Determination of activation energy for nanometre-scale grain-boundary sliding in copper

The activation energy Q for grain-boundary-dependent sliding in copper has been measured below 573 K from experiments using an electron microscope on Cu-Fe-Co alloy bicrystals with various [011] symmetric tilt boundaries. The technique utilizes the sliding-induced rotation of moiré fringes in b.c.c. Fe-Co particles on grain boundaries and is capable of detecting sliding of less than 1 nm. It is concluded that grain boundaries slide in a viscous manner with inherent viscosity \ eta = \ etaoT exp(QIRT), where \ etao is a constant related to the boundary structure. The misorientation angle dependences of the values of Q and \ etao display cusps and are similar to that of the boundary energy in copper. The larger the degree of disorder in the atomic arrangement at a boundary, the lower is the boundary viscosity.