The effect of non-equilibrium grain boundary segregation on the tensile properties and the electrochemical behaviour of nickel

摘要

The ability of sulphur to segregate to several different sites (dislocations, grain boundaries and surfaces) in polycrystalline nickel is a well known phenomenon which manifests itself through changes in the mechanical properties and in the corrosion resistance of the material [1-7]. Segregation of sulphur to grain boundaries results in a marked reduction in the strain to failure and changes the failure mode from one of ductile microvoid coales-cence to one of intergranular fracture. These deleterious effects were found by some authors [8,9] to be most marked when the segregation conditions allow the formation of a sulphide film at the grain boundary. Sulphur segregation to nickel grain boundaries was also found to increase the extent of hydrogen segregation to grain boundaries and surfaces, thus enhancing the susceptibility to hydrogen embrittlement [10]. These impurity or solute effects have generally been explained either by involving the hypothesis that the impurity weakens the atomic bond across the grain boundary or by considering the interactions between the matrix and grain boundary dislocations [11].