Minimizing tribolayer damage by strength-ductility matching in dual-scale structured Al-Sn alloys: A mechanism for improving wear performance

A mechanism for significant improvement of wear properties has been investigated. This operates by inducing a dual-scale structure consisting of coarse-grains (CG) and ultrafine-grains (UFG) in Al-12 wt%Sn alloys, in comparison with uniform UFG or CG structured alloys. It has been found that a dynamic steady tribolayer consisting of fine crystalline oxides plays a dominant role in improving the wear properties of both the UFG and dual-scale alloys. For the CG alloys, poor wear properties, caused by delamination wear of the tribolayer, could not be maintained on the worn surface. The tribolayer is formed on the worn surface by compacting and tribo-sintering of fine loose particles produced by sliding wear. However, the damage of the dynamic steady tribolayer is governed by the matching between ductility and strength of the matrix. The low ductility of the UFG alloy substrate causes the tribolayer to suffer crack damage rather easily, which limits any further improvement of its wear resistance. In contrast, for the CG alloys, the tribolayer is broken up and extruded into the matrix as a result of its low strength and a stable tribolayer could not be formed. The dual-scale structured alloy has excellent ductility-strength matching, and therefore a dynamic stable tribolayer can easily be maintained on the worn surface, leading to excellent wear performance.