Grain-boundary and interphase-boundary diffusion was investigated in the Ag/Ni system by using the radiotracer serial-sectioning technique. Measurements of the grain boundary diffusion of 110mAg in Ni polycrystals were performed, in the type-B kinetic regime, at 973 to 1253K. The results (figure 17) could be described by:

sdD (m3/s) = 5.6 x 10-15 exp[-120.5(kJ/mol)/RT]

The sdD values were higher than those for Ni grain-boundary self-diffusion, while the activation enthalpy was nearly the same. The very low solid solubility of Ag in Ni was expected to lead to strong Ag segregation in Ni grain boundaries. Upon taking this into account, it was deduced that the Ag mobility in Ni grain boundaries was lower than that of Ni.

Radiotracer Diffusion of Ni and Ag in Ag and Ni Grain Boundaries and Oriented Ag/Ni Interphase Boundaries. C.Minkwitz, C.Herzig, B.Straumal, W.Gust: Materials Science Forum, 1999, 294-296, 541-4

Figure 17

Grain-Boundary Diffusivity of Ag in Ni