Microstructural impact of carbide substrates on machining performance and wear behavior of HiPIMS TiAlSiN–coated micro-drills on SS316 steel

TiAlSiN–coated tools are recommended for machining gummy and strain-hardenable austenitic stainless steels for their superior wear resistance and thermal stability. However, sustenance of such coatings is reportedly more challenging on micro-tools due to the complex material removal mechanics in micro-drilling. The current study attempts to investigate the impact of carbide substrate microstructure on the sustenance of this coating on micro-drills when deposited by high power impulse magnetron sputtering (HiPIMS) and explore its subsequent influence on the tool’s performance in machining of SS316 steel, comparing with uncoated counterparts. It was assessed by thrust force (Fz), torque, acoustic emission (AE) signals, micro-hole quality, and micro-tool condition. Carbide tools with finer carbide grain exhibited unimodal distribution, resulting in higher hardness. They consistently outperformed those with coarser carbide grains in multimodal distributions with lower hardness. Coated tools were expectedly superior to uncoated ones, but coatings experienced earlier and more severe delamination on substrates having softer and more heterogeneous microstructure. Machining results indicated a 40% reduction in peak Fz, 33% reduction in torque, and 20% reduction in acoustic energy with coated tools having finer grains in unimodal distribution. Higher substrate hardness and superior microstructural homogeneity played a key role in the enhanced performance of coated micro-tools.