Hydrogen damage process of dual-phase Ti-6Al-4V alloy: From surface passive film to the interior substrate

Ti alloys show promising application prospects in marine field due to their excellent corrosion resistance. However, hydrogen damage of Ti alloys is inevitable during the actual applications in view of the high susceptibility of Ti to hydrogen. The hydrogen damage process from the surface passive film to the interior Ti substrate of dual-phase Ti-6Al-4 V (TC4) alloy was studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), and secondary ion mass spectroscopy (SIMS). The results indicate that the dense passive film on the surface of TC4 alloy is first replaced by loose corrosion product film which mainly consists of TiH1.5 hydrides, and then hydrogen diffuses into the interior of Ti substrate and forms the hydrides of TiH1.971 which are precipitated along the & alpha;/& beta; interfaces, resulting in the cracks of TC4 alloy. Moreover, the element V which mainly locates in the & beta; phases of TC4 before hydrogen charging is transformed to enrich both in & beta; phases and the hydrides at & alpha;/& beta; interfaces after hydrogen charging.