Effect of directional solidification methods on solid solution window in Ni-based single-crystal superalloy

Abstract

In this work, the effect of directional solidification methods on solid solution windows in two Ni-based single-crystal superalloys is investigated. The sample prepared using the liquid metal cooling (LMC) method was found to contain smaller dendrite spacing, lower dendrite segregation and eutectic, and a smaller size of γ′ phase than that of the high-speed rapid solidification (HRS) method. The alloy-2 contained higher Cr, Co and lowered Re exhibited similar dendrite spacing and volume fraction of eutectic, and the lower dendrite segregation and smaller size of γ′ phase than that of the other alloy-1. The solution treatment window is broadened by adopting the LMC method or changing the composition to alloy-2. This is mainly realized by decreasing the lower limit temperature, and the upper limit temperature remains unchanged. According to the eutectic only contains the melt temperature, a similar eutectic is responsible for the unchanged upper limit temperature. At this state, the lower bound of the temperature is the dissolution of the γʹ phase in the dendrite core. The smaller size of γ′ phase and the elements' partition ratio are responsible for the change in the solid solution window.