Great enhancement in corrosion resistance of Ti alloy by Mo element regulating β grain boundary and microstructure

The anti-corrosion performance of Ti64 is promoted by adding Mo element to regulate the β grain boundaries and microstructure. The microstructure of the Ti64, Ti64‐2Mo and Ti64‐4Mo is basketweave microstructure. While the short rod-like α phases and their variants (120° misorientation) are distributed in the large size β grain with secondary β grain boundaries in the microstructure of Ti64‐8Mo and Ti64‐6Mo. When the Mo fraction changes from 0 wt% to 8 wt%, the content of β phases increases from 8.97 % to 91.42 %. The more Mo element is added, the more stable and denser the surface passivate film becomes. It is mainly because the increment of the highest valence metal oxide, the oxide of Mo and the existence of the secondary β grain boundaries. The corrosion resisting property of Ti64‐8Mo (0.18 mm/year) is 3 times higher than that of Ti64. The decrease of corrosion resisting property of Ti64‐2, 4Mo is because the decrease of α phase area and the segregation effect of Mo aggravates the strength of galvanic corrosion. The galvanic corrosion strength of Ti64‐0, 2, 4Mo is greater than that of Ti64‐6, 8Mo, which is because the segregation in Ti64‐6, 8Mo is less and the content of β phase is higher. The high anti-corrosion performance of Ti64‐6, 8Mo is due to the significant increment of β phase content and the change of microstructure and weaker galvanic corrosion strength.