Stress-induced phase transformation in shape memory ceramic nanoparticles

Abstract

Thermal treatment was observed to gradually transform the morphology of Ce0.12Zr0.88O2 (CZ) powder: transitioning from having round edges, to exhibiting clear facets, to particle growth, as a function of increasing treatment temperature. The effect of the morphological changes in the powder on the extent of stress-induced phase transformation upon mechanical compression is reported. The physical changes in the average particle size and the residual levels of monoclinic content (MC) post thermal treatment between 300 °C and 1550 °C are in line with the expectations. However, the extent of transformation upon compression is found to greatly depend on the thermal history of the powder, and generally, post compression, MC can be split into two regimes. Powders heat-treated below ∼1200 °C comprise regime 1, where post compression, MC increases as the preceding thermal processing temperature is increased. The increase in MC is despite the decreasing residual levels of the monoclinic phase in the CZ powder, which is caused by the thermal treatment. For the case of annealing above ∼1200 °C (comprising regime 2), stress-induced transformation becomes exceedingly difficult and the extent of the transformation is significantly reduced. The vital role played by the particle shape alone can be leveraged in the development of new applications of shape memory ceramics.