Effects of Groove Shape on Microstructure and Mechanical Responses of Laser-Directed Energy Deposition-Repaired GH4099 Ni-Based Superalloy

Repairing the Ni-based superalloy component remains challenging due to the limited understanding of the role of the defect’s morphology on microstructure and related deformation responses. To address this issue, GH4099 Ni-based superalloy plate with U-shaped and V-shaped grooves was prepared and repaired by laser-directed energy deposition method using GH4099 powders. Both grooves exhibit three similar regions at the repaired interphase, which are the base metal region with equiaxed grains, repaired region with columnar or elongated equiaxed grains, and a transition region in between. High-temperature gradient in the repaired region induced a high density of substructures, and the repaired region in U-shaped grooves has an even higher temperature gradient due to fewer passes of the melted metal, which induces more metallic carbides in the subgrain boundaries and improves the tensile strength of the repaired samples. However, due to the steep side walls, local vortex might form at the bottom corner of the U-shaped groove, leaving macroscale holes and micro-cracks there. Such defects will decrease the alloy’s ductility. The relationship among groove morphology–macro- and microstructure–mechanical properties is then established, which suggesting the preferred V-shaped groove considering the flatter sidewall and more passes induced near equilibrium microstructure.