Nondestructive separation of residual stress and composition gradients in thin films by angle- and energy-dispersive X-ray diffraction. II. Experimental validation

The different approaches for separating residual stress and composition gradients introduced in the first part of this series [Klaus & Genzel (2017). J. Appl. Cryst. 50, 252–264] are demonstrated with the experimental example of a graded Ti(C,N) coating layer deposited by a modified high-temperature chemical vapour deposition process on a cemented carbide substrate. The coating layer features a depth gradient in the lattice parameter in the strain-free direction of the biaxial stress state, ψ^*,hkl, and tensile residual stresses σ_|| which are nearly uniform over the coating thickness but drop down significantly towards the free surface. On the assumption that the out-of-plane stress component σ₃₃ can be neglected, the gradient is related to the variation in the chemical composition with depth. Therefore, the example considered here corresponds to case (d) of possible combinations of residual stress and composition gradients discussed in the first part of this series. The comparison of the results achieved by means of the different methods reveals the importance of choosing appropriate experimental conditions that fit best to the sample to be investigated. For the case of thin-film analysis, it is shown that the X-ray information depth is the crucial parameter which should match the film thickness.