Comparative evaluation of machinability characteristics of Nimonic C-263 using CVD and PVD coated tools

Machining of Nimonic C-263 has always been a challenging task owing to its hot strength, low thermal conductivity, tendency to work harden and affinity towards tool materials. Although coated tools have been used to overcome some of these challenges, selection of coated tool with appropriate deposition technique is of immense significance. The current study attempts to comparatively evaluate various performance measures in machining of Nimonic C-263 such as surface roughness, cutting force, cutting temperature, chip characteristics, and tool wear with particular emphasis on different modes of tool failure for commercially available inserts with multi-component coating deposited using chemical vapour deposition (CVD) and physical vapour deposition (PVD) techniques. Influence of cutting speed (Vc) and machining duration (t) has also been investigated using both coated tools. The study demonstrated remarkable decrease in surface roughness (74.3%), cutting force (6.3%), temperature (13.4%) and chip reduction coefficient (22%) with PVD coated tool consisting of alternate layers of TiN and TiAlN over its CVD coated counterpart with TiCN/Al2O3 coating in bilayer configuration. Severe plastic deformation and chipping of cutting edge and nose, abrasive nose and flank wear along with formation of built-up-layer (BUL) were identified as possible mechanisms of tool failure. PVD coated tool successfully restricted different modes of tool wear for the entire range of cutting speed. Superior performance can be attributed to the hardness and wear resistance properties, thermal stability due to presence of TiAlN phase and excellent toughness owing to PVD technique and multilayer architecture.