Utilization of Ultrasonic Measurements to Quantify Aging-Induced Material Microstructure and Property Changes

Abstract

AbstractMany structural components are exposed to thermal environments that promote aging-induced changes in material microstructure and properties. The extent of these changes may lead to a reduction in the design safety factors and, as a worst case, premature failure of the component. In order to illustrate how nondestructive measurements can be used to indicate these changes, ultrasonic measurements were conducted on stainless steel. Specimens from a high-carbon, Type 304 stainless steel were subjected to various thermal treatments to introduce differing precipitation morphologies. Specimens were examined using transmission electron microscopy to quantify the size, density, and distribution of the precipitates formed. Ultrasonic measurements were performed to assess sensitivity to the change in precipitation levels. Shear-wave birefringence provided the most consistent measurements for tracking precipitate morphology changes. Birefringence velocity differences increased as precipitate size and density increased on grain boundaries and as additional precipitates formed in the matrix. The ability to nondestructively monitor the precipitation process is important since susceptibility to environmentally assisted cracking and low-temperature embrittlement correlated with this microstructural change.