The permeation of H in superalloy single crystals was studied by using the volumetric method at 573 to 1173K. The experiments were carried out using 2 grades of H-purity, and various sample thicknesses, in order to estimate the effect of the surface upon the permeation rate. It was found that the H permeation at 573 to 870K was controlled by bulk transport. The temperature dependence of the flux reflected anomalies in H solubility and diffusivity in the pure γ-phase, and could be qualitatively explained in terms of a simple model. The activation enthalpy for H permeation lay between the analogous values for Ni (representing the γ-phase) and for pure Ni3Al (representing the γ’-phase). At 870 to 1173K, the permeation was controlled by the kinetics of a sub-surface reaction. The latter was a fully-reversible trapping release at traps which were located in a layer close to the surface. Within this temperature range, the H flux did not depend upon the thickness of the sample.

Permeation of Hydrogen in Ni-Based Superalloy CMSX-4. V.Rothová, I.Stloukal, J.Cermák: Acta Materialia, 2000, 48[4], 827-33