A scanning force microscopy technique was used to determine the ratio of grain boundary and surface energies in Cu using the thermal grooving method. Samples of ultrafine grain Cu obtained by four passes of equal channel angular pressing were heat treated in a reducing atmosphere at 400C for 0.25h and at 800C for 2h. The average dihedral angles of the grain boundary grooves after the former and the latter heat treatments were 152.4° and 164.2°, respectively, which could be translated into the difference by a factor of 1.8 in average grain boundary energies. This difference implied that the grain boundaries in ultrafine grain Cu produced by equal channel angular pressing were in a state of high non-equilibrium that cannot be fully relaxed after a short annealing at 400C, but that underwent significant relaxation after annealing at 800C.

A Scanning Force Microscopy Study of Grain Boundary Energy in Copper Subjected to Equal Channel Angular Pressing. Y.Amouyal, E.Rabkin: Acta Materialia, 2007, 55[20], 6681-9