Applications of scanning acoustic microscopy in analyzing wear and single-point abrasion damage

Abstract

Wear science has historically relied heavily on observations of surface features to elucidate the fundamental nature of wear processes. A host of surface imaging techniques are currently available, each with its own set of strengths and limitations. This paper considers the application of scanning acoustic microscopy (SAM) for analysis of wear damage processes. Reflection-mode SAM images are produced by the interaction of focused, high-frequency (100 MHz-2 GHz) sound waves with solid surfaces, and contrast is produced by localized variations in near-surface elastic properties. A powerful advantage of SAM is its ability to probe subsurface regions where fractures and delaminations may be concealed from the view of traditional light-optical and electron-optical instruments. The current paper will describe the principles of SAM and illustrate several of its uses in wear surface analysis; specifically, as regards the imaging of elastic strain fields near single-point abrasion damage in silicon carbide, in elucidating the geometry of slip line fields produced during friction tests of an oriented single crystal of stainless steel, and in studying the highly deformed layers of a taper-sectioned intermetallic alloy of Ni 3Al. SAM images are compared with photomicrographs of the same worn areas to illustrate the strengths and limitations inherent in the technique.