Mechanical and electrochemical properties of (MoNbTaTiZr)1-xNx high-entropy nitride coatings

Abstract

High-entropy materials possess high hardness and strong wear resistance, yet the key bottleneck for their practical applications is the poor corrosion resistance in harsh environments. In this work, the high-entropy nitride (HEN) coatings of (MoNbTaTiZr)1-xNx (x = 0–0.47) were fabricated using a hybrid direct current magnetron sputtering technique. The research focus was dedicated to the effect of nitrogen content on the microstructure, mechanical and electrochemical properties. The results showed that the as-deposited coatings exhibited a typical body-centered cubic (BCC) structure without nitrogen, while the amorphous matrix with face-centered cubic (FCC) nanocrystalline grain was observed at x = 0.17. Further increasing x in the range of 0.35–0.47 caused the appearance of polycrystalline FCC phase in structure. Compared with the MoNbTaTiZr metallic coating, the coating containing nitrogen favored the high hardness around 13.7–32.4 GPa, accompanied by excellent tolerance both against elastic and plastic deformation. Furthermore, such N-containing coatings yielded a low corrosion current density of about 10−8–10−7 A/cm2 and high electrochemical impedance of 106 Ω·cm2 in 3.5 wt.% NaCl solution, indicating the superior corrosion resistance. The reason for the enhanced electrochemical behavior could be ascribed to the spontaneous formation of protective passive layers over the coating surface, which consisted of the dominated multi-elemental oxides in chemical stability. Particularly, noted that the (MoNbTaTiZr)0.83N0.17 coating displayed the highest hardness of 32.4 ± 2.6 GPa and H/E ratio at 0.09, together with remarkable corrosion resistance, proposing the strongest capability for harsh-environmental applications required both good anti-wear and anti-corrosion performance.