The tracer grain-boundary diffusion of 51Cr and 59Fe at 773 to 1273K was studied, using serial-sectioning, in material that had been modified with Fe, Cr or Zr. It was found that additions of Fe and Cr, of up to about 6at%, did not alter the activation enthalpy for Cr grain boundary diffusion, whereas alloying with Zr (up to 1.6at%) led to a significant increase in the activation enthalpy for Cr grain boundary diffusion (tables 163 and 164). The values of activation enthalpy for Fe grain boundary diffusion in the same materials were smaller than the activation enthalpies for Cr grain boundary diffusion, and they increased slightly with increasing concentration of Fe or Cr. A decrease in activation enthalpy for Fe grain boundary diffusion, with increasing Zr concentration, was observed in Zr-doped alloys. The results were explained in terms of an atomic-size effect and the differing affinities between Zr and Cr and between Zr and Fe atoms.

J.Cermák, I.Stloukal, J.Růžičková, A.Pokorná: Materials Science Forum, 1999, 294-296, 569-72

Table 163

Arrhenius Parameters for 51Cr Grain Boundary Diffusion in Ni3Al