Experimental Evidence of Iron Segregation in Copper Grain Boundaries as Deduced from Type B Diffusion Measurements

Grain-boundary heterodiffusion of iron in pure copper and self diffusion of iron in copper-0.091at% iron were measured by the serial sectioning technique in the Harrison B-regime. The penetration profiles corresponding to iron heterodiffusion in pure copper show a strong positive curvature far beyond the (D(v)t)(1/2) depth. This peculiar shape, which does not exist for self diffusion in the solid solution, proves the presence of a strong non linear grain-boundary segregation of iron in copper in spite of the respective surface energies of these metals. This segregation is linked to the size effect which is, as predicted by numerical simulation, the main driving force for grainboundary segregation.