Papers by Author: Yuh Fukai

Abstract: The equilibrium concentration of vacancies in metals is invariably enhanced in the presence of interstitial hydrogen atoms – a phenomenon called superabundant vacancy (SAV) formation. It has been recognized that the SAV formation occurs in electrodeposition, as M-, H-atoms and M-atom vacancies are deposited by atom-by-atom process. Effects of SAV formation are described for electrodeposited Ni, Ni-Fe alloys, Fe-C alloys and Cu. Possible implication of SAV formation for corrosion in Al and steels is also briefly described.

Abstract: Atomic diffusion in metals is invariably enhanced by dissolution of hydrogen, in some cases by many orders of magnitude. This is a consequence of the formation of superabundant vacancies (SAVs), one of the general properties of M-H systems. Some examples of H-induced enhancement of interdiffusion in alloys and a detailed investigation of self-diffusion in Nb hydride, NbHx, are described, together with accelerated atomic migration observed in electrodeposited metals, also a consequence of SAV formation in the electrodeposition process.

Abstract: Self-diffusion coefficient of 95Nb in NbHx alloys (x=0.05,0.25 and 0.3) has been determined in the temperature range from 823 to 1323 K by using a serial sputter-microsectioning technique. The self-diffusion coefficient of Nb in the NbHx alloys are larger than that in Nb, suggesting that vacancies are formed by hydrogen dissolution, that is, the formation of hydrogen-induced vacancies. The value of the pre-exponential factor for the Nb diffusion in the NbH0.05 alloy is five times larger than that in Nb, while the difference in the activation energies between the NbH0.05 alloy and pure Nb is small. The self-diffusion enhancement in the NbH0.05 alloy is mainly caused by lowering in vibrational frequencies of atoms in the immediate neighborhood of hydrogen-induced vacancies.