RESEARCH ON DIVERGED BI-CRYSTAL COMPETITIVE GROWTH IN DIRECTIONAL SOLIDIFICATION

Abstract

Grain selection in directional solidification is a fundamental process in single-crystal super alloy production. In fact, many factors can influence this process. This work only focuses on the effect of pulling rates on competitive divergence in directional solidification. The competitive growth of bi-crystal at different pulling rates was observed during 2D directional solidification using the transparent model alloy SCN-1.7%Eth (mass fraction). The results show that as the pulling rate increases, it becomes harder for preferred grain to eliminate slant grain. This is because the increase of pulling rate decreases primary dendrite arm spacing and slightly reduces the frequency of new primary dendrite arms. When the growth direction of preferred grain is not well aligned with temperature gradient, the preferred grain can also be eliminated by the slant grain at specific pulling rates.