Optimizing Hole Shape and Improving Surface Quality of Inconel 718 Alloy by High-Temperature Chemical Assisted Laser Processing

High-quality micro-hole processing of superalloy has always been challenging work in the aerospace and automobile industries. A novel high-temperature chemical assisted laser processing technology was investigated to provide an one-step in-situ method for eliminating defect layer and optimizing hole shape, thereby solving the two challenges of surface roughness and taper in micro-hole processing. An environmental-friendly chemical liquid was adopted. Chemical etching occurred at the interface of the material-modified layer in the local high-temperature environment to minimize surface roughness, and the chemical liquid played a role of a confinement layer, limiting the expansion of the high-temperature gas and plasma leading to the laser plasma ablation pressure applied to the substrate material. The influences of defocus and laser pulse interval on hole formation and geometry characteristics, taper angle, and surface roughness were investigated. The experiment results revealed that when the laser pulse interval was less than or equal to 0.1 ms, the blind hole shape was close to being cylindrical, when the laser pulse interval was 1 ms, the blind hole was a conical shape with a deeper depth. The interaction mechanism in high-temperature chemical assisted laser drilling was analyzed, including laser plasma ablation pressure, and liquid jet following cavitation bubble collapse in the liquid confined region. This study has a potential application in the field of super-alloy drilling.