Optimizing the Diffusion Welding Process for Alloy 800H: Thermodynamic, Diffusion Modeling, and Experimental Work

摘要

A research effort was made to evaluate the usefulness of modern thermodynamic and dif fusion 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 assem bling 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 prop erty 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.