Effect of Cutting Speed and Tool Coating on Machined Surface Integrity of Ni-based Super Alloy

Inconel 825 belongs to the family of nickel-based super alloy and is widely used in the chemical and marine industry. Although most of the research work was concentrated on machinability of Inconel 718, no such work on the current grade of Inconel 825 has been reported so far. This grade of Inconel is particularly suitable for the applications requiring improved resistance to corrosion. The current study aims at investigating the effect of cutting speed and chemical vapour deposition (CVD) multilayer coating on machined surface integrity of Inconel 825 during dry turning, with particular emphasis on measurement of sub-surface hardness and white layers. Three regions were distinguished beneath the machined surface viz. (a) white layer, (b) plastic deformation region and (c) bulk material. It was observed that increase in cutting speed increased white layer thickness after machining with both uncoated and coated tools. CVD coated cemented carbide insert resulted in decrease in white layer thickness particularly in the lower range of cutting velocity when compared with that obtained by its uncoated counterpart. Vickers microhardness test clearly revealed the work hardening tendency of Inconel 825 with hardness being maximum in the sub- surface region and it decreased when measurements were gradually taken towards the centre of the workpiece. However, this tendency was found to be reduced with the use of multilayer coated tool.