Grain boundary wetting phase transitions in peritectic copper–cobalt alloys

The transition from incomplete to complete grain boundary wetting in copper alloys with 2.2 and 4.9 wt % Co has been studied. These alloys with peritectic phase diagrams differ from previously studied systems with eutectic transformation by the fact that the melt layer separating grains from each other is not enriched, but is depleted by the second component (cobalt in this case). The fraction of completely wetted grain boundaries increases with temperature, as in eutectic systems, from zero at a temperature of 1098$^\circ$C to $\sim$80% at 1096$^\circ$C. For symmetric twin boundaries, the temperature dependence of the contact angle with melt drops is constructed. As in the eutectic systems, the contact angle decreases with increasing temperature (although not to zero due to the extremely low energy of symmetric twin boundaries).