Plasma arc sprayed coatings are largely developed in Perfect Circle Europe because of the wide range of coating materials which ensure numerous tribological properties. Spraying parameters are of great importance in improving the coating structure and therefore the coating wear, adhesive, cohesive and corrosive resistances. The utilized plasma gas is first studied; designed experiments are then achieved to optimize the all spraying parameters. More than the spraying parameters, the powder formulation has a major influence on the coating tribological properties. Several powders are studied with the aim to reduce the ring-liner system wear. Tests on idealized samples coupled with engine tests help us to characterize the tribological behaviour of some molybdenum based coatings.