Surface integrity of inconel-718 nickel-base superalloy using controlled and natural contact length tools. Part II: Unlubricated

The surface integrity of inconel-718 nickel-base superalloy was investigated using orthogonal cutting at various cutting speeds, depths of cut and chip-tool contact lengths under unlubricated conditions. The experimental work involved the determination of residual stress, plastic strain and microhardness distribution in the surface region and the examination of the surface and subsurface using scanning electron and optical microscope. The results are interpreted in terms of the variation in shear-plane length and consequently the variation in tool forces with the cutting conditions. The results are compared with similar results obtained under lubricated conditions. It is found that the lubricant is effective at low cutting speeds in reducing the tool forces that led to lower hardness and plastic strain in the surface region. In general, the severity of surface damage in terms of intensity and total area affected was decreased with the application of a lubricant. Both residual stresses and plastic strains decreased and the quality of the machined surface improved with an increase in cutting speed, a decrease in depth of cut and with tools having controlled chip-tool contact lengths.