Residual stress and its effect on failure in a DLC coating on a steel substrate with rough surfaces

• Significant effects of rough surfaces on the residual stress and substrate plasticity.
• Interfacial failure is more sensitive to the shear traction delamination.
• Remarkable increase of strain energy release rate in multi-crack model.
• Interlayer Ti can enhance the durability of coating–substrate system.

A finite element model is proposed to simulate the residual stresses (thermal and intrinsic stresses) of a system consisting of a DLC coating on a steel substrate with rough surfaces. The risk of failure of residually stressed coating–substrate systems is evaluated by using the cohesive zone model, extended finite element method, and J-integral theory. It is found that relatively large residual stresses as well as coating cracks are normally generated near the convex asperities of the interface, and the steel plasticity is concentrated around the concave asperity of the substrate surface near the edge. Moreover, driving forces and evolutions of failures in the coating–substrate system are presented. One can see that the interfacial failure is more sensitive to the shear traction delamination than to the normal one. For the issue of multi-crack, two closely spaced crack tips are vulnerable to coalesce during the propagation process. Additionally, in the light of mechanics, it is demonstrated that the interlayer Ti is effective in failure protection for the entire system. Numerical results have also been compared with other computational or experimental works, and can establish a theoretical basis for enhancing the durability of PVD coating–substrate systems.

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