Optimizing the Diffusion Welding Process for Alloy 800H: Thermodynamic, Diffusion Modeling, and Experimental Work
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A research effort was made to evaluate the usefulness of modern thermodynamic and diffusion computational tools, Thermo-Calc and Dictra (Thermo_Calc Software, Inc., McMurray, PA), in optimizing the parameters for diffusion welding of Alloy 800H. This would achieve a substantial reduction in the overall number of experiments required to achieve optimal welding and post-weld heat treatment conditions. This problem is important because diffusion-welded components of Alloy 800H are being evaluated for use in assembling compact, micro-channel heat exchangers that are being proposed in the design of a high-temperature, gas-cooled reactor by the U.S. Department of Energy. The modeling was done in close contact with experimental work. The latter included using the Gleeble 3500 System (Dynamic Systems, Inc., Poestenkill, NY) for welding simulation, mechanical property measurement, and light optical and scanning electron microscopy. The modeling efforts suggested a temperature of 1423 K (1150 °C) for 1 hour with an applied pressure of 5 MPa using a 15-μm Ni foil as joint filler to reduce chromium oxidation on the welded surfaces. Good agreement between modeled and experimentally determined concentration gradients was achieved, and model refinements to account for the complexity of actual alloy materials are suggested.
KeywordsWelding Diffusion Couple Filler Metal Sigma Phase Weld Interface
The authors would like to express gratitude to the Next Generation Nuclear Plant (NGNP) Program Management (Messrs Michael Patterson and Charles Park) at INL for their continuous support of this research effort. The work was supported through the U.S. Department of Energy, Office of Nuclear Energy, Science, and Technology, under DOE Idaho Operations Office Contract DE-AC0799ID13727. The authors would like to acknowledge Todd Morris for metallurgical support. One of the authors (M.V.G.) would like to extend his most sincere gratitude to Dr. Carolyn Campbell (NIST) for her generous support of our initial modeling efforts. We are also very grateful to Prof. Zi-Kui Liu and Prof. Long-Qing Chen (both of Penn State University) for the valuable discussions, and to Prof. John E. Morral (of Ohio State University) for the useful discussion of the obtained results.
This submitted manuscript was authored by a contractor of the U.S. Government under DOE Contract No. DE-AC07-05ID14517. Accordingly, the U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for U.S. Government purposes.
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