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

Abstract

The complexity of phase stability and transformations in plutonium alloys is reflected in the plutoniumgallium (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.

Orientation Relationship, Habit Plane, Twin Relationship, Interfacial Structure, and Plastic Deformation Resulting from the δ → α′ Isothermal Martensitic Transformation in Pu-Ga Alloys

“…[14] (b) and (c) Two TEM images showing the background density of dislocations in d-Pu and the density near the tip of an a¢ plate, which differ by a factor of 7 to 8. without annealing, the cycles do become increasingly displaced. [19] However, when the samples are annealed after a low-temperature experiment and then conditioned at room temperature for at least 6 hours, they exhibit the same traces upon multiple runs. [20] For small grains to be consumed by larger ones and to have appreciable grain growth occur, considerable annealing must take place at high temperature and for long periods.…”

Evidence of transformation bursts during thermal cycling of a Pu-Ga alloy

“…Upon heating, a' reverts to d, but the temperature span of the thermal hysteresis is quite large, approximately 150°C, depending on the alloy composition. Recent work indicates that this reversion exhibits an unusual succession of sharp peaks in differential scanning calorimetry (DSC) scans, [10][11][12] and corresponding discrete, incremental steps in dilatometry 13 and resistometry 12 plots, which suggest autocatalytic burst martensite events. It is the nature of the d ‡ a' martensitic transformation, and its corresponding reversion, that we focus on here.…”

Orientation Relationship, Habit Plane, Twin Relationship, Interfacial Structure, and Plastic Deformation Resulting from the δ → α′ Isothermal Martensitic Transformation in Pu-Ga Alloys

“…[14] (b) and (c) Two TEM images showing the background density of dislocations in d-Pu and the density near the tip of an a¢ plate, which differ by a factor of 7 to 8. without annealing, the cycles do become increasingly displaced. [19] However, when the samples are annealed after a low-temperature experiment and then conditioned at room temperature for at least 6 hours, they exhibit the same traces upon multiple runs. [20] For small grains to be consumed by larger ones and to have appreciable grain growth occur, considerable annealing must take place at high temperature and for long periods.…”