The role of hydrogen diffusion and desorption in moisture-induced embrittlement in intermetallics doped with alloying elements

A statistical model was developed to explain effects of alloying elements on moisture-induced embrittlement in intermetallics. This model shows that if alloying elements have strong binding to atomic hydrogen, they may suppress moisture-induced embrittlement by slowing hydrogen diffusion even at low alloying element concentrations. The concentration needed to effectively slow down the diffusion process decreases with temperature. Grain boundary segregation is not a necessary condition to suppress embrittlement as long as the alloying element binds to hydrogen sufficiently strongly and its concentration is above a certain level. In the other extreme, when the binding of hydrogen to the surface is so weak that hydrogen desorption occurs simultaneously as surface diffusion, the model demonstrates that above a certain desorption rate, there may be not enough hydrogen diffusing to the crack tip to cause embrittlement.