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Delayed fracture of Ni‐Ti superelastic alloys in acidic and neutral fluoride solutions
Author(s) -
Yokoyama Ken'ichi,
Kaneko Kazuyuki,
Moriyama Keiji,
Asaoka Kenzo,
Sakai Jun'ichi,
Nagumo Michihiko
Publication year - 2004
Publication title -
journal of biomedical materials research part a
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.849
H-Index - 150
eISSN - 1552-4965
pISSN - 1549-3296
DOI - 10.1002/jbm.a.20122
Subject(s) - materials science , hydrogen embrittlement , fluoride , hydrogen , fracture (geology) , corrosion , alloy , metallurgy , hydrogen fluoride , environmental stress fracture , composite material , inorganic chemistry , chemistry , organic chemistry
Hydrogen‐related degradation of the mechanical properties of a Ni‐Ti superelastic alloy has been examined by means of delayed fracture tests in acidic and neutral fluoride solutions and hydrogen thermal desorption analysis. Delayed fracture took place in both solutions; the time to fracture was shorter in the acidic solutions than in the neutral solutions with the same fluoride concentration. The time to fracture was reduced in both solutions when applied stress exceeded the critical stress for martensite transformation. In the acidic solutions, Ni‐Ti superelastic alloy underwent general corrosion and absorbed substantial amounts of hydrogen. Fractographic features suggested that the delayed fracture in the acidic solutions was attributable to hydrogen embrittlement, whereas in the neutral solutions, a different fracture mode appeared associated with localized corrosion only in the vicinity of the fracture initiation area. In the neutral solutions, the amount of absorbed hydrogen was much less than that in the acidic solutions, and the delayed fracture was likely to be induced by active path corrosion accompanying hydrogen absorption. The results of the present study imply that the hydrogen‐related degradation of performance of Ni‐Ti superelastic alloys occurs in the presence of fluoride. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 69A: 105–113, 2004