Machining of Inconel 718 Using Coated WC Tool: Effects of Cutting Speed on Chip Morphology and Mechanisms of Tool Wear

Inconel 718 is a nickel-based superalloy extensively used in aerospace industries for its excellent physical, mechanical and chemical properties. Poor thermal conductivity, high toughness and strong work hardening tendency of this alloy adversely affect its machinability. Inconel 718 is therefore treated as 'difficult to cut' or 'hard to cut'. Conventional machining of Inconel 718 faces various challenges like high cutting forces, evolution of huge cutting temperature and rapid tool wear. As a consequence, surface integrity of the machined part becomes disappointing. Excessive tool wear incurs additional cost of tool replacement. To overcome machining difficulties of this alloy, application of coated tool insert is recommended. To this end, the present work attempts to investigate machining performance of Inconel 718 using coated carbide (cemented carbide) tool with chemical vapour deposition multi-layer coating TiN/TiCN/Al₂O₃/TiN (TN4000) under dry cutting environment. Turning experiments are conducted with varied cutting speeds: 50, 75, 100 and 125 m/min at constant feed rate 0.1 mm/rev and constant depth of cut 0.4 mm. Chip morphology including features of chip cross section, free surface of chip and chip reduction coefficient as affected by cutting speed is studied herein. Abrasion, adhesion, chipping off, coating delamination, built-up edge formation, diffusion, etc. are identified as potential wear mechanisms. In addition to flank wear and crater wear, occurrence of notch wear is also distinctly identified. Surface roughness of the finished work part is found better in case of coated tool than uncoated one. Coated tool corresponds to lesser cutting force magnitude, lower cutting temperature and higher value of chip reduction coefficient than the case of traditional uncoated tool.