Effects of Machining Parameters on Surface Integrity when Turning Inconel 718

When cutting nickel-based alloys, the machining parameters significantly influence the surface integrity. This paper describes face-turning experiments using the nickel-based alloy Inconel 718 with two types of inserts. The effects of various turning parameters on the surface roughness, residual stress, microhardness, and microstructure of the alloy samples are investigated for both ceramic and carbide inserts. A quadratic surface roughness response model incorporating the cutting speed, cutting depth, and feed rate is developed, and the micromechanics and microstructure in the turned subsurface are analyzed under three levels of cutting parameters. The results show that a smoother, more uniform surface is obtained when using a ceramic insert. The residual stress and microhardness distributions induced by the carbide and ceramic inserts are similar. The residual stress layer is about 80 µm thick and the work-hardened layer has a thickness of around 70 µm. No severe plastic deformation is observed with either the carbide or ceramic insert. Generally, the ceramic insert is more suitable for turning Inconel 718 than the carbide insert. A low cutting speed, moderate cutting depth, and moderate feed rate are found to produce excellent surface integrity characteristics.