Effect of adding titanium on corrosion and wear resistance of Al0.7CoCrFeNiTix high entropy alloy

Abstract

High-entropy alloys based on the Al-Co-Cr-Fe-Ni system are considered promising materials for applications exposed to wear and corrosive environments. In this study, the effect of titanium addition on the microstructure, mechanical properties, tribological performance and corrosion behaviour of Al0.7CoCrFeNiTix alloys (x = 0, 0.05, 0.2 and 0.5) produced by arc melting was investigated and compared with AISI 304L stainless steel. Microstructural analyses revealed a gradual evolution from a lamellar Widmanstätten morphology to a more complex multiphase structure with an increasing fraction of BCC/B2 phases and enhanced chemical segregation between Al–Ti–rich and Fe–Cr-rich regions. At the highest Ti content, additional intermetallic phases such as Ni3Ti and σ were identified. Increasing Ti content significantly improved hardness and nanoindentation parameters (H/E and H3/E2), indicating enhanced resistance to plastic deformation under contact loading. Sliding tests performed in 3.5 wt.% NaCl solution showed that the Al0.7CoCrFeNiTi0.2 alloy exhibited the lowest wear factor, approximately 54% lower than that of the Ti-free alloy. The wear behaviour was dominated by abrasive and oxidative mechanisms. Electrochemical measurements indicated that Ti addition reduced the corrosion current density and improved passivation behaviour, while the highest pitting resistance was obtained for the Ti0.2 composition. Localized corrosion preferentially initiated in Al–Ni-rich regions depleted in Cr. Overall, the results indicate that the Al0.7CoCrFeNiTi0.2 alloy provides the most favourable combination of mechanical, tribological and corrosion properties in chloride-containing environments.