Effect of atomic ordering on the hydrogen-induced environmental embrittlement of Ni4Mo intermetallics

Hydrogen induced environmental embrittlement of a Ni4Mo alloy in different degree of ordered conditions was investigated by tensile tests in various atmosphere. The results show that the disordered Ni4Mo alloy is not susceptible to embrittlement in hydrogen gas, but very susceptible to embrittlement in hydrogen charging. However, for the ordered Ni4Mo alloy, there is similar deterioration in ductility when the environment changes from oxygen to hydrogen gas and simultaneous hydrogen charging. It indicates that the atomic ordering does not influence the dynamic hydrogen charging-induced environmental embrittlement, but has a considerable effect on the gaseous hydrogen-induced environmental embrittlement. In addition, hydrogen absorption and desorption of the Ni4Mo alloy with disordered and ordered structures were also investigated using gas chromatographic analysis. The results show that the atomic ordering can promote gaseous hydrogen absorption at room temperature. This suggests that the atomic ordering accelerates the kinetics of the catalytic reaction for the dissociation of molecular hydrogen into atomic hydrogen due to the change of the outer layer electron structure and therefore exacerbates the hydrogen gas-induced environmental embrittlement.