Wear behavior of bilayer Ti/TiN coatings on ADI

J. P. QUINTANA; M. ECHEVERRÍA; J. MASSONE; MARQUEZ, A; D. COLOMBO

Congreso; Plasma based ion implantation and deposition 2017; 2017

Austempered ductile iron (ADI) is commonly used for the manufacturing of mechanical components subjected to rolling or rolling/sliding contacts, such as gears and cams. A major cause of failure in this type of components is rolling contact fatigue (RCF). Hard coatings are widely used to improve hardness, wear resistance and corrosion resistance of a variety of metals, including ADI [1, 2]. In previous works, ADI samples coated with hard coatings deposited by cathodic arc deposition (CAD) showed that their RCF resistance increased as coating hardness and film thickness decreased [3, 4]. In addition, it was observed that graphite nodules present on the substrate surface act as preferential sites for coating delamination due to large mismatch in mechanical properties between coatings and graphite nodules. This sharp interface could be eliminated by introducing the concept of functionally gradient materials (FGM) in the design of the coating [5]. Plasma based ion implantation and deposition (PBII&D) could be another alternative to improve the RCF behavior of coated ADI. Materials and Methods: High resistance ADI samples were prepared following conventional practices of melting, casting, heat treatment and machining. Three types of Ti/TiN films were synthesized using a DC cathodic arc system: compositional gradient (GC) films by gradually varying the nitrogen flow during deposition with the sample at floating potential, constant composition (CC) films by using a constant nitrogen flow with the sample at floating potential and (PBIID) films at a constant nitrogen flow using high voltages pulses for biasing the substrates. Film thickness, microstructure, surface roughness, mechanical properties, residual stresses and adhesion of each coating variant were determined. RCF tests were performed in a flat washer type testing rig using lubricated, pure rolling conditions. The maximum contact pressure (p0) was set at 1400 MPa. The rolling track of the samples was examined by SEM and EDS. RCF results were analyzed using the two-parameter Weibull distribution.