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

Abstract 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 Ti 0·54 Al 0·46 N, Ti 0·49 Al 0·44 Ta 0·07 N, Ti 0·44 Al 0·41 Ta 0·15 N, and Ti 0·38 Al 0·34 Ta 0·28 N coatings investigated, exhibit K IC values of 3.5 ± 0.3, 3.2 ± 0.1, 4.7 ± 0.2, and 3.3 ± 0.1 M P a 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.