水素脆化におけるき裂伝播の新たなモデルの提案:～Ni20Crに着目して～

<p>For a structure design in consideration of hydrogen embrittlement, it is necessary to establish an analysis technique to simulate hydrogen-related crack propagation. However, crack propagation cannot be fully expressed by a conventional mechanical analysis, because of uncertainty of microscopic mechanisms of the hydrogen-related crack propagation. Therefore, an analysis of hydrogen embrittlement has been recognized to be difficult. In this study, we newly proposed a mechanism-based analysis model of crack propagation in consideration of hydrogen embrittlement through microstructure observations of a cracked material pre-charged with hydrogen gas. The fracture toughness test of Ni20Cr with hydrogen gas charging was performed, and the specimen was observed by electron channeling contrast imaging (ECCI) and electron backscattered diffraction (EBSD) technique in a scanning electron microscope. The entire fracture surface showed intergranular fracture, and the cracks propagated along grain boundaries. Small chinks along grain boundaries ahead a crack tip were observed, and deformation localization associated with the small chinks was observed in the grain on one side of the grain boundary. From the above facts, the following new model of crack propagation in hydrogen embrittlement of Ni20Cr was proposed; The crack propagation of some cracked materials with hydrogen gas charging occurs via repetition of the crack generation.</p>