On the fatigue behavior of an AISI 316L stainless steel coated with a PVD TiN deposit

The effect of a TiN coating on the fatigue properties of an AISI 316L stainless steel has been investigated. The coating was approximately 1.4-mum thick and was deposited by means of filtered cathodic arc deposition. It has been determined that the application of such a coating to the steel substrate gives rise to a significant increase in both fatigue life and fatigue limit, 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 maximum alternating stress applied to the material, the fatigue life of the steel can be increased between 400 and 2119%, whereas the fatigue limit was observed to increase by 22%, that is to say, 60 MPa above the fatigue limit of the uncoated substrate, which in the present work was found to be of approximately 381 MPa. From the microscopic point of view, it has been observed that the coating remains well adhered to the substrate both in tension and during fatigue testing at low maximum alternating stresses (480 MPa). However, during fatigue testing at elevated maximum alternating stresses (510 MPa) the coating was observed to delaminate from the substrate. Also, it has been determined that the fatigue fracture of the substrate-coating composite is dominated by the fracture of the TiN coating since fatigue cracks have been observed to form first at the surface of the coating and subsequently to propagate towards the substrate. It has been concluded that the increase in fatigue properties of the coated substrate is associated mainly with the compressive residual stresses present in the coating and to the good adhesion of the coating to the substrate observed in most of the maximum alternating stress range explored in this work. (C) 2003 Elsevier B.V. All rights reserved.