Evidence of Transformation Bursts During Thermal Cycling of a Pu-Ga Alloy

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The thermodynamics and kinetics of the fcc (delta) to monoclinic (alpha-prime) phase transformation and its reversion in a plutonium-gallium alloy have been studied using differential scanning calorimetry, resistometry, and dilatometry. Under ambient conditions, the delta phase is metastable in a Pu-2.0 at% Ga alloy. Thermal cycling to below the ambient temperature results in a partial transformation to the alpha-prime phase; this transformation is composition-invariant and exhibits martensitic behavior. Because this transformation results in an unusually invariant large 25% volume contraction that cannot be fully accommodated by purely elastic adjustments, the transformation mode is expected to involve burst formation of individual ... continued below

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Blobaum, K M; Krenn, C R; Mitchell, J N; Haslam, J J; Wall, M A; Massalski, T B et al. February 9, 2005.

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The thermodynamics and kinetics of the fcc (delta) to monoclinic (alpha-prime) phase transformation and its reversion in a plutonium-gallium alloy have been studied using differential scanning calorimetry, resistometry, and dilatometry. Under ambient conditions, the delta phase is metastable in a Pu-2.0 at% Ga alloy. Thermal cycling to below the ambient temperature results in a partial transformation to the alpha-prime phase; this transformation is composition-invariant and exhibits martensitic behavior. Because this transformation results in an unusually invariant large 25% volume contraction that cannot be fully accommodated by purely elastic adjustments, the transformation mode is expected to involve burst formation of individual alpha-prime particles. However, upon cooling, these individual bursts were not resolved by the above techniques, although signals corresponding to the overall accumulation of many alpha-prime particles were observed. On the other hand, upon heating, signals from differential scanning calorimetry, resistometry, and dilatometry showed a series of discrete changes occurring in periodic increments beginning at approximately 32 C. These features correspond to the cooperative reversion of many alpha-prime particles to the delta phase; they appear to be the result of an interplay between the autocatalytically driven reversion of a cascade of individual martensite units, and self-quenching caused by small changes of temperature and/or stress accompanying each individual transformation burst. The heat of the delta/alpha-prime transformation is estimated to be about + 4 kJ/mole.

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PDF-file: 39 pages; size: 4.2 Mbytes

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  • Journal Name: Metallurgical and Materials Transactions A; Journal Volume: 37A

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  • Report No.: UCRL-JRNL-209611
  • Grant Number: W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 883811
  • Archival Resource Key: ark:/67531/metadc875423

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  • February 9, 2005

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  • Sept. 21, 2016, 2:29 a.m.

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  • Nov. 28, 2016, 1:47 p.m.

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Blobaum, K M; Krenn, C R; Mitchell, J N; Haslam, J J; Wall, M A; Massalski, T B et al. Evidence of Transformation Bursts During Thermal Cycling of a Pu-Ga Alloy, article, February 9, 2005; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc875423/: accessed August 21, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.