Performance of V–Cr–Ti alloys in a hydrogen environment

A systematic study is underway at Argonne National Laboratory to evaluate the mechanical properties of several V–Cr–Ti alloys after exposure to environments containing hydrogen at various partial pressures (pH2). The goal is to correlate the chemistry of the exposure environment with hydrogen uptake by the samples and with the resulting influence on microstructures and tensile properties of the alloys. Other variables examined are specimen cooling rate and synergistic effects, if any, of oxygen and hydrogen on tensile behavior of the alloys. Experiments were conducted to evaluate the effect of pH2 in the range of 3×10−6 and 1 Torr on tensile properties of two V–Cr–Ti alloys. Up to pH2 of 0.05 Torr, negligible effect of H was observed on either maximum engineering stress or uniform and total elongation. However, uniform and total elongation decreased substantially when the alloys were exposed at 500°C to 1.0 Torr of H2 pressure. Preliminary data from sequential exposures of the materials to low-pO2 and several low-pH2 environments did not reveal adverse effects on the maximum engineering stress or on uniform and total elongation when the alloy contained ≈2000 wppm O and 16 wppm H. Furthermore, tests in H2-exposed specimens, initially annealed at various temperatures, showed that grain-size variation by a factor of ≈2 had little or no effect on tensile properties. Also, specimen cooling rate had a small effect, if any, on the tensile properties of the alloy.