Laser Surface Modification of Single-Crystal Nickel-Based Superalloy: Geometry, Microstructure, Crack Morphology, and Microhardness

The present work investigates the surface modification of a second-generation, SX nickel-based superalloy by using a continuous wave laser with various laser powers under the conductive mode of heat penetration. The aim was to reduce the surface strength to improve the machinability. The results show that the laser surface modified (LSM) geometry and their surface irregularities increase with an increase in laser power. The cross section of the LSM geometry under lower powers is semi-elliptical in shape, whereas it becomes a top-hat shape under higher laser powers. Fine dendrites of around 10 µm with various morphologies are formed in the LSM geometry. The dendrite size increases with an increase in laser power except at the highest laser power. The LSM geometry consists of longitudinal and transverse cracks along the scanning direction. The longitudinal cracks are formed near the centerline at lower laser powers, whereas the transverse cracks are formed at a faraway distance from the centerline at higher laser powers. The longitudinal cracks have vertical cracking and transverse cracks have zig-zagged cracking beneath the surface. The total crack length increases with an increase in laser power. The LSM interface consists of dense micropores and microcracks at the inter-dendric region. However, the LSM region consists of lesser microsegregation and fine dendrites than the base metal, its microhardness is lower than the base metal due to the formation of laser-induced defects.