Supporting evidence for double-C curve kinetics in the isothermal (delta) --> (alpha)' phase transformation in a Pu-Ga alloy
Time-temperature-transformation (TTT) diagrams for the {delta} {yields} {alpha}{prime} transformation in a number of Pu-Ga alloys were first reported in 1975 by Orme et al. Unlike typical single-C curve kinetics observed in most isothermal martensitic transformations, the Pu-1.9 at.% Ga alloy exhibits two noses, and thus double-C curve kinetics. The authors attributed the occurrence of the double C to a difference in mechanism: a massive transformation for the upper C and a martensitic transformation for the lower C. Since that time, the nature, and the existence of the double C have received only limited attention. The results of Deloffre et al. suggest a confirmation of this behavior, but the fundamental origin of the double C remains unknown. Here, we apply differential scanning calorimetry (DSC) as an alternative approach to acquiring the TTT data and our experimental evidence suggests a confirmation of the double-C behavior after 18 hours of isothermal hold time. In addition, we report three exothermic peaks corresponding to transformations during cooling at 20 C/min prior to the isothermal holds. These three peaks are reproducible and suggest a number of possibilities for the origin of the unique kinetics: {alpha}{prime} forms with different morphologies, or from different embryos in the upper and lower C curves; {alpha}{prime} forms directly in one C curve and forms via an intermediate phase in the other C curve; the two C curves result from {alpha}{prime} forming by two or more distinct mechanisms (e.g., massive and martensitic transformations).
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 951168
- Report Number(s):
- UCRL-JRNL-223221; JALCEU; TRN: US200911%%362
- Journal Information:
- Journal of Alloys and Compounds, Vol. 444-445; ISSN 0925-8388
- Country of Publication:
- United States
- Language:
- English
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