Effects of hydrogenation on microstructure of Ti-6Al-4V alloy

The microstructures of hydrogenated Ti-6Al-4V alloy have been investigated using optical microscope (OM) and X-ray diffraction (XRD). Compared with the alloy containing lower hydrogen content, the contrasts of α phase and transformed β structure under optical microscope in the Ti-6Al-4V alloy containing higher hydrogen content are reversed. It was found that the face-centered cubic (FCC) δ hydride precipitated in the hydrogenated 0.579 wt.%H and 0.887 wt.%H alloys by XRD analysis. The quantity of β phase increased in the specimens with increasing hydrogen content after hydrogenation due to the α_H → β_H phase transformation. The diffraction peaks are moved to the lower angles with increasing hydrogen content because of solution of hydrogen atoms in α and β phases when the hydrogen content is lower than the saturation of hydrogen in α and β phases. The diffraction peaks of α and β phases are hardly changed when the hydrogen content of Ti-6Al-4V alloy is higher than the saturation of hydrogen in α and β phases. The diffraction peaks of α phase are broadened after hydrogenation because of microcosmic internal stress in α phase.