Influence of niobium addition on microstructure, mechanical properties and oxidation resistance of ZrN coatings

In this study, Zr-Nb-N coatings with 0-3.8 at.% Nb addition were deposited by magnetron co-sputtering deposition. The results reveal that Nb atoms substitute Zr atoms in Zr-N lattice, forming the solid solution structure. All the Zr-Nb-N coatings illustrate a dense columnar structure with the preferred orientation of (200), showing independent of Nb addition. Nanoindentation result reveals a promoted hardness of the Zr-Nb-N coatings from 23.9 +/- 0.7 GPa to 28.4 +/- 0.5 GPa with enhanced Nb content from 0 to 2.8 at.% due to both the solid solution strengthening and Hall-Petch effect. Scratch tests show that adhesion between substrates and coatings can be improved by Nb addition. After oxidation in air at 600 degrees C for 2 h, microstructural studies indicate the oxide scales consist of monoclinic-ZrO2 outer layer and tetragonal-ZrO2 inner layer. Moreover, ZrO2 can be stabilized in the tetragonal phase by Nb doping. The Zr-Nb-N coating with 1.3 at.% Nb addition exhibits superior oxidation resistance, while excess Nb addition produces detrimental effects on oxidation resistance. (C) 2014 Elsevier B. V. All rights reserved.