Diffusion of hydrogen in nanocrystalline transition-metal alloys

Abstract

Nanocrystalline Fe 90Zr 10, Fe 603oZr 10, and Fe 60Co 30Zr 10 alloys with average grain sizes of 15 nm to 200 nm were produced by crystallization of melt-spun amorphous ribbons. After hydrogen charging, the diffusion of hydrogen was studied by magnetic after-effect measurements and by thermal desorption experiments. Nanocrystalline Fe 60Zr 10and Fe 60Co 30Zr 10 alloys show a strong concentration dependence of the short-range and long-range diffusion of hydrogen, which is characteristic for a statistical distribution of interstitial site and saddle-point enthalpies. The origin of these statistical diffusion potentials can be assigned to the interfacial regions between the grains possessing a high hydrogen solubility in these alloys. In contrast. Nanocrystalline Co 90Zr 10 alloys show no concentration dependence of hydrogen diffusion. The desorption kinetics observed over a wide range of grain sizes indicate that hydrogen is mainly dissolved within the grains and diffuses very fast in the interfacial regions. Therefore the degassing rate depends on the grain size and follows Einstein's diffusion law.