Microstructure, mechanical properties and oxidation resistance of (Zr, Hf)Nx coatings by magnetron co-sputtering

This study investigates the influence of Hf addition to the microstructure, mechanical properties and oxidation resistance of ZrN coating. (Zr, Hf)N-x coatings with 0-42 at.% Hf were fabricated by reactive co-sputtering in an Ar-N-2 atmosphere. The solid solution-type (Zr, Hf)N-x coatings exhibit a dense and columnar structure with strong (2 0 0) preferred orientation, independent of Hf content. Abnormal grain growth was observed in the coatings with improved Hf content. The highest recorded hardness is 28.6 +/- 0.6 GPa with 05 at.% Hf addition, whereas further increasing the Hf content up to 42 at.% decreases the hardness. The oxidation results demonstrate that the most beneficial content of Hf to improve the oxidation resistance of the ZrN coating is 1.2 at.%. Reduction in inward diffusion paths for oxygen ions, the increase of stoichiometry and the high thermal stability of HfN have been identified as the primary reasons for the improvements of the oxidation resistance. (C) 2015 Elsevier B.V. All rights reserved.