Compressive stress, preferred orientation and film composition in Ti-based coatings developed by plasma immersion ion implantation-assisted deposition

Plasma immersion ion implantation-assisted deposition has been employed to develop Ti-based coatings in the presence of reactive nitrogen environment. When TiN coatings have been developed on Al alloys, it has been observed that a large compressive stress develops in the coating, which can be reduced when the substrate bias is increased. The formation of stress is attributed to atomic peening effect that densifies a coating, whereas thermal spikes generated at high substrate bias reduce the stress. For TiAl coatings delivered from an alloy plasma source, the Al content decreases with increasing negative substrate bias. This is in agreement with the results of TRIDYN ballistic computer simulations, which confirm that the film composition is significantly influenced by preferential sputtering. The results indicate that time-averaged substrate bias is an ill-defined parameter to describe coating properties deposited by the above technique.