Fracture and deformation behavior in slow-strain-rate tensile testing of Cu-Ni alloy with internal hydrogen

Kentaro Wada, Junichiro Yamabe, Yuhei Ogawa, Osamu Takakuwa, Takashi Iijima, Hisao Matsunaga

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

The effect of hydrogen on the deformation and fracture behavior in pure Cu, pure Ni and Cu-Ni alloy was studied via tensile tests of H-charged, smooth and circumferentially-notched specimens at room temperature (RT) and 77 K. Hydrogendiffusion properties were determined by the desorption method. To obtain a uniform hydrogen concentration in the H-charged specimens, specimens were exposed to 100-MPa hydrogen gas at 543 K for 200 h, based on the determined hydrogen diffusivity. In tensile tests of smooth pure Ni and Cu-Ni alloy specimens at RT, common hydrogen effects were detected, namely, an increase in yield and flow stresses-a hardening effect; and a ductility loss that was accompanied by a change in fracture surface from ductile to brittle feature-an embrittling effect. With regard to the embrittling effect, the pure Ni and Cu-Ni alloy showed different fracture-surface morphologies at RT; the pure Ni showed an intergranular (IG) surface and the Cu-Ni alloy surface was flat. However, a number of IG cracks were detected beneath the fracture surfaces on the smooth Cu-Ni alloy. The tensile tests of the H-charged smooth specimens at 77 K yielded an IG surface for the pure Ni and a ductile fracture surface with dimples in the Cu-Ni alloy. In contrast, tensile tests of the Hcharged, notched specimens at RT demonstrated clear IG fractures for the pure Ni and Cu-Ni alloy. These facts indicate that IG cracking was the first step in the embrittling process for the pure Ni and Cu-Ni alloy, and IG cracking was accompanied by a large plastic deformation that formed the flat surface (unclear IG surface) for the smooth Cu-Ni alloy. Considering that the HE of both pure Ni and Cu-Ni alloy was related to IG cracking, possible mechanisms were discussed and tensile tests performed at 77 K suggested two possibilities: (I) interaction between hydrogen-moving dislocation is more important in the HE process of the Cu-Ni alloy compared to the pure Ni; (II) hydrogen transportation towards grain boundaries are required to cause the IG fracture in the Cu-Ni alloy.

Original languageEnglish
Title of host publicationMaterials and Fabrication
PublisherAmerican Society of Mechanical Engineers (ASME)
ISBN (Electronic)9780791858981
DOIs
Publication statusPublished - Jan 1 2019
EventASME 2019 Pressure Vessels and Piping Conference, PVP 2019 - San Antonio, United States
Duration: Jul 14 2019Jul 19 2019

Publication series

NameAmerican Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP
Volume6B-2019
ISSN (Print)0277-027X

Conference

ConferenceASME 2019 Pressure Vessels and Piping Conference, PVP 2019
CountryUnited States
CitySan Antonio
Period7/14/197/19/19

All Science Journal Classification (ASJC) codes

  • Mechanical Engineering

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