The effect of a grain boundary structural transformation on sliding in <1010>-tilt zinc bicrystals

Abstract

The effect of temperature on grain boundary sliding has been studied for <10l0) tilt boundaries with different misorientations in zinc bicrystals. The temperature dependence of the average sliding rate for high-angle grain boundaries changes at certain transition temperature T_c , which changes from 0–7T_m to 0–9T_m, where T_m is the melting temperature. Above the transition temperature T_c the activation energy for sliding is about 40 kJ mol⁻¹, but below T_c it is about 100 kJ mol⁻¹ almost irrespective of the misorientation angle. The transition temperature T_c depends strongly on the misorientation angle; the highest value was obtained on a 54–2°<1010> tilt boundary, which is slightly off the 56–6°<1010>/σ9 near-coincidence orientation relationship. For a 16–5° low-angle tilt boundary, no change in the temperature dependence was observed over the entire test temperature range up to the melting point, and the activation energy for sliding is similar to those for high-angle grain boundaries below T_c. It has also been found that the activation energy and the transition temperature T_c can be affected by the purity of the material.

The observed change in the temperature dependence has been attributed to the occurrence of a grain boundary phase (structural) transformation at the transition temperature which depends on the misorientation angle. It is concluded that the low-temperature structure of low-angle or coincidence grain boundaries is much more thermally stable than that of high-angle general grain boundaries in zinc.