Effect of interfacial morphology on grain selection in unidirectional solidification

Grain selection during solidification is of importance to the processing of solidified structure. It plays an important role in unidirectionally solidified products such as turbine blade. In order to understand the effect of the interfacial morphology on grain selection in unidirectional solidification, an experimental work using transparent material and a mathematical modeling has been carried out. The number of grains (n) was found to decrease with increasing growth distance by the grain selection, depending upon the solid/liquid interfacial morphology. When the solid/liquid interface is dendritic, n rapidly decreases, on the other hand, when the solid/liquid interface is cellular, n slowly decreases. The reason for this may be that the growth direction of the cell is affected by heat flow and is closer to the heat flow direction than that of the dendrite. The mathematical model using Monte Carlo simulation for the grain selection has been developed. The change in growth direction with solid/liquid interfacial morphology has been first taken into account. Introducing the dimensionless growth direction (pi'), which is the ratio between growth direction and preferred growth direction, <100>, it is found that the mathematical model agrees well with the experimental results.