Adhesion tendency of PVD TiAlN coatings at elevated temperatures during reciprocating sliding against carbon steel

Abstract

This work focussed on assessing the contact conditions driving the adhesion tendency of PVD TiAlN coated cemented carbide during reciprocating sliding against a normalized AISI 4137 carbon steel. A special emphasis is given to the surface topography of the coating. Results are analysed in terms of friction and material transfer over a large range of temperatures (up to 800°C) and contact pressures. The post-test surface analysis of the specimens is conducted in order to understand the tribological behaviour and elucidate the formation mechanisms of transfer layers. A numerical model is developed to assess the amount of heat effectively transmitted into the first bodies and the temperature of the surfaces in contact.Whereas temperatures close to 400°C ensure the formation of a stable tribofilm reducing friction, the highest temperatures lead to unstable frictional behaviour. Coating surface topography has been seen to be a major parameter driving material transfer during the first stages of the contact and the formation of a transfer layer. Thin and homogeneous layers are almost instantaneously formed with a polished surface whereas some time is required with a rougher one to form a film. A large amount of the frictional power is dissipated into these layers and high temperatures can be reached at the surface due to frictional heating. Contact pressure is found to be a parameter promoting transfer and oxidation.