SUMMARY

Nonlinear ultrasound (NLU) inspection techniques have been shown to be effective in detecting second-phase precipitation in steel alloys. The aim of this research is to develop a model that quantitatively links the growth of grain boundary precipitates in steel to the evolution of the classical nonlinearity parameter β. The model is developed for the growth of M23C6 carbides in austenitic stainless steel, linking the development of misfit dislocations at the semicoherent phase boundary interface to growth in β. The predictions generated through precipitate growth modeling in conjunction with physics-based acoustic models are confirmed by microstructural characterizations and experimental measures of nonlinearity. This overall approach is then demonstrated in Fe-1%Cu and 9Cr-1Mo stainless steel alloys, and nonlinearity models are assessed for each alloy.