Ultrasonic scattering predictions for metal additive manufacturing

Abstract

Additive manufacturing (AM) of metals offers great promise for the creation of new engineering solutions because of the expanded design space offered by these new approaches. However, several challenges remain with respect to control of the spatial organization of the microstructure. The complex thermal cycles that drive the densification of material can result in dendritic grain growth, material texture, and residual stresses that must be quantified if a certified component is desired. Ultrasonic techniques have been shown to have the sensitivity and resolution necessary to play a major role in the metal AM inspections. The microstructural challenges present in AM samples have been examined, in many cases individually, but AM samples are especially complex. In this presentation, AM samples of 316 stainless steel created using laser powder bed fusion (LPBF) are studied ultrasonically in terms of their wave speed, attenuation, and diffuse backscatter characteristics. Electron backscatter diffraction (EBSD) measurements are used to create digital synthetics with statistically equivalent properties. The synthetics are then used to make ultrasonic predictions that are compared with the measurements. Prospects for in situ sample validation are then discussed.