Significance of heterogeneous surface growth in up-gradient and stationary-gradient crystallization

Gradient crystallization methods have been proposed and studied for creating microstructures which exhibit crystal orientation. For many of these processes it is possible for spurious heterogeneous nucleation and growth to occur from the sample sides and compete with desired oriented growth. We analyze this growth interference effect for two methods of crystallizing in a temperature gradient: either moving up a temperature gradient, or crystallizing in a stationary temperature gradient. It is demonstrated that the up-gradient technique is mainly suited to relatively long, narrow samples (with some restrictions), while the stationary gradient process is preferred when crystallizing normal to the large face of slab shaped samples. Limitations which constrain both of these gradient crystallization techniques are discussed.