Significant enhancement of the corrosion performance of Ti-6Al-3Nb-2Zr-1Mo alloy via carbon addition in reducing acid environment

In this study, corrosion behaviours of Ti-6Al-3Nb-2Zr-1Mo-xC (x = 0, 0.05, 0.10 and 0.15 wt%) alloys in 5 M HCl solution are investigated. Widmanstätten microstructure, characterized by the obvious prior-β grain boundary, the inside of which consists of lamellar α-phase and intergranular retained β-phase without TiC precipitates, can be identified for all alloys. Electrochemical and immersion measurements signify that C alloying significantly improves the corrosion resistance of Ti-6Al-3Nb-2Zr-1Mo alloy; the corrosion rate dramatically reduces to 0.38 mm·year⁻¹ when C content increases to 0.15 wt%, nearly one-third that of Ti-6Al-3Nb-2Zr-1Mo alloy. Besides, electrochemical parameters demonstrate that the addition of C has few effects on the cathodic hydrogen evolution reaction but noticeable inhibitive effects on the anodic corrosion. Surface characterizations reveal that the addition of C can efficiently alleviate the corrosion degree of prior-β grain boundaries and the lamellar α-phase is preferentially corroded, compared to intergranular retained β-phase.