Influence of Ta on the fracture toughness of arc evaporated Ti-Al-N

With in-situ micromechanical cantilever bending tests, we show that the fracture toughness (K-IC) of Ti-Al-N coatings can be increased through Ta-addition. The Ti0.54Al0.46N, Ti0.49Al0.44Ta0.07N, Ti0.44Al0.41Ta0.15N, and Ti0.38Al0.34Ta0.28N coatings investigated, exhibit K-IC values of 3.5 +/- 0.3, 3.2 +/- 0.1, 4.7 +/- 0.2, and 3.3 +/- 0.1 Mpa root m, respectively. Thus, the highest K-IC value is obtained for the coating with 15 at% Ta at the metal sublattice, which also exhibits the highest hardness, 35 +/- 1 GPa. The experimentally found trends are in good agreement with ab initio calculations predicting an increase in ductility and cohesive strength with increasing Ta-content for single phase face-centred cubic (stoichiometric) compounds. High Ta containing coatings tend to form additional phases with higher nitrogen contents and possess lower K-IC values than predicted. (C) 2018 Elsevier Ltd. All rights reserved.