Tribological and Machining Performance of Graphite-, CaF₂- and MoS₂-Coated Mechanical Micro-textured Self-lubricating Cutting Tool

Abstract

In recent years, micro-textured cutting tools have shown great potential to eliminate the use of cutting fluids and move towards dry machining at least for limited applications. Even then, at higher load, severe friction exists at dry sliding contacts, resulting in large amount of heat generation, high temperature and wear. There is a vast scope to further enhance the tribological performance of micro-textured surfaces during dry sliding contact for heavy load applications. One such way is to coat the micro-textured surface with solid lubricants. In this work, mechanical micro-textures were fabricated on the surface of the high-speed steel (HSS) pins using the scratch tester. Mechanical micro-textured HSS pins were coated with graphite, calcium fluoride (CaF₂) and molybdenum disulphide (MoS₂). Tribological performance of untextured, uncoated mechanical micro-textured and solid lubricant (graphite, CaF₂ and MoS₂)-coated mechanical micro-textured HSS pins were investigated using pin-on-disc tribometer in terms of wear, coefficient of friction, weight loss and wear coefficient of pins. Afterwards, worn-out surfaces of pins were observed under field-emission scanning electron microscope, optical microscope, non-contact surface profilometer and energy-dispersive spectroscopy to understand the wear mechanism as well as the elemental composition of the sliding surface. Machining performance was also compared with untextured, uncoated textured and solid lubricant (graphite, CaF₂ and MoS₂)-coated mechanical micro-textured HSS cutting tools. The results show that MoS₂-coated mechanical micro-textured HSS pins and cutting tools provided the best tribological and machining performance among all.