On the microstructure and property development of d.c. magnetron co-sputtered ternary titanium aluminium nitride coatings: effect of nitrogen deposition pressure

Abstract

Advanced ternary (Ti,Al)N coatings were produced by reactive magnetron co-sputtering with a 300 magnetron configuration. The results reflected the significance and complexity of the nitrogen pressure effect on the coating development. As the nitrogen pressure increased above 0.4 mTorr, a transition of the coating structure from densified, fine columnar grains to porous faceted grains occurred, resulting in an abrupt decrease of the coating hardness. It is believed that an increase of the nitrogen pressure to high values may cause serious collision and scattering of the depositing atoms and poisoning of the targets, thus resulting in significantly fewer atoms/molecules arriving at the substrate with much lower energies. The adatom mobility and the nucleation rate in the coatings are therefore greatly reduced, resulting in development of a coarse grained structure.