The effect of substrate orientation on stray grain formation in the (111) plane in laser surface remelted single crystal superalloys

Abstract

Ni-base single crystal (SX) superalloys exhibit high Young modulus along the [111] crystallographic orientation, and this raise the question that how to avoid stray grain formation during laser repair of surface defects in (111) plane if SX turbine component is cast in [111] direction. In this study, laser remelting was conducted in different substrate orientations in (111) plane and the susceptibility of equiaxed stray grain to substrate orientation was determined. We define an angle ξ to show the substrate orientation variation by which ξ = 0°, 30°, 60°, and 90° means the laser scanning direction along [112¯], [101¯], [21¯1¯], and [11¯0], respectively. It is found that with the increase of ξ, the susceptibility of equiaxed stray grain bottomed at 60° and then increases again. The theoretical calculated results confirm the experiment and show that it is caused by the ξ dependent variation in thermal gradient and dendrite growth velocity in different domains. We found that the optimized substrate orientation in (111) plane for laser remelting of SX superalloy is ξ = 60°. Our results can provide an in-depth insight into the mechanism how to avoid stray grain formation in the future laser repair of SX components.