title: Hydrogen embrittlement of work-hardened Ni-Ti alloy in fluoride solutions.
abstract: Hydrogen embrittlement of work-hardened Ni-Ti alloy has been examined in acidulated phosphate fluoride (APF) solutions. Upon immersion in a 2.0% APF solution with a pH of 5.0, tensile strength decreased markedly with immersion time. Moreover, the fracture mode changed from ductile to brittle due to brittle layer formation at the peripheral part of the cross section of the specimen. The amount of absorbed hydrogen increased linearly with immersion time, and it reached above 5000 mass ppm after 24 h. The hydrogen desorption temperature of the immersed specimens shifted from 450 degrees C to a lower temperature with immersion time. As the amount of absorbed hydrogen was larger than 500 mass ppm, the degradation of mechanical properties was recognized. Although the tensile properties and fracture mode scarcely change in a 0.2% APF solution, the slight reduction in hardness and hydrogen absorption of several hundreds mass ppm were observed. The results of the present study imply that work-hardened Ni-Ti alloy is less sensitive to hydrogen embrittlement compared with Ni-Ti superelastic alloy.
authors.affiliation: Department of Dental Engineering, School of Dentistry, The University of Tokushima, 3-18-15 Kuramoto-cho, Tokushima 770-8504, Japan. yokken@dent.tokushima-u.ac.jp
authors.forename: Ken'ichi
authors.initials: K
authors.lastname: Yokoyama
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Kaneko
authors.forename: Toshio
authors.initials: T
authors.lastname: Ogawa
authors.forename: Keiji
authors.initials: K
authors.lastname: Moriyama
authors.forename: Kenzo
authors.initials: K
authors.lastname: Asaoka
authors.forename: Jun'ichi
authors.initials: J
authors.lastname: Sakai
mesh_terms: D000042:Absorption; D000149:Acidulated Phosphate Fluoride / Q000737:chemistry*; D001672:Biocompatible Materials / Q000737:chemistry*; D001826:Body Fluids / Q000737:chemistry*; D003343:Corrosion; D004548:Elasticity; D005459:Fluorides / Q000737:chemistry; D006244:Hardness; D006245:Hardness Tests; D006859:Hydrogen / Q000737:chemistry*; D008422:Materials Testing; D009532:Nickel / Q000737:chemistry*; D009969:Orthodontic Wires; D013499:Surface Properties; D013718:Tensile Strength; D014025:Titanium / Q000737:chemistry*
chemical_list: D001672:Biocompatible Materials; C040654:titanium nickelide; D000149:Acidulated Phosphate Fluoride; D009532:Nickel; D006859:Hydrogen; D014025:Titanium; D005459:Fluorides