior wear behavior when compared with that of the modified (zinc-based) alloy and the bronze. Interestingly, the modified alloy exhibited its wear response to be much better than that of the conventional zinc-based alloy due to the presence of nickel/silicon containing (hard and thermally stable) microconstituents. Moreover, the modified alloy also seized at a pressure similar to that of the bronze, although its wear rate prior to seizure was more than that of the latter. The study clearly indicates that it is possible to develop modified versions of zinc-based alloys having much improved wear characteristics over the conventional variety; the information gains special attention in view of the high speed of sliding selected in this study.

Factors controlling dry sliding wear behaviour of a leaded tin bronze

The sliding wear behaviour of a leaded tin bearing bronze was investigated over a range of applied pressures and sliding speeds with respect to the influence of microconstituents such as lead on the wear response. Significantly high wear rates were found at the minimum sliding speed due to extensive microcracking. This was evinced by the formation of coarse debris and considerable subsurface/wear surface cracking. The (micro) cracking tendency of the alloy prohibited the occurrence of subsurface deformation. The absence of a lead film was primarily due to the lead particles being engulfed in the coarse debris. Higher sliding speeds led to increased frictional heating making the alloy matrix viscoplastic. This in turn greatly suppressed the tendency of the alloy to exhibit microcracking, thereby facilitating interaction between the materials of the mating surfaces through wear induced plastic deformation. As a result, a stable transfer layer formed on the specimen surface. Interestingly, the formation of a...

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.

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.