Occurrence of Faceting for [110] Symmetric Tilt Boundaries in Cu Doped with Bi

The faceting of the grain boundary in the binary Cu-Bi system was experimentally observed by transmission electron microscopy (TEM). For the observation, Cu bicrystals with Sigma 33, Sigma 9 and Sigma 11[110] symmetric tilt boundaries were doped with Bi at 1173 K for 120 h, and then homogenized at 1173 K for 48 h. followed by furnace cooling or water quenching. The misorientation angle between the [001] directions of the two single-crystals is 20.1 degrees, 39.9 degrees and 50.5 degrees for the Sigma 33, Sigma 9 and Sigma 11 boundaries, respectively. According to the TEM observation, the grain boundary is faceted markedly in the bicrystal with furnace cooling but barely in that with water quenching. Thus, the faceting takes place during furnace cooling but not during homogenization. The faceting was analyzed quantitatively on the basis of the inclination angle dependence of the boundary energy in Cu. The analysis yields that the contribution of the torque term to the faceting is important. Comparing the boundary diffusivities of Bi and Cu in Cu, we may expect that the mobility is much greater for the grain boundary with Bi than for that without Bi. As a result, the faceting during furnace cooling takes place considerably for the grain boundary with Bi but scarcely for that without Bi. [doi: 10.2320/matertrans.MRA2008062]