Rolling contact fatigue resistance of PAPVD Ti/TiN coated austempered ductile iron

DIEGO A. COLOMBO; MARÍA D. ECHEVERRÍA; JUAN P. QUINTANA; JUAN M. MASSONE; ADRIANA B. MÁRQUEZ

Conferencia; PBII&D 2015; 2015

Austempered ductile iron (ADI) is increasingly being used for the manufacturing of mechanical components subjected to rolling contact fatigue (RCF), such as gears and cams. Several authors studied the RCF behavior of ADI with different nodule counts and austempering temperatures [1, 2]. They found that ADI resistance to RCF increases as austempering temperature decreases and nodule count increases. Graphite nodules act as preferential sites for crack nucleation. Consequently, the use of surface treatments could offset the negative effect of the nodules.The authors of the present work studied the rolling contact fatigue (RCF) behavior of PVD CrN and TiN coated ADI [3]. The coating thickness was close to 2.5 µm. It was found that the RCF resistance of coated samples is lower than that of uncoated samples. Failures in coated samples are mainly characterized by coating delamination. Graphite nodules present on the substrate surface act as preferential sites for coating fracture and subsequent delamination due to the large properties difference with respect to coatings. Consequently, the application of multilayer coatings could enhance ADI resistance to RCF by modifying the properties gradient between substrate and coating.On this basis, the aim of this work is to study the RCF behavior of ADI samples PAPVD coated with Ti/TiN. The effect of the TiN layer thickness on the RCF life is also evaluated. Coatings were applied by cathodic arc deposition (CAD) in an experimental reactor using processing parameters specifically selected for ADI. Deposition times were adjusted to obtain a Ti interlayer thickness of about 0.3 µm and different TiN layer thicknesses. RCF tests were performed in a flat washer type testing rig, using a thrust ball bearing as a counterpart. The maximum contact pressure was set at 1400 MPa. RCF tests results were analyzed using the two-parameter Weibull distribution. The rolling track of the tested samples was examined by using SEM.