Phase transformations in PuGa 1 at.% alloy: Study of whole reversion process following martensitic transformation

The purpose of this work was to study PuGa 1 at.% alloy behavior from martensitic transformation to the whole reversion process. The relevant phase transformations were investigated as a function of temperature via in situ X-ray diffraction and dilatometry analyses carried out at low and high temperatures. The results show that the delta-to-alpha' martensitic transformation occurring at low temperatures is direct and does not involve any intermediate gamma' phase. They also reveal that the reverse transformation of the two-phase d delta-to-alpha' alloy during heating involves two competing modes, namely direct and indirect reversion. The latter is associated with a Ga diffusion process that governs the ratio between these reversion modes. More precisely, our study demonstrates that the indirect reversion process consists of a Ga-enrichment of the remaining delta phase as well as the emergence of the beta and gamma phases of pure plutonium. Every stage of indirect reversion has been discussed in relation to the equilibrium phase diagram of the Pu-Ga binary system. (C) 2013 Elsevier B.V. All rights reserved.