Study of the γ → δ phase transformation kinetics and reaction mechanism in plutonium

•Performed non-isothermal kinetic analysis of γ → δ phase transformation in plutonium.•Activation energy profiles established following different thermal conditions.•Examined the γ → δ phase transformation parameters under different thermal conditions.•Proposed a mechanism for the γ → δ phase transformation based on the kinetic analysis.•Physical properties of the parent γ-phase impact on nucleation and growth of δ-phase.

This work establishes the kinetics and reaction mechanism for the γ → δ phase transformation in plutonium under non-isothermal conditions and examines the phase transformation parameters under conditions that have not previously been considered.The thermal history and condition of a specimen will have a significant effect on the reaction parameters of a solid phase transformation. The current work examines the influence of the specimen condition and more specifically the impact of a previous phase transformation on the γ → δ phase transformation parameters and kinetics. The γ → δ phase transformation parameters and activation energy profile were determined both immediately following the previous phase transformations and following an isothermal hold in the γ-phase (50 h at 260 °C) to allow the specimens to recover from the impact of the previous phase transformations.A reaction mechanism for the γ → δ phase transformation is proposed based on the kinetic and mechanistic analysis. This transformation mechanism describes how the difference in structure and physical properties of the parent γ-phase affects the nucleation and growth of the δ-phase.