Hydrogen Effects in Nickel-Embrittlement or Enhanced Ductility.
ILLINOIS UNIV AT URBANA-CHAMPAIGN DEPT OF METALLURGY AND MINING ENGINEERING
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In the present work we have attempted to study hydrogen-related fracture of nickel using a variety of experimental methods with the principle aim of establishing the mechanism of fracture. Fracture of nickel was studied in low pressure hydrogen gas and for specimens containing solute hydrogen using slow strain rate tension tests. both intergranular and transgranular fracture was observed on testing in hydrogen gas depending on the heattreatment and on the pressure of trace impurities such as S, Mn, and Mg. The intergranular fracture mode was correlated with the segregation of S to the grain boundaries as measured by Auger and SIMS techniques. Specimens containing solute hydrogen fractured in an intergranular mode for all heattreatments. Detailed examination of both the intergranular and transgranular fracture surfaces indicated that neither was a truly brittle fracture mode but that both indicated a high degree of local ductility. The effect of hydrogen on the plastic properties of nickel was examined using stress strain techniques and in situ deformation in an environmental cell in the HVEM. It was shown that hydrogen decreases the flow stress of nickel. In situ environmental cell fracture studies in hydrogen gas in the HVEM showed that the fracture process resulted from locally enhanced deformation at the crack tip due to the presence of hydrogen. This was confirmed by in situ fracture studies in the SEM. Author
- Metallurgy and Metallography