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Probing the isothermal δ→α' martensitic transformation in Pu-Ga with in situ x-ray diffraction

Published online by Cambridge University Press:  01 February 2011

Jason R. Jeffries
Affiliation:
jeffries4@llnl.gov, Lawrence Livermore National Laboratory, Livermore, California, United States
Kerri J.M. Blobaum
Affiliation:
blobaum1@llnl.gov, Lawrence Livermore National Laboratory, Livermore, California, United States
Adam J. Schwartz
Affiliation:
schwartz6@llnl.gov, Lawrence Livermore National Laboratory, Livermore, California, United States
Hyunchae Cynn
Affiliation:
cynn1@llnl.gov, Lawrence Livermore National Laboratory, Livermore, California, United States
Wenge Yang
Affiliation:
wyang@hpcat.aps.anl.gov, HPCAT, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
William J. Evans
Affiliation:
evans31@llnl.gov, Lawrence Livermore National Laboratory, Livermore, California, United States
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Abstract

The time-temperature-transformation (TTT) curve for the δ → α′ isothermal martensitic transformation in a Pu-1.9 at. % Ga alloy exhibits an anomalous double-C curve. Recent work suggests that an ambient temperature conditioning treatment enables the lower-C curve. However, the mechanisms responsible for the double-C are still not fully understood. When the δ → α′ transformation is induced by pressure, an intermediate γ′ phase is observed in some alloys. It has been suggested that transformation at upper-C temperatures may proceed via this intermediate phase, while lower-C transformation progresses directly from δ to α′. To investigate the possibility of thermally induced transformation via the intermediate γ′ phase, in situ x-ray diffraction at the Advanced Photon Source was performed. Using transmission x-ray diffraction, the δ → α′ transformation was observed as a function of time and temperature in samples as thin as 30 μm. The intermediate γ′ phase was not observed at -120°C (upper-C curve) or -155 °C (lower-C curve). Results indicate that the bulk of the α′ phase forms relatively rapidly at -120 and -155 °C.

Type
Research Article
Copyright
Copyright © Materials Research Society 2010

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