Structure and properties of a Pu-0.18Â wt.% Ga alloy

This study describes the characterisation of a cast plutonium-0.18 wt.% gallium (Pu-0.18 wt.% Ga) alloy, both in the as-cast condition as well as following an homogenising heat treatment. The alloy was subjected to density measurements, differential scanning calorimetry (DSC), dilatometry, optical microscopy, electron probe micro-analysis (EPMA), X-ray diffraction (XRD) and hardness measurements. The Ga content is insufficient to retain a wholly delta phase at ambient temperature. Instead, the alloy appears to be a mixture of alpha- and delta-Pu, which is borne out by density, dilatometry, DSC and XRD. Optical microscopy of the alloy following heat treatment revealed the microstructure to be composed of a two-phase mixture of alpha-Pu (α-Pu) and delta-Pu (δ-Pu). EPMA of the heat treated alloy shows the Ga content to be evenly distributed throughout the microstructure. The hardness of the heat treated alloy is approximately 25% lower than that of unalloyed Pu. No evidence supporting the presence of an amorphous Pu phase has been found.