System and method of making single-crystal structures through free-form fabrication techniques

Abstract

A single-crystal structure is grown using free-form fabrication through principles of directional solidification and direct-deposition techniques. The structure is formed from a metallic alloy by building from feedstock on top of and upward from a heated base element. The top of the structure is also heated with a scanning beam as it is built. The higher temperatures near the melting alloy tend to promote crystal growth rather than nucleation as the grain grows toward the heat of the scanning beam. This allows a two-dimensional thermal gradient to be formed in the build direction, which allows the solid crystal to maintain one orientation during the deposition process. As the material initially solidifies, it nucleates off of a desired grain that is designated by a grain selector. This method eliminates the need for expensive mold cavities and segmented furnaces that are typically required by prior art processes for producing some components.