Evaluation of adhesive damage in a nitrided stainless steel under cyclic contact loading

In this study, adhesive damage in a nitrided AISI 316L stainless steel is evaluated by cyclic contact loading. The AISI 316L steel was hardened by the salt bath nitriding process at a constant temperature (580 °C) and three different exposure times (1 h, 3 h and 5 h). Mechanical properties such as Young's modulus (E) and hardness (H) were obtained by nanoindentation testing, where the H3/E2 ratio was used as an indicator of the fracture resistance of the nitride layers. Cyclic contact loads were applied to the nitrided steels using a spherical indenter of 3 mm in diameter. The layer/substrate systems were evaluated under 50,000 load cycles and a constant frequency of 5 Hz. Adhesive damage was observed at the interface between the compound-layer and the diffusion zone, where the samples with a thicker nitride layer showed more severe damage. In addition, the finite element method was used to obtain the stress field in the nitrided AISI 316L steel caused by cyclic contact loading, where both the maximum principal stress and the maximum shear stress were related to the adhesive damage observed in the experimental test.