Phase stability and phase transformations in plutonium and plutonium-gallium alloys

The complexity of phase stability and transformations in plutonium alloys is reflected in the plutonium-gallium (Pu-Ga) phase diagram, which is perhaps the most complex of all binary systems. Although many investigations have explored phase equilibria, transformation systematics, and structure/property relations in the Pu-Ga system, many outstanding problems remain and new issues regularly appear. In this article, we describe recent dilatometry and calorimetry measurements on pure plutonium and plutonium-gallium alloys. We also present recent phase diagram modeling that attempts to unravel differences between the U.S. and Russian Pu-Ga phase diagrams. The ultimate goal of this work is to produce the first internally consistent database of thermophysical properties of this system so that a true equilibrium phase diagram can be produced and so that stability can be predicted over a range of conditions. This article is based on a presentation in the symposium “Terence E. Mitchell Symposium on the Magic of Materials: Structures and Properties” from the TMS Annual Meeting in San Diego, CA in March 2003.