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

On the Potential for Vacancy Annihilation as a Mechanism for Conditioning in Pu-1.9at%Ga. J.R.Jeffries, K.J.M.Blobaum, A.J.Schwartz: Acta Materialia, 2009, 57[18], 5512-20