Study on the formation and competitive growth mechanism of stray grains during spiral grain selector of nickel-based single crystal superalloy

Abstract

Microstructure evolution and competitive grain growth in the spiral part of a single crystal sample whose crystal orientation deviating from the axial direction was analyzed. The results showed that the appearance of stray grains in the spiral part and the elimination of the originally preferred orientation grains by the competitive growth of stray grains are the reasons for the single-crystal orientation deviation defect. It was indicated that stray grains tend to nucleate at the initial stage of crystal selection in the spiral part. The inclined temperature gradient in the spiral part promoted the development of stray grains, whose growth direction was closer to the direction of the heat flow. Stray grains maintained the competitive growth in the spiral part, and a single crystal with the orientation deviated from the expected direction of 〈001〉 is formed.