Structure, mechanical and thermal properties of CrAlBSiN coatings prepared by cathodic arc evaporation

In this work, the effect of B and Si addition on the microstructure, mechanical properties, thermal stability and oxidation resistance of CrAlN coating was studied. Cr0.42Al0.58N, Cr0.37Al0.59B0.02Si0.02N, and Cr0.35Al0.58B0.03Si0.04N coatings were prepared by cathode arc evaporation. The three coatings all reveal single-phase cubic structure. The hardness of Cr0.37Al0.59B0.02Si0.02N coating increases to 32.5 ± 1.1 GPa compared with Cr0.42Al0.58N (30.2 ± 0.7 GPa) due to solid solution strengthening. However, the thickened grain boundary due to the segregation of excess B and Si in Cr0.35Al0.58B0.03Si0.04N slightly reduces the hardness to 31.6 ± 0.7 GPa. The addition of B and Si by 2 at.% retards the precipitation of w-AlN and the dissociation of CrN bonds of CrAlN coating upon annealing. However, the increase of B and Si contents makes no difference to the formation temperature of h-Cr2N, but promotes the formation of w-AlN during annealing. The addition B and Si endows both CrAlBSiN coatings with higher hardness after annealing in comparison with Cr0.42Al0.58N. After oxidation at 1100 °C for 15 h, Cr0.42Al0.58N, Cr0.37Al0.59B0.02Si0.02N, and Cr0.35Al0.58B0.03Si0.04N coatings show oxide layers with thicknesses of ∼2.8, ∼1.0 and ∼1.2 μm, respectively. Among the three coatings, Cr0.37Al0.59B0.02Si0.02N coating reveals the best overall performance.