The Effect of Diffusive Hydrogen Segregation on Fracture of Polycrystalline Nickel.
ILLINOIS UNIV AT URBANA DEPT OF METALLURGY AND MINING ENGINEERING
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Hydrogen embrittlement of polycrystalline nickel was studied under conditions which allowed the diffusion and segregation of hydrogen to grain boundaries to be controlled. It was shown that even at high solute concentrations of hydrogen, the fracture mode was ductile shear rupture, if transport of hydrogen to the grain boundaries was not allowed. As the amount of hydrogen segregation to the grain boundaries was increased the fracture mode became increasingly intergranular. Analysis of the temperature dependence of this transition from ductile rupture to transgranular fracture yields a hydrogen segregation enthalpy of 11.6 kJmole. The transition in the fracture mode was also observed at a constant temperature by increasing the solute hydrogen concentration. The kinetics of this fracture transition suggests that the high hydrogen segregation layer extends about 35 nm from the grain boundary. It is suggested that the fracture mechanism is a softening of the material in this segregation region due to the high hydrogen concentration.
- Metallurgy and Metallography