B. K. Prasad

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.

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.

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.

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.

Effect of microstructure on the sliding wear performance of a Zn–Al–Ni alloy

Abstract Some observations pertaining to the sliding wear characteristics of a zinc–aluminium alloy containing nickel under varying material and test conditions have been reported in this investigation. Dry sliding wear tests were conducted on as-cast and heat-treated zinc-based alloy pins using a pin-on-disc machine. A steel disc was employed as the counterface. Sliding speeds adopted were 0.42, 2.68 and 4.60 m/s while the traversal distance was fixed at 500 m. Wear tests were conducted at different pressures using separate pins in each case. Seizure pressure of the pins (prior to traversing the sliding distance of 500 m) was determined at each speed. Wear rate and the extent of frictional heating increased with pressure and speed whereas seizure pressure practically followed a reverse trend. The wear rate versus pressure plot of the as-cast alloy pins assumed two slopes at the lowest speed wherein low slope (indicating the occurrence of mild wear situation) was noticed initially. This was followed by the attainment of a higher slope suggesting severe wear condition at increased pressures. At higher speeds, one slope only (identical to the higher slope at the minimum speed) was noted. Wear rate versus pressure plots of the heat-treated alloy pins followed a trend similar to the as-cast ones except that two slopes were noted up to the intermediate speed in the former case. Heat treatment changed the as-cast dendritic structure of the zinc-based alloy into the one with an improved uniformity of the distribution of various microconstituents, the nickel containing phase remaining practically unaffected. Softening of the (as-cast) alloy was also observed as a result of the heat treatment. However, in spite of reduced hardness, the heat-treated alloy pins attained improved wear behaviour (i.e. reduced frictional heating and low wear rate) over the as-cast ones irrespective of the test conditions. This was attributed to a more uniform distribution of microconstituents and reduced cracking tendency of the alloy as a result of the heat treatment. The alloy pins also attained better seizure pressure in heat-treated condition comparing with the as-cast ones at all the speeds except the maximum for the same reasons. A reversal in the trend at the maximum speed was thought to be due to the over-softening of the already softened (heat-treated) alloy pins under the influence of large frictional heat generated at the (maximum) speed. Under the circumstances, the heat-treated alloy pins tended to adhere/fuse with the disc extensively while this tendency was relatively less for the as-cast ones in view of their higher hardness. Further, the extent of the negative influence of cracking tendency reduced allowing thermal stability to predominate the wear behaviour of the as-cast alloy pins in this case. The factor led to somewhat higher seizure pressure of the (as-cast) alloy pins at the maximum speed comparing with the heat-treated ones. Low wear rates correlated with less damage to the worn surfaces and to the regions below the worn surfaces and finer debris formation. Seizure led to severe damage to the worn surfaces and to the regions below the worn surfaces while the debris formed was quite bulky and coarser.

Abrasion-induced microstructural changes and material removal mechanisms in squeeze-cast aluminium alloy-silicon carbide composites

An attempt has been made to understand wear-induced subsurface microstructural changes and material removal mechanisms in squeeze-cast BS LM11 alloy dispersed with 10 vol% SiC. Particles as well as fibres of SiC were separately dispersed in the alloy matrix to determine the influence of shape of the dispersoid on the abrasion behaviour of the latter. Abrasion tests were conducted on a standard rubber wheel abrasion test apparatus. Silica sand was used as the abrasive medium. Abrasive wear rates of the specimens were found to decrease gradually with the number of test intervals until a steady state value was attained. This was attributed to the protrusion of the reinforcement phase and abrasion-induced work hardening of the matrix in regions close to the abraded surface. The dispersoid/matrix interface as well as the shape of the dispersoid was found to influence the abrasion rate of the composites. A poor dispersoid/matrix interface led to higher rate of abrasion due to pull-out of the dispersoid. On the other hand, good bonding between the dispersoid and the matrix helped the dispersoid phase to be retained by the matrix, offering reduced rate of abrasion.

Plant Fiber — Industrial Waste Reinforced Polymer Composites as a Potential Wood Substitute Material

This investigation deals with the property characterization and utilization of abundantly available and renewable resources of plant fibers such as jute and sisal. These plant fibers along with industrial wastes (fly ash and red mud) have been used for synthesizing value added composite materials. Relevant engineering properties such as physical and mechanical, resistance to abrasive wear, weathering and fire, etc., of the plant fiber reinforced polymer matrix composites so synthesized were characterized. The characteristics of conventional wood and other commercially available potential candidate building materials were also compared to assess the application potential of the newly developed materials vis-a-vis their conventional counterparts. The study reveals that the developed polymer—natural fiber—industrial (inorganic) waste composites attain far superior mechanical properties and resistance to abrasive wear, fire, water absorption, weathering, and chemical attack, as compared to their conventional counterparts such as wood, medium density fibre (MDF) boards, particle board, etc. The versatile material system so developed has potential for wood substitute applications like door shutters, flooring tiles, roofing sheets, partitions, etc., and is envisaged to significantly contribute towards forest conservation and environmental protection. The study strongly suggests that the newly developed plant fiber and/or industrial waste reinforced polymer composite materials are quite capable to serve as a potential cost and energy effective, technologically viable, and attractive substitute to the conventionally used wood and other identical materials. The study gains significance from the fact that earlier investigators have focussed their attention mainly towards exploring the use of chopped (sisal), and textile (jute) composites for different engineering applications including building while the present study examines the suitability of abundantly available natural fibers such as sisal and jute in the presence of otherwise harmful industrial wastes like red mud and fly ash for synthesizing polymer-based composites. This is followed by assessing the potential of the developed composite materials as a cost and energy effective wood substitute for building applications.

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...