Abstract
High-entropy nitride (Al0.34Cr0.22Nb0.11Si0.11Ti0.22)100-xNx coatings were sputter-deposited from an alloy target Al0.34Cr0.22Nb0.11Si0.11Ti0.22. The effects of nitrogen flow ratio and substrate bias on film structure and properties were studied. Stoichiometric nitride coatings with the best hardness were then annealed at various conditions to investigate the oxidation properties. This (Al0.34Cr0.22Nb0.11Si0.11Ti0.22)50N50 coatings were also deposited onto WC/Co substrate with Ti, Cr, and Al0.34Cr0.22Nb0.11Si0.11Ti0.22 metallic interlayers to study the adhesion properties. The cutting test of (Al0.34Cr0.22Nb0.11Si0.11Ti0.22)50N50 coated inserts with optimal interlayer and oxidation resistance was performed on 304 stainless steel and SKD11 tool steel. For comparison, TiN and TiAlN coatings were also prepared for oxidation and cutting tests. The results show that (Al0.34Cr0.22Nb0.11Si0.11Ti0.22)50N50 coatings deposited at nitrogen flow ratio 50% and substrate bias -100 V have the highest hardness of 36 GPa and Young's modulus of 340 GPa. The metallic films exhibit amorphous structures, while all other nitride films are in single FCC structures. This hard coating also possesses outstanding oxidation resistance. The oxide layer on the coating surface was 290 nm after 50 h annealing at 900 °C. The weight gain after thermal ramping to 1300 °C was merely 0.015 mg cm-2. Such an oxidation resistance is superior to other reported nitride coatings. Eight layers of oxides with different compositions were observed in the scale by TEM. The superior oxidation resistance is owing to the protection of the dense Al2O3 layer and inter-connected Si-rich amorphous network. In adhesion test, (Al0.34Cr0.22Nb0.11Si0.11Ti0.22)50N50 coatings with 100 nm Ti-interlayer demonstrate the best adhesion property. The critical load exceeds 100 N, which is better than the commercial demand (60 N). The cemented inserts coated with (Al0.34Cr0.22Nb0.11Si0.11Ti0.22)50N50 and Ti-interlayer show a better milling performance than commercial TiN and TiAlN-coated inserts. This research demonstrates the great potential of application of this high-entropy (Al0.34Cr0.22Nb0.22Si0.11Ti0.11)50N50.coating for cutting tools.