The mechanism involving the effect of disorder/order transformation on the environmental embrittlement in gaseous H2 is summarized. It is shown that there is no hydrogen embrittlement in disordered state of Kurnakov type intermetallics in gaseous H2. However, the H2-induced environmental embrittlement for the ordered alloy having identical chemical composition becomes severer as the degree of the order increases. The results of testing on the ion gage turned on and off during tensile testing show that the more sensitive to H2-induced hydrogen embrittlement for ordered alloy than disordered one is attributed to the fact that atomic ordering may accelerate the kinetics of the catalytic reaction to produce more atomic hydrogen. The results on simultaneous hydrogen charging show that disordered alloys embrittled as hydrogen atoms are forced into the material implying that the embrittlement of ordered alloy in gaseous H2 is also due to the acceleration of the kinetics of catalytic reaction. The above suggestion was further verified by the adsorption tests of Ni3Fe intermetallics powder. It is shown that the amount of chemically adsorbed hydrogen in ordered state is significantly larger than that adsorbed by the disordered alloy, indicating that the more sensitive to H2-induced embrittlement in the ordered state of alloy is essentially due to the accelerated catalytic reaction.
Ultra high vacuum gaseous hydrogen permeation experiments on Fe 3Al based alloy were performed in the temperature range of 330～450℃ with an upstream hydrogen pressure between 3.38×10 4 Pa and 7.28×10 4 Pa. The results show that the hydrogen diffusivity and permeability in Fe 3Al based alloy obey Arrhenius relationship in the experimental temperature range and the hydrogen permeation process is controlled by the lattice diffusion of hydrogen at relative high temperature. The activation energy of hydrogen diffusion in the Fe 3Al based alloy was found to be 75 kJ/mol.
