Ultrasonic scattering in two-phase polycrystalline materials

Abstract

Typically, many of the polycrystalline materials found in nature and those created using different manufacturing processes consist of multiple phases. Careful nondestructive characterization of these materials is of fundamental importance for quality assurance because microstructure is strongly correlated with mechanical performance. Ultrasonic scattering measurements have shown high sensitivity to material microstructure such that this approach is of interest for multi-phase materials. A fundamental understanding of scattering from idealized two-phase materials would provide essential information regarding the predictive nature of scattering measurements to quantify such microstructures. For this purpose, samples were created using spark plasma sintering (SPS) from mixtures with three different ratios (with respect to mass) of Cu and Fe powders. These elements do not alloy such that the resulting samples will not have any intermediate phases. Moreover, one pure Cu sample and one pure Fe sample were also sintered using SPS. The samples were imaged using electron backscatter diffraction (EBSD) to quantify the material organization. Ultrasonic backscatter and attenuation measurements were performed on the samples and the results were used for comparison with scattering models. Prospects for nondestructive evaluation of such materials are also discussed. [Work supported by Air Force Research Laboratory (AFRL) under prime contract FA8650-15-D-5231.]