Abstract
(AlCrSi0.3TiZr)Nx and (AlCr1.5Si0.3TiZr0.5)Nx coatings were prepared by reactive DC magnetron sputtering in an Ar+N2 atmosphere using two single high-entropy alloy targets of AlCrSi0.3TiZr and AlCr1.5Si0.3TiZr0.5. The influences of nitrogen flow rate and substrate bias on chemical compositions, crystallography, morphology, mechanical properties, and corrosion behavior of the coatings were investigated. Post-deposition annealing temperatures were varied to investigate the change of crystallography and structure of these nitride coatings. The research was mainly divided into three sections. In the first section, (AlCrSi0.3TiZr)Nx and (AlCr1.5Si0.3TiZr0.5)Nx coatings were deposited under various nitrogen flow rate without applying substrate bias. All the (AlCrSi0.3TiZr)Nx and (AlCr1.5Si0.3TiZr0.5)Nx coatings have single NaCl-type face-centered-cubic crystal structure. (AlCrSi0.3TiZr)Nx and (AlCr1.5Si0.3TiZr0.5)Nx coatings exhibit highest hardness of 25.6 GPa and 20.6 GPa. The coatings of the two compositions prepared at middle nitrogen flow rate display the transition from amorphous to crystalline structure, exhibiting worse corrosion resistance due to their less compact microstructure. These coatings prepared at high nitrogen flow rate show the optimum corrosion resistance due to inert nature of nitrides. The corrosion resistance of the coatings is further increased by depositing an Al interlayer. In the second section, (AlCrSi0.3TiZr)Nx and (AlCr1.5Si0.3TiZr0.5)Nx coatings were deposited under various substrate bias. A reduction in the concentration of Al and Si are observed with increasing substrate bias. All the (AlCrSi0.3TiZr)Nx and (AlCr1.5Si0.3TiZr0.5)Nx coatings have single NaCl-type face-centered-cubic crystal structures. The application of substrate bias changes the coatings from columnar to dense structures, which resulting in the improved hardness and corrosion resistance of the coatings. However, applying too high substrate bias causes rougher surface of coating due to ion-induced damages. The highest hardness of (AlCrSi0.3TiZr)Nx and (AlCr1.5Si0.3TiZr0.5)Nx are 34.1 GPa and 35.3 GPa, respectively. In the third section, post-deposition annealing in air was carried out.. Oxidation resistance of (AlCrSi0.3TiZr)Nx coating is up to 800 °C since its FCC crystal structure is destroyed. However, oxidation resistance of (AlCr1.5Si0.3TiZr0.5)Nx coating is improved up to 900 ℃ with thinner oxidized layers In this study, (AlCrSi0.3TiZr)Nx coating exhibits better corrosion resistance and (AlCr1.5Si0.3TiZr0.5)Nx coating exhibits better oxidation resistance. The optimum coating is (AlCr1.5Si0.3TiZr0.5)Nx with application of high substrate bias since it gives the best combination of hardness, corrosion and oxidation resistance.