Performance evaluation of nano-composite ceramic-coated high-speed steel (HSS) drills in high-speed machining

The present work evaluates and quantifies the effect of superhard nano-composite ceramic coatings (nc-AlTiN/a-Si3N4) for high-speed drilling of AISI 316L steel. Different thicknesses (2.5, 3, 3.5, and 4 μm) of this novel coating are deposited on commercially available TiN-coated HSS drills via PVD (physical vapor deposition). Performances are evaluated in terms of tool wear aspects, workpiece temperature rise, surface roughness, and hole dimensional accuracy in high-speed regime using constant machining parameters (cutting speed of 150 m/min and feed rate of 0.1 mm/rev at 4000 rpm). It is found that coating thickness has positive effect on performance measures considered; however, dimensional accuracies improve logarithmically suggesting diminishing returns beyond a particular value. For surface roughness, maximum improvement was seen for 4-μm coating thickness wherein mean improvement was ~ 34% w.r.t. baseline (TiN). Also, 4-μm-thick nc-AlTiN/a-Si3N4-coated tool outperformed the baseline tool by orders of magnitude in terms of flank wear. Flank wear and deformation of the chisel edge are the primary wear modes for TiN-coated tool; however, for all ceramic-coated tools, chipping is dominant failure type.