Ultrasound—Linear and Nonlinear—as a Probe of Microstructural Change in Metals and Alloys

Ultrasound has long been used to non-destructively test for materials flaws as a prevention against brittle fracture. Could it be similarly used to test for precursors to ductile failure? Two of the key players in the plastic deformation attendant to ductile failure of metals and alloys are dislocations and twins. The former are line defects, the latter are surface defects, and both interact with acoustic waves. In this contribution, we briefly review recent progress in the implementation of ultrasound as a nonintrusive probe of dislocation and twin density in metals and alloys.