Thermal cycling induced δ to α phase transformation via an intermediate β phase on a δ-stabilized Pu–Ga alloy

The thermal cycling induced δ to α phase transformation in a δ-stabilised Pu–Ga alloy has been investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The alloy specimen was thermally cycled from 25 °C to 180 °C within the DSC furnace enabling coincident collection of phase transformation information. The cycling was carried out with varied isothermal hold periods at 25 °C between each DSC run. The α phase was detected in the original well-homogenised alloy and the amount of α phase was found to increase with both thermal cycling number and isothermal hold time. Nearly 8% α phase was detected after 210 cycles, with no sign that α phase in-growth had ceased or slowed. Possible mechanisms, by which thermal cycling facilitates the nucleation and in-growth of the increasing α phase content are discussed. It is hypothesised that the δ to α phase transformation proceeds via an intermediate β phase at elevated temperature. Based on this investigation, it is also suggested that thermal cycling may be used as a novel experimental method to study the meta-stable nature of δ-stabilized Pu alloys.

► Thermal cycling effect on the stability of Pu–Ga alloys was investigated.
► The amount of α phase was found to increase as a function of thermal cycles.
► The α phase in-growth had not ceased at the point where the study was terminated.
► The α phase increase is attributed to the δ to α transformation via intermediate β.
► Thermal cycling may be used to study the metastable nature of Pu–Ga alloys.