Numerical analysis of the effect of coating microstructure on three-dimensional crack propagation in the coating under rolling contact fatique conditions

Hard protective coatings produced by the physical vapor deposition (PVD) processes can potentially be used to prevent rolling contact fatigue (RCF) failures in gears and rolling bearings. Although TiN appears to be an attractive material for such applications, the RCF performance of PVD TiN coatings is limited by their columnar microstructure. One possible solution is to use interlayers interrupting the column growth in TiN to achieve a more equiaxed grain morphology. In this paper, the effect of the coating layer structure on the propagation of a three-dimensional crack through the coating thickness is studied theoretically. Numerical simulations of both planar and kinked three-dimensional cracks under cyclic contact loading are performed using a new numerical approach recently developed by the authors, which is based on a combination of the fast Fourier transform (FFT) technique, the eigenstrain theory, and the conjugate gradient method. The simulation results indicate that high-endurance TiN-based coatings can in principle be produced by alternating relatively thick TiN layers with much thinner interlayers made of another material.