Influence of hydrogen on metals behavior. 1 - Mechanical behavior of Ti 6 pc Al 6 pc V 2 pc Sn titanium alloy versus hydrogen: influence of heat treatment and of oxygen content

The mechanical behavior of Ti 6 pc Al 6 pc V Sn alloy during dynamic testing has been investigated versus hydrogen and oxygen content. The hydrogen susceptibility depends only slightly on its microstructure, acicular or equi-axed: it depends much more on conditions of hydrogen contamination and on the thermal history afterward. When the alloy has been stabilized by annealing in α - β and provided hydrogen absorption does not induce phase transformations, hydrogen sensitivity is relatively low: brittleness occurs suddenly but at a high concentration threshold (2000 ppm H), which coincides with hydrogen saturation of β phase. When the alloy includes unstabilized phases, its response to hydrogen changes whether it has been finally annealed or not, in the 300 - 500 C temperature area, prone to ω phase formation. In the absence of such an annealing, a reduction in ductility only occurs at high concentrations (> 1500 ppm H). In the other and, after annealing at 400 C, alloy hardening and a ductility decrease start even at the lowest hydrogen amounts: then hydrogen susceptibility is very high. Low oxygen concentration (up to 2000 ppm) do not sensibly affect the good hydrogen tolerance of this alloy. Beyond 2500 ppm, oxygen, while improving tensile strength, yet severely decreases ductility.