Rolling contact behavior of PVD Ti/TiN coated austempered ductile iron

D. COLOMBO; M. ECHEVERRÍA; J. MASSONE; A. MARQUEZ

Congreso; SBPMat 2014; 2014

Sociedad Brasileira de Pesquisa de Materiales

Austempered ductile iron (ADI) is increasingly being used for the manufacturingof mechanical components subjected to rolling contact fatigue (RCF), such asgears and cams. Several authors studied the RCF behavior of ADI with differentnodule counts and austempering temperatures. They found that ADIresistance to RCF increases as austempering temperature decreases and nodulecount increases. Graphite nodules act as preferential sites for crack nucleation.Consequently, the use of surface treatments could offset the negative effect of thenodules.The authors of the present work studied the rolling contact fatigue (RCF)behavior of PVD CrN and TiN coated ADI. It was found that the RCFresistance of coated samples is lower than that of uncoated samples. Failures incoated samples are mainly characterized by coating delamination. Graphitenodules present on the substrate surface act as preferential sites for coatingfracture and subsequent delamination due to the large properties difference withrespect to coatings. Consequently, the application of multilayer coatings couldenhance ADI resistance to RCF by modifying the properties gradient betweensubstrate and coating.On this basis, the aim of this work is to study the RCF behavior of ADI samplescoated with Ti/TiN by a cathodic arc. The effect of the Ti interlayer thickness onthe RCF life is also evaluated. Coatings were applied in an experimental reactorusing processing parameters specifically selected for ADI. RCF tests wereperformed in a flat washer type testing rig, using a thrust ball bearing as acounterpart. The maximum contact pressure was set at 1400 MPa. RCF testsresults were analyzed using the two-parameter Weibull distribution.