A regular solution model is fit to experimental equilibrium temperatures (T 0) and pressures (P 0) for diffusionless δ→α transformations in Pu-Ga and Pu-Al alloys, in order to define the chemical free energy change ΔG for δ→ α transformation. Analysis of reported isothermal δ→ αtransformation rate data in terms of nucleation-controlled martensitic kinetics gives a nucleation activation energy Q which is a nonlinear function of ΔG. The activation volume V * defined by δQ/δΔG is of the order of 10 to 40 atomic volumes, suggestive of rate control by an interfacial Peierls barrier. The grain size dependence of the transformation-start temperature at a fixed cooling rate of 2.08 × 10-2 Ks-1 is measured in a Pu-1.7 at. pct Ga alloy, revealing an inhibition of transformation at fine grain sizes. The overall kinetic behavior is characteristic of a martensitic mechanism.
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