Jiro Saga1 and Setuo Miyata2
1Faculty of Engineering, Science, Osaka University, Toyonaka
The behavior of hydrogen electrolytically occluded in pure nickel and fcc nickel-iron alloys was studied by means of X-ray diffraction.
Main results obtained are as follows:
(1) All the materials annealed and then charged with hydrogen showed peak shifts of the γ phase to the lower angles (expansion) and unsymmetric peak broadening.
(2) Two kinds of hydrides, one with a fcc structure and another a hcp structure, were precipitated by supersaturated hydrogen.
(3) The hydride Y having the fcc structure and a lattice parameter several percent larger than that of the matrix was observed in all the materials used. The other X having the hcp structure was observed in pure nickel only.
(4) The tendency for fcc hydride formation was decreased by alloying with iron, because the amount of hydrogen in solid solution increased with increasing iron content.
(5) By aging the materials at room temperatures after hydrogenating, the unstable hydride was decomposed and the matrix was contracted by the hydrogen evolution from the specimen surface. Various structural damages, however, were observed on X-ray diffraction patterns: The ε phase (hcp) stable at room temperatures was formed in nickel-iron alloys, and broadened γ peaks, far from being sharpened, still continued to broaden during the aging process.
(6) Metallographic examination of the hydrogenated specimens indicated the generation of many inter- and transgranular cracks.
(7) The formation of the cracks and broadening of γ peaks are related to the decomposition of hydride Y.
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