Determination of hydrogen diffusivity depending on the hydride concentration in titanium-hydride by means of the diffraction-enhanced X-ray imaging method

The X-ray refraction imaging technique was applied to the quantitative study of hydrogen diffusion in titanium-hydride. Hydrogen diffusivity in titanium-hydride was determined by direct observation of the hydride. The hydride was formed on the surface of titanium by electrolytic-charging at 63°C. The specimens were cut into 1-mm thick slices for cross-sectional observations. The hydride layer was observed using the diffraction-enhanced X-ray imaging (DEI) method with asymmetric analyzer. Boundaries between titanium and the hydride were observed as thick black or white lines parallel to the specimen surface in the DEI images similar to previously reported results. Hydride distribution caused by hydrogen diffusion from the surface was converted to the intensity profiles of refraction images of the hydride using the measured rocking curve from an analyzer. The hydrogen diffusivity was calculated from the intensity profiles using the solution of the appropriate diffusion equation. The obtained hydrogen diffusivity in titanium-hydride depended upon the hydrogen concentration. The diffusivity showed good agreement with the widely accepted values in the low hydride concentration region.