Factors controlling dry sliding wear behaviour of a leaded tin bronze

Abstract

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 lead film on the wear surface was also observed under these conditions. The above factors were mainly responsible for the improved wear behaviour of the alloy at higher speeds. Finer debris formation, less surface and subsurface damage, and the presence of both a deformed and stable transfer layer and a lead film strongly supported these observations. Material removal mechanisms involved delamination of the undeformed subsurface region causing chipping off at the minimum sliding speed. Higher speeds, however, caused delamination of the transfer layer. In addition to adhesion, three body abrasion was found to contribute considerably towards material removal. The formation and stability of a transfer layer and the presence of a lead film are at least two major factors which control the wear behaviour of leaded tin bronzes. It is found that the above phenomena which provide improved wear characteristics occur only under specific sliding conditions.

MST/3218