Extraordinary Response of H-Charged and H-Free Coherent Grain Boundaries in Nickel to Multiaxial Loading
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The cohesive strength of 3, v5, and v11 grain boundaries (GBs) in clean and hydrogen-segregated fcc nickel was systematically studied as a function of the superimposed transverse biaxial stresses using ab initio methods. The obtained results for H-free GBs revealed a quite different response of the coherent twinning boundary 3 to the applied transverse stresses in comparison to the other GB types. While the cohesive strength of 5 and 11 GBs increased with increasing level of tensile transverse stresses, the strength of 3 GB remained constant for any applied levels of transverse stresses. In the case of GBs with segregated hydrogen, the cohesive strength of 3 was distinctly reduced for all levels of transverse stresses, while the strength reduction of 5 and 11 GBs was significant only for a nearly isotropic (hydrostatic) triaxial loading. This extraordinary response explains a high susceptibility of 3 GBs to crack initiation, as recently reported in an experimental study. Moreover, a highly triaxial stress at the fronts of microcracks initiated at 3 boundaries caused a strength reduction of adjacent high-energy grain boundaries which thus became preferential sites for further crack propagation.
Keywordsab initio calculations, hydrogen embrittlement, grain boundary, cohesive strength, multiaxial loading
Document typePeer reviewed
Document versionFinal PDF
SourceCrystals. 2020, vol. 10, issue 7, p. 1-12.