Structure and mechanical properties of architecturally designed Ti-Al-N and Ti-Al-Ta-N-based multilayers

Four Ti-Al-N/Ta-Al-N multilayer coatings were developed by a hybrid process combining arc evaporated Ti0.55Al0.45N and sputtered Ta0.57Al0.43N or Ta0.77Al0.23N layers. The two Ti0.55Al0.45N/Ta0.57Al0.43N multilayers have a bilayer period (Lambda) of 41 and 25 nm, and the two Ti0.55Al0.45N/Ta0.77Al0.23N multilayers have Lambda = 42 and 26 nm, respectively. These are compared with Ti0.51Al0.43Ta0.06N/Ta0.77Al0.23N multilayers having Lambda similar to 40, 33, 25, and 13 nm and are composed of arc evaporated Ti0.51Al0.43Ta0.06N and sputtered Ta0.77Al0.23N layers. The smallest bilayer period of similar to 13 nm was realised without mechanical shutters, simply by using the two-fold substrate rotation and target arrangement. The alternating growth of Ta0.57Al0.43N respectively Ta0.77Al0.23N layers with arc evaporated Ti0.55Al0.45N or Ti0.51Al0.43Ta0.06N layers allows for full crystallisation in a single-phase face-centred cubic structure, although monolithically grown, these exhibit additional epsilon-TaN and/or wurtzite AlN-type phases. The mechanical properties of our eight different multilayers indicate a dependence on their bilayer period. Highest hardness (33.6 +/- 1.1 GPa) combined with a low indentation modulus (375 +/- 9 GPa) could be realised by Ti0.51Al0.43Ta0.06N/Ta0.77Al0.23N coatings with Lambda = 13 nm, whereas the Ti0.55Al0.45N/Ta0.77Al0.23N multilayer with Lambda = 42 exhibits the lowest hardness (31.1 +/- 2.1 GPa) combined with a high indentation modulus (392 +/- 25 GPa).