Enhanced Epitaxial Growth of Columnar Crystal in Laser Repaired Single Crystal Superalloys on Non-(001)-Oriented Surfaces

Author of the article:WANG Lei, HE Feng, WANG Zhijun, LI Junjie, WANG Jincheng

Author's Workplace：State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072, China

Key Words：single-crystal superalloy; laser repair; growth region distribution; stray grain formation

Abstract：Epitaxial crystal in dendritic form grows along the crystallographic direction of a substrate and can be misoriented with respect to the heat flow direction. This point needs to be considered during the repair of valuable single crystal components with laser metal forming/deposition techniques. During the process, achieving epitaxial structures without nucleated grains is required to maintain single crystal integrity, which is achieved on (001)-oriented planes. However, randomly oriented surfaces can be encountered in real applications that need to be examined. In this work, the repairs on (001)- and non- (001)-oriented surfaces are studied comparatively, with a focus on the avoidance of nucleated grains. The local solidification variables that control the deposited structures are calculated, and the fraction of nucleated grains is quantified as an index of single-crystal integrity. The results show that enhanced epitaxial growth can be achieved on most non-(001) planes compared to the (001) surface, which is also verified by our experiments. This difference can be related to the boundaries of different dendritic growth regions as well as their locations. It is expected that the results can be applied to optimize deposition orientations and laser processing windows in repair and manufacturing applications.