Anomalous Mechanical Responses in Flash-Processed Ceramics

Abstract

Flash events, where high-temperature dynamics such as sintering, superplasticity, and crack healing of ceramics are significantly promoted by electric fields and/or currents, have been attracting scientific and technological interests. In this review, anomalous mechanical responses in 8 mol% yttria-stabilized zirconia flash-processed using an AC electric field are described. The dynamic and quasi-static mechanical properties before and after flash processing were evaluated via sound velocity and nanoindentation measurements to characterize the mechanical responses attributed to flash-induced defects. Rate-dependent elastic softening (i.e., the slower the loading rate, the lower the indentation modulus) was observed in the quasi-static range after flash processing, while a negligible change was confirmed in the dynamic elastic behaviors even after flash. Such anomalous mechanical responses in the flash-processed sample are characterized as anelasticity (i.e., viscoelasticity or pseudoelasticity in other terms), which can be attributed to stress-induced and thermally activated recoverable motions of point defect dipoles induced via flash processing. This anelastic behavior may be of importance for understanding the nature of flash-induced defects which athermally contribute to the enhanced diffusion during flash events.