Effect of substrate orientation on the formation of equiaxed stray grains in laser surface remelted single crystal superalloys: Experimental investigation

Abstract

Substrate orientation could play a key role in the stray grain (SG) formation in laser welded single crystal (SX) alloys, which is critical to a successful repair of SX components. In a previous work [Acta mater 2015; 88:283–292], we studied theoretically the substrate orientation effect on equiaxed SG susceptibility in laser melt pools by altering the orientation via rotations around x-, y-, and z-axis, which coincide with the [100], [010], and [001] crystallographic directions, respectively. It was found that y-axis rotation leads to a strong variation in SG ability whereas x- and z-axis rotations nearly have no effect. In this study, experiments were conducted to verify the calculated results. DD6, a second-generation Chinese SX superalloy was chosen as the object of research. The orientation-dependent SG formation was determined and the area-average volume fraction of SGs was employed to evaluate the overall CET tendency. The experimental tendency of the orientation dependent SG agrees well with the theoretical prediction. The effect of the substrate orientation on SG formation was further revealed by cosψ distribution, where ψ is a geometrical parameter which is the angle between normal vector to the solidification front and preferred crystallographic direction in dendrite domain. Our results provide an in-depth insight into the control of laser processing window for SX repair via adjusting the substrate orientation.