Role of PVD coating on wear and surface integrity during environment-friendly micro-drilling of Ni-based superalloy

Owing to its capability to significantly mitigate the detrimental effects of flood cooling, minimum quantity lubrication (MQL) has emerged as a potential cooling technique for environment-friendly machining. Although coated cutting tools are widely used in the industry, the role of surface coating on micro tools during mechanical micro-machining is relatively unknown. The current research work seeks to explore the mechanism of physical vapour deposition (PVD)-based TiAlN coating during micro-drilling of a Ni-based superalloy (Incoloy 825). MQL was employed considering potential of tool coating to minimize the usage of cutting fluid. Results indicated increase in edge radius due to coating hindered the performance of coated micro-drill while machining with very low feed (1 μm/rev). This was attributed to ‘size effect’. However, elevation of feed, cutting speed and also machining duration (number of holes drilled) was found to be effective for TiAlN coated micro-drill. Thrust force, oversize error and deformed layer thickness along with hole periphery could be satisfactorily reduced under elevated machining condition. Similarly, improvement in resistance to wear of TiAlN coated micro-drill was evident after drilling 58 number of holes. Overall, a reduction in average flank wear up to 43% was observed for coated micro-drill after 168 number of holes when compared to uncoated micro-drill. Therefore, it is recommended to carefully work out a machining condition conducive for successfully utilizing coated micro-drill in machining of Ni-based superalloy.