Influence of Zr on structure, mechanical and thermal properties of Ti-Al-N

Multinary Ti-Al-N thin films are used for various applications where hard, wear and oxidation resistant materials are needed. Here, we study the effect of Zr addition on structure, mechanical and thermal properties of Ti1-xAlxN based coatings under the guidance of ab initio calculations. The preparation of Ti1-x-zAlxZrzN by magnetron sputtering verifies the suggested cubic (NaCl-type) structure for x below 0.6-0.7 and z <= 0.4. Increasing the Zr content from z = 0 to 0.17, while keeping x at similar to 0.5, results in a hardness increase from similar to 33 to 37 GPa, and a lattice parameter increase from 4.18 to 4.29 angstrom. The latter are in excellent agreement with ab initio data. Alloying with Zr also promotes the formation of cubic domains but retards the formation of stable wurtzite AlN during thermal annealing. This leads to high hardness values of similar to 40 GPa over a broad temperature range of 700-1100 degrees C for Ti0.40Al0.55Zr0.05N. Furthermore, Zr assists the formation of a dense oxide scale. After 20 h exposure in air at 950 degrees C, where Ti0.48Al0.52N is already completely oxidized, only a similar to 1 mu m thin oxide scale is formed on top of the otherwise still intact similar to 2.5 mu m thin film Ti0.40Al0.55Zr0.05N. (C) 2011 Elsevier B.V. All rights reserved.