MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
Phase Diagram and Superabundant Vacancy Formation in Cr-H Alloys
Yuh FukaiMasaki Mizutani
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2002 Volume 43 Issue 5 Pages 1079-1084

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Abstract

X-ray diffraction measurements on the Cr–H system were made using synchrotron radiation at high hydrogen pressures and high temperatures, and the phase diagram was determined up to p(H2)=5.5 GPa and T\\lesssim1400 K. Three solid phases were found to exist; a bcc phase (α) of low hydrogen concentrations, x=[H]⁄[Cr]\\lesssim0.03 existing at low hydrogen pressures (\\lesssim4.4 GPa), and two high-pressure phases, an hcp (ε) phase at lower temperatures and an fcc (γ) phase at higher temperatures, both having high hydrogen concentrations x∼1. A drastic reduction of the melting point is caused by dissolution of hydrogen. A gradual lattice contraction observed in the fcc phase indicates the formation of superabundant Cr-atom vacancies (vacancy-hydrogen clusters). Thermal desorption measurements after recovery from high p(H2), T treatments revealed several desorption stages including those due to the release from vacancy-hydrogen clusters and from hydrogen-gas bubbles, and allowed determination of relevant trapping energies.

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© 2002 The Japan Institute of Metals and Materials
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