Grain boundary segregation in the Cu-Bi system

The grain boundary segregation of Bi in Cu polycrystals containing 6, 13, 25, 50, 75 and 102 at.ppm Bi has been investigated. In all studied alloys at certain temperatures (jump temperatures) abrupt changes of the Bi segregation were observed. Below 25 at.ppm Bi the jump temperatures coincide with the solidus temperatures of the Cu-Bi system, while for higher Bi concentrations they deviate upward from the solidus line. At the Bi concentration of 102 at.ppm the Bi segregation decreases and then increases again with increasing temperature. To explain these effects, the concept of a grain boundary solidus line has been suggested. This line is calculated in the framework of the phenomenological prewetting model. Additionally, it was shown that for a one-monolayer thick segregation film on the grain boundary the classical McLean behaviour should be observed, irrespectively of the interchange energy.