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

Abstract

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 (Λ) of 41 and 25 nm, and the two Ti0.55Al0.45N/Ta0.77Al0.23N multilayers have Λ = 42 and 26 nm, respectively. These are compared with Ti0.51Al0.43Ta0.06N/Ta0.77Al0.23N multilayers having Λ ~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 ~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 ε-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 Λ = 13 nm, whereas the Ti0.55Al0.45N/Ta0.77Al0.23N multilayer with Λ = 42 exhibits the lowest hardness (31.1 ± 2.1 GPa) combined with a high indentation modulus (392 ± 25 GPa).