Development and testing of multilayer physically vapour deposited coatings for piston rings

Abstract The development of multilayer coatings prepared by physical vapour deposition (PVD) for piston rings of internal combustion engines to decrease the wear of both ring and cylinder is discussed. Theoretical considerations on the wear and composition of the PVD coatings for piston rings are presented. An optimization of the combination, thickness and deposition conditions of the coating layers is proposed. It was found that the coating must have layers for different purposes: running in, wear resistance, compliance, adhesion. Wear tests of piston pairs with cast iron rings having ion-assisted arc-evaporated PVD coatings consisting of TiN and titanium layers and chromium-electroplated coatings and of piston pairs without coatings were carried out. Application of the developed PVD coating resulted in a ring wear of 30% compared with uncoated rings and 60% compared with rings having chromium-electroplated coatings, the wear of cylinders against coated rings being 70% compared with the wear against uncoated rings. A conclusion concerning the advantage of replacing chromium-electroplated coatings with multilayer PVD coatings is drawn.