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Title: Thermodynamic Prediction of Compositional Phases Confirmed by Transmission Electron Microscopy on Tantalum-Based Alloy Weldments

Abstract

Tantalum alloys have been used by the U.S. Department of Energy as structural alloys for radioisotope based thermal to electrical power systems since the 1960s. Tantalum alloys are attractive for high temperature structural applications due to their high melting point, excellent formability, good thermal conductivity, good ductility (even at low temperatures), corrosion resistance, and weldability. Tantalum alloys have demonstrated sufficient high-temperature toughness to survive prolonged exposure to the radioisotope power-system working environment. Typically, the fabrication of power systems requires the welding of various components including the structural members made of tantalum alloys. Issues such as thermodynamics, lattice structure, weld pool dynamics, material purity and contamination, and welding atmosphere purity all potentially confound the understanding of the differences between the weldment properties of the different tantalum-based alloys. The objective of this paper is to outline the thermodynamically favorable material phases in tantalum alloys, with and without small amounts of hafnium, during and following solidification, based on the results derived from the FactSage(c) Integrated Thermodynamic Databank. In addition, Transition Electron Microscopy (TEM) data will show for the first time, the changes occurring in the HfC before and after welding, and the data will elucidate the role HfC plays in pinning grain boundaries.

Authors:
;  [1]; ;  [2]; ;  [3]
  1. BWXT Pantex, Amarillo, Texas 79120-0020 (United States)
  2. University of Dayton Research Institute, Dayton OH 45469-0102 (United States)
  3. Oak Ridge National Laboratory, Oak Ridge, TN 37831-6064 (United States)
Publication Date:
OSTI Identifier:
21054540
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 880; Journal Issue: 1; Conference: International forum-STAIF 2007: 11. conference on thermophysics applications in microgravity; 24. symposium on space nuclear power and propulsion; 5. conference on human/robotic technology and the vision for space exploration; 5. symposium on space colonization; 4. symposium on new frontiers and future concepts, Albuquerque, NM (United States), 11-15 Feb 2007; Other Information: DOI: 10.1063/1.2437460; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CORROSION RESISTANCE; DUCTILITY; GRAIN BOUNDARIES; HAFNIUM; HAFNIUM CARBIDES; MELTING POINTS; POWER SYSTEMS; RADIOISOTOPES; SOLIDIFICATION; SPACE; TANTALUM; TANTALUM ALLOYS; TEMPERATURE DEPENDENCE; THERMAL CONDUCTIVITY; THERMODYNAMICS; TRANSMISSION ELECTRON MICROSCOPY; WELDABILITY; WELDED JOINTS; WELDING; NESDPS Office of Nuclear Energy Space and Defense Power Systems

Citation Formats

Moddeman, William E., Birkbeck, Janine C., Barklay, Chadwick D., Kramer, Daniel P., Miller, Roger G., and Allard, Lawrence F.. Thermodynamic Prediction of Compositional Phases Confirmed by Transmission Electron Microscopy on Tantalum-Based Alloy Weldments. United States: N. p., 2007. Web. doi:10.1063/1.2437460.
Moddeman, William E., Birkbeck, Janine C., Barklay, Chadwick D., Kramer, Daniel P., Miller, Roger G., & Allard, Lawrence F.. Thermodynamic Prediction of Compositional Phases Confirmed by Transmission Electron Microscopy on Tantalum-Based Alloy Weldments. United States. doi:10.1063/1.2437460.
Moddeman, William E., Birkbeck, Janine C., Barklay, Chadwick D., Kramer, Daniel P., Miller, Roger G., and Allard, Lawrence F.. Tue . "Thermodynamic Prediction of Compositional Phases Confirmed by Transmission Electron Microscopy on Tantalum-Based Alloy Weldments". United States. doi:10.1063/1.2437460.
@article{osti_21054540,
title = {Thermodynamic Prediction of Compositional Phases Confirmed by Transmission Electron Microscopy on Tantalum-Based Alloy Weldments},
author = {Moddeman, William E. and Birkbeck, Janine C. and Barklay, Chadwick D. and Kramer, Daniel P. and Miller, Roger G. and Allard, Lawrence F.},
abstractNote = {Tantalum alloys have been used by the U.S. Department of Energy as structural alloys for radioisotope based thermal to electrical power systems since the 1960s. Tantalum alloys are attractive for high temperature structural applications due to their high melting point, excellent formability, good thermal conductivity, good ductility (even at low temperatures), corrosion resistance, and weldability. Tantalum alloys have demonstrated sufficient high-temperature toughness to survive prolonged exposure to the radioisotope power-system working environment. Typically, the fabrication of power systems requires the welding of various components including the structural members made of tantalum alloys. Issues such as thermodynamics, lattice structure, weld pool dynamics, material purity and contamination, and welding atmosphere purity all potentially confound the understanding of the differences between the weldment properties of the different tantalum-based alloys. The objective of this paper is to outline the thermodynamically favorable material phases in tantalum alloys, with and without small amounts of hafnium, during and following solidification, based on the results derived from the FactSage(c) Integrated Thermodynamic Databank. In addition, Transition Electron Microscopy (TEM) data will show for the first time, the changes occurring in the HfC before and after welding, and the data will elucidate the role HfC plays in pinning grain boundaries.},
doi = {10.1063/1.2437460},
journal = {AIP Conference Proceedings},
number = 1,
volume = 880,
place = {United States},
year = {Tue Jan 30 00:00:00 EST 2007},
month = {Tue Jan 30 00:00:00 EST 2007}
}
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