Change of crack initiation and propagation modes in hydrogenrelated failure of a precipitation-strengthened NI-based superalloy 718 under internal and external hydrogen conditions

Yuhei Ogawa, Osamu Takakuwa, Saburo Okazaki, Saburo Matsuoka, Hisao Matsunaga

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

Abstract

The influences of internal and external hydrogen on the tensile ductility loss and fracture behaviors of a precipitationhardened Ni-based superalloy 718 were investigated via slow strain rate tensile (SSRT) testing under hydrogen pre-charged conditions (internal hydrogen) or in gaseous hydrogen environments (external hydrogen). Severe degradation of tensile ductility was confirmed both in internal and external hydrogen conditions, and the degree of such degradation became more significant with increasing hydrogen content or hydrogen gas pressures. Moreover, the loss of tensile ductility was more pronounced in internal hydrogen conditions than external hydrogen environments. In association with such degradation of macroscopic tensile ductility, hydrogen also altered fracture mode from ductile microvoid coalescence to some brittle appearances. Whereas typical intergranular fracture combined with a decent fraction of quasi-cleavage fracture appeared on the fracture surface formed in external hydrogen environments, several types of unique faceted characteristics were found on the fracture surfaces in internal hydrogen conditions. The detailed observation of the mid-sectioned lateral surfaces of post-mortem samples successfully revealed that the observed distinctions consisted of the fracture along grain boundaries and {111} crystallographic planes including annealing twin boundaries, besides the frequency of the cracking along twin boundaries evidently increased at higher hydrogen concentration. On the basis of the series of experimental results, the initiation and propagation mechanisms of those hydrogen-induced cracks are discussed in terms of hydrogen distribution, intrinsic deformation character of the material itself as well as the alteration of plastic deformation mode caused by dissolved hydrogen.

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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  • Cite this

    Ogawa, Y., Takakuwa, O., Okazaki, S., Matsuoka, S., & Matsunaga, H. (2019). Change of crack initiation and propagation modes in hydrogenrelated failure of a precipitation-strengthened NI-based superalloy 718 under internal and external hydrogen conditions. In Materials and Fabrication (American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP; Vol. 6B-2019). American Society of Mechanical Engineers (ASME). https://doi.org/10.1115/PVP2019-93204