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“Burst-like” Characteristics of the δ/α′ Phase Transformation in Pu-Ga Alloys

  • Kerri J.M. Blobaum (a1), Christopher R. Krenn (a1), Jeffery J. Haslam (a1), Mark A. Wall (a1) and Adam J. Schwartz (a1)...

Abstract

The δ to α′ phase transformation in Pu-Ga alloys is intriguing for both scientific and technological reasons. On cooling, the ductile fcc δ-phase transforms martensitically to the brittle monoclinic α′-phase at approximately −120°C (depending on composition). This exothermic transformation involves a 20% volume contraction and a significant increase in resistivity. The reversion of α′ to δ involves a large temperature hysteresis and begins just above room temperature. In an attempt to better understand the underlying thermodynamics and kinetics responsible for these unusual features, we are examining the δ/α' transformations in a Pu-0.6 wt% Ga alloy using differential scanning calorimetry (DSC) and resistometry. Both techniques indicate that the martensite start temperature is −120°C and the austenite start temperature is 35°C. The heat of transformation is approximately 3 kJ/mole. During the α ′ → δ reversion, “spikes” and “steps” are observed in DSC and resistometry scans, respectively. These spikes and steps are periodic, and their periodicity with respect to temperature does not vary with heating rate. With an appropriate annealing cycle, including a “rest” at room temperature, these spikes and steps can be reproduced through many thermal cycles of a single sample.

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“Burst-like” Characteristics of the δ/α′ Phase Transformation in Pu-Ga Alloys

  • Kerri J.M. Blobaum (a1), Christopher R. Krenn (a1), Jeffery J. Haslam (a1), Mark A. Wall (a1) and Adam J. Schwartz (a1)...

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