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Coating systems provide protection to tribological components such as bearings that experience heavy contact loads from wear. In this study, hard coating-ductile substrate systems were characterized by experiments and computational models.Tensile cracking experiments were carried out on tungsten carbide/diamond like carbon composite coatings on stainless steel substrates. Acoustic emission technique was used to monitor cracks in the coating. The fracture strain of the coating and the intercrack spacing were quantified in addition to strain corresponding to crack saturation. A 2-dimensional finite element model using cohesive zone elements was developed to predict cracking in thin film coating – interlayer – substrate systems that are subjected to tensile loading. The constitutive models were chosen to represent a metal carbide/diamond like carbon composite coating with a titanium interlayer and a steel substrate. Material properties of the coating and interlayer along with the cohesive finite element parameters were varied to study effects on stress distributions and coating cracking. Stress distributions were highly non-uniform through the coating thickness. Thus the initiation and arrest of tensile cracks differed from what is predicted by simple shear-lag theory. Inter-crack spacing distributions resulting from the variation of different parameters were quantified and compared with those from experiments. Multilayer coatings with alternate hard and soft layers play increasingly important role because of the seemingly better performance in tribological and wear applications over monolithic coatings. However, the role of overall thickness, number of layers, and individual layer thickness cannot be overlooked and need to be optimized to minimize damage in the multilayer coatings. 2-dimensional finite element models using cohesive zone elements were developed to predict damage in multilayer coatings subject to spherical indentation. Damage in coatings was characterized as through thickness coating cracks and interfacial delamination. A design of computer experiments (DACE) approach was used to build metamodels in order to predict damage variables for a range of range design space consisting of 2, 4, 6, and 8 layers multilayer coating architecture. |
