Formation of titanium hydride in Ti–6Al–4V alloy

Use of hydrogen as a temporary element in titanium alloys is an attractive approach for enhancing processability, and also for modification of microstructures and thereby improving final mechanical properties. In this article, microstructures, phases and phase transformations in Ti–6Al–4V alloy specimens containing 0.1, 0.3 and 0.5 wt.% hydrogen has been investigated using optical microscopy, XRD and TEM. It was shown that there are fcc δ titanium hydride plates precipitated in the specimens containing hydrogen 0.302 and 0.490 wt.%. Simultaneously, mass orthorhombic martensite α″ has been found in the specimens as well as δ hydride. One eutectoid transformation mechanism from βH to δ hydride and α based on diffusion transformation theory was presented.