LOW-ANGLE GRAIN-BOUNDARY DIFFUSION OF CR IN NB BICRYSTALS

Grain boundary diffusion of Cr in [110]/[112] symmetrical bcc bicrysta ls of Nb has been investigated in the temperature range from 950 to 11 97 degrees C with tilt angles, theta, from 2 to 21 degrees. For theta less than or equal to 17 degrees, the activation energy is independent of theta, with an average value of 181.2 kJ mol(-1), which is about h alf of the activation energy of lattice diffusion. The grain boundary diffusion coefficients are greater than the lattice diffusion coeffici ents by five or six orders of magnitude and vary linearly with sin(the ta/2), in agreement with the dislocation-pipe model. These conclusions are generally consistent with the findings in fee bicrystals.