Comparative experimental study on application feasibiility of MTCVD TiCN-Al2O3-TiOCN multi-layer coated carbide and PVD TiN single layer coated composite ceramic inserts during dry machining of Ti-6Al-4V

Due to high temperature strength (hot strength), excellent corrosion resistance and high strength-to-weight ratio, Ti-6Al-4V alloy is considered as a potential candidate for extensive applications in aerospace and biomedical engineering. But, alloy's low thermal conductivity and extreme chemical affinity (towards tool substrate and coating materials) often cause an aggressive cutting environment with a tremendous rise in cutting zone temperature, premature tool wear, and disappointing surface integrity during conventional machining processes. In order to achieve desired machining yield without opting for any coolant, selection of proper cutting tool (based on their geometry and properties) is indeed vital. Thus, the present work examined the performance of MTCVD-TiCN-Al2O3-TiOCN multi-layer coated carbide and PVD TiN single layer coated composite ceramic (Al2O3/TiCN) tool inserts during dry machining of Ti-6Al-4V. Higher friction coefficient (of the coating system) was revealed for the ceramic tool which caused substantial temperature rise at tool-tip. On the other hand, carbide insert imparted lower cutting force (beyond nu = 80 m/min) than ceramic insert due to its better thermo-chemical stability. Coating peel-off and tool flaking were witnessed for ceramic insert due to its thermal instability at higher cutting speeds; while carbide tool was mainly affected by material adhesion, abrasion, and chip fusion (adhesion of broken chip-fragments over tool surface due to high pressure and temperature). It was experienced that induced cutting heat significantly affected chip morphology under a dry cutting environment. Up to nu = 130 m/min, ceramic tool exhibited lower flank wear than carbide tool.