Creep Damage Mechanisms in Cast Cobalt Superalloys for Applications in Glass Industry

Abstract

Two cast NbC and TaC- strengthened cobalt-base superalloys have been developed for a precision casting of spinner discs for glass wool industry. In the present study, the relationships between the type and morphology of carbides and the degradation processes in both types of cast cobalt-based superalloys subjected to high temperature creep have been examined. It was found that the nature of carbides within the alloy microstructure plays a critical role in determining the creep damage processes and microstructure stability of the alloy system under high temperature creep. The morphology of the carbides is a strong function of their chemical composition. The interface decohesion between the complex carbides and the matrix and cracking of the brittle carbides homogeneously distributed in the crept NbC - strengthened alloy lead to brittle intergranular and/or interdendritic fracture. By contrast, Ta - strengthened alloy exhibited very small extent of isolated creep damage and the final fracture is ductile transgranular mode.