Focused Ion Beam Studies of Worn Surfaces

Focused ion beam (FIB) microscopy has been available for over 20 years, but substantial improvements in recent years has delivered a powerful technique for the study of surface structures. Ion channeling contrast, produced by secondary electron emission from the Ga ion interaction with the surface is a high sensitivity, high resolution technique for revealing phase distributions and deformed structures. Moreover, the ion beam can be used to take sections of the worn surface for subsequently removal for TEM. Despite the major advantages of ion channeling contrast and 3-D sectioning, the technique has only recently been applied to worn surfaces. This paper demonstrates the power of the technique in the study of the worn surface of 3 very different materials, namely 1) Al-alloy metal matrix composites, reinforced with MoSi₂ and CrSi₃, worn under lubricated sliding, with very low wear rates; 2) hot rolled aluminium alloys, where the surface structure leads to enhanced Filiform corrosion, and finally 3) the worn surface of TiAlN/VN multilayer coatings, where friction induced oxide formation results in significant changes in friction coefficient.