Microstructure and mechanical properties of nano-multilayer structured (AlCrMoTaTi)Nx coatings deposited by closed field unbalanced magnetron sputtering

Abstract

(AlCrMoTaTi)Nx nano-multilayer coatings with different N concentration were deposited by varying the nitrogen flow rate using a closed field unbalanced magnetron sputtering. With the nitrogen flow rate increased from 0 sccm to 16sccm, the phase structure changed from a HCP metal phase to a mixed phase of HCP metal and FCC nitride, and then to a fully FCC nitride phase similar to B1-NaCl at the nitrogen flow rate above 12sccm. The (AlCrMoTaTi)Nx coatings formed nano-multilayer super lattice structure with modulation periods of about 2 nm. The FCC structured (AlCrMoTaTi)Nx coatings exhibited hardness ranging between 32.8 and 35.2 GPa, which was related to their superlattice structure with a small modulation period and the inverse Hall-Petch soften effect due to their small grain sizes. The FCC structured (AlCrMoTaTi)Nx coatings also exhibit higher H/E* ratios above 0.09 than that of monolayer binary, nano-multilayer and high entropy nitride coatings, which can be attributed to their moderate valence electron concentration that can not only preserves the formation of strong Me-N bonds but also enables the formation of Me-Me bonds.