The Effect of Hydrogen on the Fracture and Slip Behavior of Nickel.
ILLINOIS UNIV AT URBANA DEPT OF METALLURGY AND MINING ENGINEERING
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The introduction of hydrogen into nickel specimens by thermal charging leads to a predominantly intergranular failure mode regardless of sulfur segregation to grain boundaries. Following significant plastic deformation, crack nucleation occurs at grain boundary triple points and along grain boundaries situated within a stress concentration region. Large CODs are generated during crack growth through localized plastic deformation at the crack tip and intense grain boundary shearing. Grain boundary fracture facets show clear indications of such deformation in the form of slip with occasional cracking along slip lines. Secondary cracking at triple points ahead of the main crack is a common occurrence. Transgranular fracture is observed in specimens having no significant sulfur segregation at grain boundaries when strained in H2 gas. Two surface X-ray analysis in Ni single crystals show this fracture plane to be of the 111 type. This type of failure is also accompanied by considerable plastic deformation both prior to crack initiation and during crack growth. The fracture surface markings show evidence of this ductile failure with clear slip lines and tetrahedral hillocks whose faces appear to correspond to intersecting 111 planes.
- Metallurgy and Metallography