Surface integrity of laser-assisted turning of the GH4169 alloy

Abstract

The unique properties of GH4169, such as low thermal conductivity, high strength at high temperatures, and work hardening characteristics, make it difficult to machine. As an effective way to improve the machinability of materials, laser-assisted machining (LAM) has the advantages of reducing the cutting force, restraining chatter, improving productivity, and prolonging tool life. This study investigates the surface integrity of GH4169 in LAM, including the surface roughness, surface defects, microhardness, residual stress, and white-layer formation. First, the depth of the heat-affected layer from 380 to 760 r/min was determined to ascertain the depth of cutting. Secondly, at different cutting parameters, the surface roughness was found to be significantly reduced. LAM leads to a more severe plastic deformation, producing a thicker hardened layer and higher surface hardness on the fabricated substrate, but its internal hardness is less than that of samples made by conventional machining (CM), owing to thermal softening. Both machining methods produce residual tensile stresses, which are larger in LAM. Thirdly, the results of a surface integrity experiment show that white-layer generation is a consequence of the combination of phase change, heat, and plastic deformation. Finally, a comprehensive fuzzy evaluation considering the surface roughness, surface defects, microhardness, residual stress, and thickness of the white layer is established, which verifies that LAM significantly improves the surface integrity of GH4169, setting up a theoretical foundation and technical reference for the laser-assisted turning of nickel-based superalloys.