THERMODYNAMICS AND KINETICS OF PHASE TRANSFORMATIONS IN PLUTONIUM ALLOYS - PART I

Technical Report · Wed Aug 18 00:00:00 EDT 2004

DOI:https://doi.org/10.2172/895082· OSTI ID:895082

Turchi, P A; Kaufman, L; Liu, Z; Zhou, S

In this report we investigate order, stability, and phase transformations for a series of actinide-based alloys. The statics and kinetics of precipitation and ordering in this class of alloys are modeled with a scheme that couples fundamental information on the alloy energetics obtained from experimental and assessed thermo-chemical data to the CALPHAD approach commonly used in industry for designing alloys with engineering specificity with the help of the Thermo-Calc software application. The CALPHAD approach is applied to the study of the equilibrium thermodynamic properties of Pu-based alloys, Pu-X, where X=Al, Fe, Ga. The assessment of the equilibrium phase diagrams in the whole range of alloy composition has been performed with the PARROT module of the Thermo-Calc application software. Predictions are made on the low temperature and Pu-rich side of the phase diagrams of Pu-Ga and Pu-Al for which controversy has been noted in the past. The validity of the assessed thermo-chemical database will be discussed by comparing predicted heats of transformation for pure Pu with measured values from differential scanning calorimetry analysis. An overall picture for the stability properties of Pu-Ga and Pu-Al that reconciles the results of past studies carried out on these alloys is proposed. Results on phase stability in the ternary Fe-Ga-Pu and Al-Fe-Pu alloys are discussed. The information collected in this study is then used to model metastability, long-term stability and aging for this class of alloys by coupling Thermo-Calc with DICTRA, a series of modules that allow the analysis of DIffusion Controlled TRAnsformations. Kinetics information is then summarized in so-called TTT (temperature-time-transformations) diagrams for the most relevant phases of actinide alloys. Specifically, results are presented on kinetics of phase transformations associated with the eutectoid-phase decomposition reaction occurring at low temperature, and with the martensitic transformation that takes place at low Ga content in Pu-Ga alloys. Finally, after a summary of the most salient results, suggestions are made for further studies at the micro- and mesoscales.

• Research Organization: Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 895082
• Report Number(s): UCRL-TR-206658; TRN: US200702%%603
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ACTINIDE ALLOYS
AGING
ALLOYS
CALORIMETRY
DIFFUSION
KINETICS
PHASE DIAGRAMS
PHASE STABILITY
PHASE TRANSFORMATIONS
PLUTONIUM ALLOYS
PRECIPITATION
SPECIFICITY
STABILITY
THERMODYNAMIC PROPERTIES
THERMODYNAMICS
TRANSFORMATIONS