The diffusivity of hydrogen in two Ni3Al alloys was measured at 100 to 420C using the ultra-high vacuum gaseous permeation technique. The diffusivity data fell into two segments (table 17, figure 13), in which the hydrogen diffusivity obeyed the Arrhenius relationship. From the hydrogen diffusivity, it was concluded that the hydrogen diffusivity reflected the hydrogen transportation along the grain boundaries at lower temperatures and the hydrogen transportation in the lattice at higher temperatures. The intergranular fracture of Ll2-type intermetallics produced by hydrogen at a relatively low temperature resulted from the hydrogen transportation along grain boundaries and not through the lattice.

Diffusion of Hydrogen along the Grain Boundaries in Ni3Al Alloys. Cheng, X.Y., Wan, X.J., Wu, Q.Y., Sun, X.K.: Journal of Materials Science and Technology, 2001, 17[2], 207-10

Table 16

Hydrogen diffusivity in Ni3Al