Diffusion of hydrogen along the grain boundaries in Ni3Al alloys

The diffusivity of hydrogen in two Ni3Al alloys (No.1 and No.2) has been me asured in the temperature range of 100 degreesC to 420 degreesC using an ul trahigh vacuum gaseous permeation technique. The diffusivity data fall into two segments, in which the hydrogen diffusivity adheres to the Arrhenius f orm, respectively. From the hydrogen diffusivity, it is conjectured that th e hydrogen diffusivity reflects the hydrogen transportation along the grain boundaries at lower temperature and the hydrogen transportation in the lat tice at higher temperature. The intergranular fracture of Lit-type intermet allics induced by hydrogen at relative low temperature results from hydroge n transportation along the grain boundaries and not in the lattice.