Gradient distribution of reinforced phases B2 and Ti5Si3 enabling tribocorrosion optimization in titanium alloy

The distribution of Ti5Si3 and B2 phases in the Ti-Al-Mo-Si alloys was controlled via electromagnetic levitation coupled with fall casting (EML-FC) technique. The B2 and Ti5Si3 phases as reinforced phases exhibited improved wear resistance, passivation and repassivation capability compared to other constituent phases in the alloy. The volume fraction of these two phases in the Ti50Al42Mo4Si4 alloy was higher than that in the Ti50Al46Mo2Si2 alloy owing to the increase of Mo and Si content. The distribution of these two phases can be further controlled by the EML-FC process to form the gradient distribution with increasing volume fraction from edge to center in alloys. This facilitated the rapid formation of a dense passivation film and caused the gradient corrosion behavior of the alloys to effectively prevent the entire alloy from being corroded. The denser passivation film on the surface of Ti50Al42Mo4Si4 alloy by EML-FC mixed with wear debris and formed a friction film on the alloy surface to provide more effective protection and lubrication for the matrix during tribocorrosion. Moreover, the gradient distribution with the higher volume fraction of B2 and Ti5Si3 phases in the Ti50Al42Mo4Si4 alloy significantly restrained pulling out of the alloy matrix, caused Ti5Si3 and B2 phases to be oxidized to reduce wear on the matrix and effectively enhanced repassivation ability under tribocorrosion condition. Consequently, the corrosion and tribocorrosion resistances of the Ti-Al-Mo-Si alloys were improved.