Influence of A1N layers on mechanical properties and thermal stability of Cr-based nitride coatings

摘要

Based on their excellent thermal stability and mechanical properties ceramic-like hard coatings are highly valued for various industrial applications. Here we study the effect of additional A1N layers (3 or 10 nm thin) on the mechanical and thermal properties of cubic CrN, Cr_(0.4)Al_(0.6)N and Cr_(0.37)Al_(0.6)Y_(0.03)N. To focus our research on the influence of the additional layers, but minimizing the influence of the additional phase, we kept the overall AIN-layer content at a minimum (<14%). The hardness of the cubic Cr-based nitride layers is not influenced by the addition of coherently grown 3 nm thin A1N layers, due to their small overall content. The formation of wurtzite A1N, for the -10 nm thin layers, breaks the coherency to the cubic Cr-based nitride layers. Thereby re-nudeation is promoted, resulting in a smaller grain size and consequently an actual hardness increase of about 3 GPa for CrN/AIN, Cr_(0.4)Al_(0.6)N/AlN and Cr_(0.37)Al_(0.6)Y_(0.03)N/AlN coatings, respectively, when compared to the monolithically grown cubic Cr-based nitrides or the multilayers containing c-AlN. Both multilayer types, with 3 and 10 nm thin A1N layers, exhibit a similar dependence of their hardness on the annealing temperature. The hardness maximum of 36 GPa was obtained for the Cr_(0.37)Al_(0.6)Y_(0.03)N/AlN multilayers after annealing at 900 °C. This study clearly demonstrates that even a small addition of thin A1N layers to CrN and Cr_(0.37)Al_(0.6)Y_(0.03)N nitride layers increases their mechanical response to annealing treatments.