Orientation dependent tribological behavior of TiN coatings

The preferred growth direction of cathodic arc physical vapor deposition-produced TiN coatings changes from (1 1 1) to (2 2 0) with high voltage pulsed bias application in the presence of Ar gas. In this study, tribological properties of these coatings were investigated via reciprocating wear tests against an inert counterbody for observing the role of orientation on tribological properties. Friction coefficients and wear of (2 2 0) oriented coatings were observed to be significantly lower compared to (1 1 1) oriented coatings. Micro-Raman investigations of the wear debris formed during tribotest revealed clear differences between (1 1 1) and (2 2 0) oriented films. Wear debris obtained from (2 2 0) oriented coatings consisted of nc TiO2 phases (anatase and rutile) whereas (1 1 1) oriented coatings produced amorphous Ti oxides. This behavior is attributed to the orientation dependent oxidation kinetics of the coatings as verified with isothermal oxidation tests. A mechanism for improved tribological behavior is proposed based on the obtained results.