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An investigation into the microstructure and weldability of a tantalum-containing cast cobalt-based superalloy

Abstract The weld metal microstructures and the weldability of a tantalum-containing cast cobalt-based superalloy were investigated using gas tungsten arc welding. It was found that the tantalum carbides in the base metal have remained stable up to the fusion line. The results showed that the formation of Ta-rich carbides (TaC) is very sensitive to time and temperature; so the as-weld microstructure is unstable from a metallurgical aspect. The formation of fine precipitates due to the high cooling rate of the welding process resulted in a weld metal with an undesirable hardness and microstructure after autogenous welding, especially after post weld heat treatment. Further results revealed that using a filler metal containing significantly less carbon and tantalum has solved the mentioned problems and made acceptable welds after post weld heat treatment.