Characterization of the frictional properties of various coatings at the tool/chip/workpiece interfaces in dry machining of AISI 4140 steel

This work deals with the development of a new tribometer designed for the characterization of the frictional properties at the tool—chip—workpiece interfaces in cutting processes. The average contact pressure can be selected up to 3 GPa under sliding velocities reaching 300 m/min. Moreover, the system provides a continuously regenerated contact surface. Under such severe conditions, which are not reachable with conventional tribometers, the apparent friction coefficient is quantified in parallel to the heat flux transmitted to the pin. This new system has been applied to the characterization of the frictional properties during the dry machining of a AISI 4140 treated steel with various coated carbide substrates. The coatings investigated in this work are: TiN, TiAlN, AlCrN coatings deposited by physical vapour deposition (PVD). A wide range of sliding velocities and pressures have been investigated in dry conditions. It has been shown that the coating is the most influential parameter, followed by the sliding velocity, and finally the pressure. As far as the friction coefficient is concerned, the superiority of AlCrN and TiAlN coatings in dry cutting has been revealed.