Dry turning performance of TiN–WSx/TiN hard-lubricious bilayer composite coating

Dry machining is receiving immense attention worldwide to eliminate or minimize the harmful environmental effects of cutting fluids. The present work investigates dry machining performance of a bilayer coating with top-layer of hard-lubricious TiN–WSx, supported by a hard TiN under layer. During dry turning of AISI 1060 steel, the bilayer coated carbide tool registered significantly less cutting forces as compared to its TiN coated counterpart in the cutting velocity range of 77–230 m/min. In prolonged turning test at cutting velocity of 200 m/min, it also exhibited notably higher tool life on the order of 13 and 2.17 times respectively as compared to the uncoated WC and monolayer TiN coated tool. Such improved performance of bilayer coating was found to be associated with its microstructure, mechanical and tribological properties. Existence of lubricious WS2 phase in the composite TiN–WSx layer along with superior coating adhesion and equivalent nanohardness as compared to TiN resulted in low cutting forces. Formation of W–O tribo layer on surface of worn-out coating on flank surface of tool aided in improving tool life during prolonged turning test.