Improved mechanical and thermal properties of CrAlN coatings by Si solid solution

Incorporation of a fourth constituent into CrAlN coating to optimize its properties attracts great attention. Here, the effect of Si on the structure and properties of CrAlN coating is investigated. The solid solution of Si into CrAlN coatings promotes the w-AlN growth, and thus results in a structural transition from Cr0.48Al0.52N with single phase cubic structure to Cr0.42Al0.49Si0.09N and Cr0.37Al0.54Si0.09N with mixed cubic-wurtzite structure. An increase in hardness from ∼25.6 GPa for Cr0.48Al0.52N-∼34.4 GPa for Cr0.42Al0.49Si0.09N and ∼32.7 GPa for Cr0.37Al0.54Si0.09N is obtained due to the solution hardening and grain refinement. Annealing of Cr0.48Al0.52N leads to c-Cr formation via h-Cr2N under N2 releases as well as w-AlN precipitation. Alloying with Si retards the w-AlN precipitation and N-loss, where the final precipitation phases after annealing of the Si-containing coatings are w-AlN, c-Cr3Si and c-Cr, respectively. Furthermore, the oxidation resistance of CrAlN coating is also improved by Si-addition.