Acoustic microscopy applied to ceramic pressure vessels and associated components

Alumina ceramic is being used extensively for external pressure vessels in naval applications. The material is also used in valves and other components, where reliability, immunity from corrosion, and high temperatures are required. This report presents a technique for the nondestructive evaluation of alumina ceramic components. The cracks were produced by CO₂ laser radiation. Since there is a need for the detection of very fine cracks, scanning acoustic microscopy was found to be superior to optical methods for imaging surface and subsurface cracks. We address the issue of crack initiation with the use of postirradiation analysis. This article reports our results on the evaluation of the surface and interior cracks with optical, scanning laser, scanning electron, and scanning acoustic microscopy. We present images of surface and subsurface microcracks generated at different power levels of a high power CO₂ laser system. The spatial variation of the Rayleigh wave velocity is measured by the V(z) curve technique. These preliminary data suggest that, with some improvement, the V(z) technique may detect residual stress with high spatial resolution.