Ultrasonic characterization of cold sintered ZnO components with varying relative densities

Abstract

The cold sintering process is a low temperature processing technique used to synthesize metals, ceramics, and composites. Some cold sintered parts do not reach the mechanical properties of conventionally sintered parts even at high relative densities. These diminished mechanical properties are presumed to be in part a result of either in inhomogeneous removal of transient liquid phases or inability to reach the proper cold sintering temperature/pressure everywhere in the part. In this presentation, we evaluate the spatial variability in the properties of cold sintered ZnO parts with decreasing relative densities through ultrasonic testing. The presence of homogeneously distributed porosity is assessed by ultrasonic wave speed, while macro-flaws larger than the average pore size are assessed through ultrasonic attenuation. The results are compared to the response of conventionally sintered ZnO samples with densities ranging from 86% to 89%. Conventionally sintered and cold sintered parts exhibited different slopes in the decrease of wave speed with density. This difference suggests microstructural discrepancies beyond porosity in cold versus conventionally sintered ZnO components. Attenuation results suggested the presence of macro-flaws even in the samples with highest relative density. These results underscore the importance of nondestructive characterization of the cold sintered components.