On the Embrittlement of Grain Boundaries by Impurities
ARMY MATERIALS AND MECHANICS RESEARCH CENTER WATERTOWN MA
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The segregation of impurities to grain boundaries is shown to produce a reduction in the grain boundary energy, but that this does not necessarily coincide with a tendency toward embrittlement caused by decohesion. Indeed, it is shown that only when certain relationships occur between the composition dependence of the surface and grain boundary energies can there be a true decohesion of the boundary. The criterion for embrittlement, based on boundary decohesion, requires that the ratio the changes in surface and boundary energies increase with concentration of the impurity, or equivalently, that the ratio of the amount of impurity segregated to the surface to the amount of impurity segregated to the boundary increase with increasing impurity concentration. However, since impurity segregation to grain boundaries occurs independent of whether or not decohesion results, an effect of impurities in the vicinity of the grain boundary on localized plasticity is likely to be the dominant factor in intergranular embrittlement of otherwise ductile materials.
- Metallurgy and Metallography