Rolling contact fatigue behavior of TiN based coatings deposited on ADI by cathodic arc deposition and plasma based ion implantation and deposition

This work studies the surface characteristics and, particularly, the rolling contact fatigue (RCF) behavior of austempered ductile iron (ADI) samples coated with TiN based coatings of about 1 mu m in thickness. Films synthesized by cathodic arc deposition (CAD) at a fixed nitrogen flow, compositional gradient films synthesized by CAD at a variable nitrogen flow and plasma based ion implanted and deposited (PBIID) films were comparatively analyzed. The results indicated that CAD films showed a strong TiN (111) preferred orientation while PBIID films a more randomly orientation. The crystallite size of CAD films was more than the double of PBIID films. Residual stresses of the PBIID films were lower than those of CAD films, the lowest hardness and elastic modulus were obtained for CAD films grown at variable nitrogen flow, while no significant differences in roughness, H/E ratio and adhesion were observed among the different films. Regarding RCF tests, failures in samples coated with TiN at constant flow were characterized by a progressive coating delamination followed by the formation of fatigue spalls inside the delaminated areas. Failures in samples coated with PBIID and gradient TiN were characterized by the formation of fatigue spalls with slight coating delamination. There were no significant differences between the RCF resistance of uncoated ADI and the samples with CAD films while the samples with PBIID films had a noticeably higher resistance. The better performance could be associated with the low compressive residual stresses and the fine grained microstructure induced by the PBIID process.