Comprehensive influence of Y on K417 superalloy: Purification, interactions among the alloy elements and high temperature properties

This study investigated the effects of yttrium addition (0wt%-0.5wt%) on the purification, microsegregation and mechanical properties of K417 cast superalloy. The results showed that the addition of Y could significantly reduce the content of oxygen. Purified K417 superalloy with 4 similar to 7ppm O content was obtained after adding a moderate amount of Y. With the increasing Y addition, the segregation degrees of alloying elements (Ti, V and Mo) dropped as a whole, gamma' phase was refined, and the size and volume fraction of gamma/gamma' eutectic increased. The decrease in the degree of Ti segregation and the solid solution of Y in carbide periodicity changed the morphology of carbide. When the Y addition increased from 0wt% to 0.1 wt%, the decrease of O content, the refinement of gamma' phase and the formation of rod carbides increased the high temperature tensile strength of the alloy. When the Y addition increased from 0.2wt% to 0.5 wt%, the production of large-size Y-rich phase reduced the mechanical properties of the alloy. The plasticity of the alloy rised and then decreased with increasing Y addition. The appropriate amount of Y addition was about 0.01wt% to 0.05wt%.