ABSTRACT
Wear is not an intrinsic material property. Wear is a complex function of the system which includes material properties, operating conditions (load, speed), contact geometry, surface roughness, and environment (lubrication, temperature). Therefore, for a given pair of material combination, wear can vary over several orders of magnitude depending on the conditions. This makes evaluation of materials in terms of wear resistance difficult. Common practice is to conduct simulation wear tests to rank materials under the same operating conditions. If the relationship between wear and the operating conditions (load and speed) are linear, relative ranking of materials will hold. Under the influence of chemistry or environment, unfortunately, wear transitions often occur and the relationship between wear and the operating conditions is often not linear. The relative ranking of materials, therefore, will change when the operating conditions are changed. At the same time, material variations abound. Small changes in the alloying elements and processing conditions change the wear characteristics. So even though the material designation is the same, there is no assurance that the chemical composition and microstructure are identical. Because of these factors, literature reports on material wear characteristics have wide ranges, as shown for ceramics in Table 9.1. For metals, similar ranges are observed for data from all sources. The metal wear data in Table 9.1 show the effect of lubricants on different metals on a single wear tester in a laboratory (Fein, 1975). This makes selection of materials for wear applications difficult.
