Effect of micro-grain casting process on the microstructure and high cycle fatigue properties of K492M alloy at 700 °C

Abstract

A nickel base polycrystalline superalloy K492M was used as the material in the present study. The samples of K492M alloy were prepared by conventional casting process, fine-grain casting process and micro-grain casting process, respectively, to study the effects of micro-grain casting process on the microstructure and high cycle fatigue property of K492M alloy at 700 °C. The experimental results show that micro-grain casting process can significantly refine grains, reduce solidification segregation and increase γ′ volume fraction. The micro-grain casting K492M sample exhibited a significantly higher high cycle fatigue life at 700 °C, which was improved by 412% and 269% from that of conventional and fine-grain casting samples, respectively. Analysis for fracture sample indicated that fatigue cracks initiated from the persistent slip bands on the surface or subsurface of the sample. In addition, the cracked carbides accelerated the crack propagation and fatigue fracture. The refined grains and carbides by micro-grain casting process significantly slowed down the propagation of fatigue cracks, and thereby improves the fatigue life.