Abstract: Insulating material is applied in selected mold surfaces and in critical thicknesses to prevent cracking of the mold and casting therein during the heating and cooling steps of high rate directional solidification processes.

Abstract: Directional solidification of a single crystal superalloy article may be accomplished using a mold with a starter section, and a selector section to convert columnar growth from the starter into single crystal growth. In such a process, the deviation of [001] crystallographic orientation with respect to the longitudinal axis of the article being formed is reduced from 9 degrees to 5 degrees by controlling the heat transfer in the starter section. A stepped starter section, wherein the lower subsection has a volume of 52-98% of the total starter volume, and wherein the upper subsection is relatively small in lateral dimension, has been found most useful. When the solidification interface moves into the smaller width upper subsection, it becomes more nearly planar, and results in improved columnar growth in the starter, and in reduction in the crystallographic deviation of the article.