Experimental Study on Laser-Induced Surface Damage of a Single-Crystal Nickel-Based Superalloy Under Continuous Wave Fiber Laser Scanning Process

Abstract

Single-crystal (SC) nickel-based superalloy castings offer high-temperature mechanical properties that result in superior gas turbine engine performance and durability. These castings undergo various precision machining operations to remove a significant amount of material while manufacturing. Here, nickel-based superalloys are one of the most difficult materials to be cut. Therefore, novel concepts are being employed to improve their machinability including lowering their surface strength. This paper presents the introduction of laser-induced surface damage (LISD) on a second-generation SC nickel-based superalloy using a continuous wave (CW) fiber laser. Laser scanning experiments were performed on SC specimens in the as-cast condition with a laser power of 1000 W, a beam diameter of 1.2 mm, and scanning speeds from 5.5 mm/s to 16.5 mm/s. The cross-sections of the laser-irradiated surfaces were investigated by measuring the irradiated geometries (IRG), microstructural changes, microsegregations, solidification cracking, and heat affected zone (HAZ). The IRG shows the conduction mode of penetration with a high width-to-depth ratio under a bigger beam diameter and top-hat type beam profile. The IRG boundaries have irregular profiles due to the dissolution of interdendrite regions and eutectic phases. The IRG showed fine dendrites and solidification cracks with reduced microsegregation levels. The solidification cracking is mainly attributed to thermal stresses and the microcracking in HAZ is attributed to the dissolution of low melting Mo and Ti eutectics. The evolved HAZ ranges from 15% to 20% of the IRG depth. The LISD volume is evaluated as IRG plus HAZ for removal by machining process.