Effects of internal and external hydrogen on mechanical properties of beta III titanium alloy sheet

Results of investigation of Ti-base--Mo--Zr--Sn (Beta III alloy), Ti-base--Mo--Cr--Al (VT-15 alloy), and Ti-base-V-Cr-Al (Beta I alloy) show that in the β condition, Beta III is less susceptible to hydrogen elongation (HE) than the other β alloys Beta I and VT 15, similarly H-charged during solution treatment (ST). Not only He, but also H softening can occur in the alloy H charged during various heat treatments. The α-stabilizing effects of cold working (CW) and of previously absorbed O compete with the high temperature β-stabilization by H, decrease H softening and favor HE. The influence of stress state on H effects and the need for sensitive enough tests are again evidenced. A new criterion is proposed to select materials to be stressed in an H environment. H dragging by dislocations plays an important role in HE. This points out the influence of strain rate testing. Furthermore it becomes critically important when environmental degradation depends on film rupture and repassivation. The disk pressure tests are more sensitive than tensile tests and present the adequate sensitivity and versatility to meet the requirements of the complex H effects situation in Ti alloys. With a single set up, using only one specimen geometry, tests can be run at rates ranging from low to high, then the inhomogeneous biaxial stresses involved make them to approach the kind of data usually supplied by impact tests