ملخص: Impurity segregation to grain boundaries and free surfaces of pure metals is thought to take place according to two mechanisms. One involves the thermodynamic and kinetic laws of equilibrium, as is the case, for example, in annealing for sufficiently long periods at sufficiently high temperatures ([approximate]0.5TM, TM being the melting temperature). The other takes place while a metal, initially in a non equilibrium state is returning to equilibrium, as is the case, for example, during the annealing of a quenched or cold worked metal.In this work, a kinetic study of sulphur segregation taking place during the annealing of both quenched and cold-rolled nickel is carried out.It is found that the sulphur segregation kinetics measured during the elimination of vacancies (quenched nickel) are two-three orders of magnitude higher than the ones predicted by McLean for equilibrium segregation. In the case of the cold worked material, it is found that the kinetics, compared to equilibrium ones, are accelerated by both the vacancy annihilation and the recrystallization stages of the heating process. A considerable reduction in strength and ductility, coupled with severe intergranular corrosion as shown by scanning electron micrographs, may be taken as clear evidence of intergranular segregation taking place during the recovery by the material of its equilibrium state.

لغة: إنجليزية