On the potential for vacancy annihilation as a mechanism for conditioning in Pu-1.9 at.% Ga

The δ→α′ martensitic transformation in Pu-1.9 at.% Ga occurs when the alloy is cooled below about −100 °C. This transformation is isothermal and exhibits a remarkable susceptibility to an ambient-temperature isothermal hold (referred to as conditioning) prior to the transformation. This “conditioning” effect can dramatically increase the amount of transformation that occurs at low temperature; however, the mechanism by which conditioning affects the δ→α′ transformation is not known. This conditioning effect may be a more general phenomenon, and thus knowledge of the mechanism responsible for conditioning is of great importance to understanding the δ→α′ transformation itself as well as the general circumstances that can affect martensitic phase transformations. Using differential scanning calorimetry measurements, vacancy annihilation as a mechanism for the conditioning effect has been examined. While there are some characteristics of the conditioning effect that are reminiscent of vacancy annihilation, the results of these experiments suggest that vacancy annihilation is not a likely candidate description for the conditioning effect.