Fatigue properties of a 316L stainless steel coated with different TiNx deposits

The effect of different TiNx deposits, specifically TiN0.55, TiN0.65 and TiN0.75, on the fatigue properties of a 316L stainless steel has been investigated. Such films were of approximately 3 μm in thickness and were deposited industrially by means of closed field unbalanced magnetron sputtering (PVD). It has been determined that the application of such coatings to the steel substrate gives rise to a significant increase in both the yield strength and the fatigue properties of the composite material, in comparison with the uncoated steel. The increase in fatigue life has been quantified in terms of the computed values of the Basquin parameters of the different materials tested. Thus, it has been shown that, depending on the composition of the film, the fatigue life of the steel can be increased between 566 and 1677% and the fatigue limit can also be increased between 9.1 and 10.8%. From the microscopic point of view, it has been observed that the film remains well adhered to the substrate either during tensile or fatigue testing. Also, it has been determined that the fatigue fracture of the substrate–coating composite is dominated by the fracture of the TiNx film since fatigue cracks have been observed to form first within it and subsequently to propagate towards the substrate. It has been concluded that the increase in fatigue properties of the coated substrate is associated with the intrinsic higher mechanical properties of the deposits with respect to those of the substrate and to the apparent good adhesion of the deposits.