The Effect of Heat Treatment on Sliding Wear Behaviour of a Zinc-Based Alloy Containing Nickel and Silicon

Abstract

This investigation deals with the observations made pertaining to the sliding wear behaviour of a zinc-based alloy containing nickel and silicon in partially lubricated condition. Wear tests were conducted over a range of applied pressures and sliding speeds. The effect of microstructural changes brought about through T6 heat treatment involving solutionizing followed by artificial ageing on wear behaviour was also investigated. The wear rate increased with pressure. The slope of the wear rate versus pressure plots was low initially up to a specific pressure. This was followed by a higher slope beyond the (specific) pressure. In some cases, the rate of change in wear rate, i.e. the slope, decreased at still higher pressures. Moreover, the (specific) pressure decreased with sliding speed in general. Increasing sliding speed caused the wear rate of the as-cast zinc-based alloy to increase up to a sliding speed of 2.68 m/s. The trend reversed at a still higher speed of 4.60 m/s. However, increasing wear rate with speed was noted for the heat-treated alloy over the entire speed range. Heat treatment led to reduced wear rate up to a sliding speed of 2.68 m/s. An opposite trend was observed at a higher speed of 4.60 m/s in this case. Specimen seizure was noted at speeds above 2.68 m/s in the case of the as-cast alloy whereas seizure took place only at 4.60 m/s for the heat-treated alloy samples. Frictional heating increased with pressure and speed. The specific response and changing mode of distribution of various phases were thought to be responsible for the typical wear behaviour of the alloy in specific material and test conditions. The predominance of parameters like thermal stability and cracking tendency over each other is suggested to lead to the varying wear behaviour of the alloy in different (material and sliding) conditions. The wear response of the samples has been substantiated through characteristics of their wear surfaces, subsurface regions and debris.