Effect of shell temperature in thermal control solidification process on microstructure and stress rupture property of cast equiaxed superalloy

Abstract

Cast equiaxed superalloy is commonly used in the manufacture of engine turbine blades and complex structural castings due to its excellent casting properties and comprehensive mechanical properties. The more adaptable thermal control solidification process is usually used to refine the equiaxed crystal structure. In this paper, the microstructure and fracture surface of this alloy after solid solution were observed and characterized by means of OM, SEM, and EDS, and the effects of thermally controlled solidification processes with different shell temperatures on the microstructure and stress fracture properties of this alloy were investigated. The results showed that in this cast equiaxed crystal alloy, increasing the shell temperature from 1300 °C to 1330 °C causes the grain size to grow, microporosity to significantly decrease, and eutectic content and size to slightly increase. Both S1 and S2 alloys formed MC and M6C carbides after solid solution treatment. The size and content of carbides increased as the shell temperature rose, whereas the size and content of the γ’ phase decreased. As the shell temperature increases, the stress rupture properties increase slightly, while the degree of rafting increases dramatically. Cracks are mainly formed at the aggregation of microporosity, eutectics, and carbides. The reasons why cracks occur in the two alloys can differ. This study provides guidance for the design of a thermal control solidification process for cast equiaxed superalloys.