On the effect of purity and orientation on grain boundary motion

The influence of impurities on grain boundary mobility in a Sigma 7 (38.2 degrees [111]) and in an off-coincidence boundary (40.5 degrees [111]) was investigated. The grain boundary mobility was found to strongly depend on grain boundary crystallography and material purity. The measured concentration dependence of activation enthalpy and preexponential mobility factor did not comply with predictions of traditional impurity drag theory. An extended impurity drag theory is presented that takes into account interaction of the adsorbed atoms in the boundary. This theory predicts a concentration dependence of the activation enthalpy. For the Sigma 7 boundary it can explain qualitatively the frequently observed high values of preexponential mobility factor and activation enthalpy. The compensation temperature was found to depend on composition. (C) 1998 Acta Metallurgica Inc.