Lattice variations of Ti-6Al-4V alloy with hydrogen content

Effect of hydrogen content on the lattice parameter of Ti-6Al-4V alloy has been investigated by X-ray diffraction. The experimental results show that the solution of hydrogen in the Ti-6Al-4V alloy affects significantly on the lattice parameters of α, β and δ phases, especially the β phase. Furthermore, the critical hydrogen content of δ hydride formation for Ti-6Al-4V alloy is 0.385 wt.%. When the hydrogen content is lower than the critical hydrogen content, the δ hydride cannot precipitate and the lattice parameter (α) of β phase linearly increases with the increasing of hydrogen content. When the hydrogen content is higher than the critical hydrogen content, the δ hydride precipitates and the lattice parameter (α) of β phase varies inconspicuously with hydrogen content. In addition, the effects of lattice variations and δ hydride formation on microstructure are discussed. The α/β interfaces of lamellar transformed β phase become fuzzy with the increasing of hydrogen content because of the lattice expansion of β phase. Compared with that of the Ti-6Al-4V alloy at low hydrogen content (≤ 0.385 wt.%), the contrasts of primary α phase and transformed β phase of Ti-6Al-4V alloy at high hydrogen content (≥ 0.385 wt.%) were completely reversed due to the formation of δ hydride.

Research Highlights
► A novel method for determining δ hydride in Ti-6Al-4V alloy is presented.
► The critical hydrogen content of δ hydride formation is 0.385 wt.%.
► The lattice parameter of β phase can be expressed as follows:a=0.323(1+9.9×-210CH)a=0.3231+9.9×10-2CH.
► Precipitation of δ hydride has a significant influence on the microstructure.
► The α/β interfaces of transformed β phase became fuzzy in the hydrogenated alloy.