Possible mechanism of spurious grain in single crystal casting process

A 2-D grain selection model has been developed to simulate the transition from chill to columnar zone. A calculated result agrees well with the experimental results, which have been reported in MCSP4. This model has been applied to the single crystal casting process. The yield rate of well-oriented single crystal increases with increasing the nucleation density on the chill plate. However, the yield rate does not reach 100%. There are following two cases to remain the spurious grains. The first case is that there is an inclined grain in the edge and this is not overgrown during grain section. The second case is that there are diverging or converging grains in the middle of the cast and the grain boundary of these grains is almost parallel to the growth direction. Since these phenomena may happen accidentally, the yield rate does not reach 100%.