Unidirectional solidification process and apparatus and single-crystal seed therefor

摘要

A single-crystal seed, apparatus and process for producing a casting having a single-crystal (SX) microstructure. The seed has a geometry that includes a vertex capable of destabilizing an oxide film that forms at the interface between the seed and a molten metal during the casting process, and thereby promotes a continuous single-crystal grain growth and reduces grain misorientation defects that can initiate from the seed/metal interface.

主权项

1. A process of unidirectionally casting an alloy, the process comprising:
providing a mold having a base and a mold cavity adjacent thereto; placing a single-crystal seed in the base of the mold, the seed comprising a body having a single-crystal microstructure and at least a first surface region, the first surface region defining a vertex of the body that protrudes away from the body; introducing a molten quantity of the alloy into the mold cavity; and then cooling the mold to cause unidirectional solidification of the molten quantity of the alloy within the mold and produce a unidirectionally-solidified casting having a columnar crystal structure, the molten quantity of the alloy contacting the seed so that the molten quantity epitaxially solidifies based on a crystallographic orientation of the seed, the vertex of the body of the seed destabilizing an oxide film forming on the first surface region as a result of surface tension of the oxide film at the vertex being sufficiently high to cause the oxide film to collapse as the oxide film is forming on the first surface region; wherein the first surface region of the body is a lateral surface of a conical portion of the body and the vertex is a point of the conical portion.