Multiple cracking in CrN and Cr2N films on brass

Multiple cracking in brittle CrN and Cr2N films on a brass substrate is examined by a combination of experimental observations and finite-element modeling with the goal of better understanding the mechanics of film cracking. Films of thickness 1-6 μm, deposited by unbalanced magnetron sputtering onto brass, are fractured by uniaxially straining the brass in tension. In situ observation in the optical and scanning electron microscope provide accurate measurements of the film crack spacing as a function of strain. Finite-element modeling was conducted to show that a substantial in-plane stress gradient through the film thickness exists during the development of cracks, and that this gradient likely affects the saturation crack spacing. It is further shown through the experimental observations and associated modeling that the stress redistribution in the substrate during film cracking and the resulting stress transfer to the film affects the mechanism of cracking.