Wetting of grain boundary triple junctions by intermetallic delta-phase in the Cu–In alloys

The paper studies the wetting of grain boundary triple junctions (GB TJs) by the second solid phase (intermetallic) δ in the Cu–In alloys. In this system, the portion of grain boundaries in a copper-based solid solution (Cu), which are "wetted" by the second solid phase δ, changes non-monotonically with increasing temperature. At first, the portion of such completely wetted GBs increases from zero to almost 100% when the sample is heated, and then quickly falls back to zero. The condition of complete wetting for the GB TJs (σGB > 1.73 σSS) is less stringent than for the GBs (σGB > 2 σSS). Therefore, if the transition from incomplete to complete wetting occurs with an increase in temperature, then all GB TJs should become completely wetted at a temperature TWTJ, lower than the temperature TWGB, at which all GBs become completely wetted. In this work on the Cu–In system, it was found experimentally for the first time that the wetting of the GB TJs also behaves non-monotonously. The percentage of wetted GB TJs also increases to 100% at first and then falls with increasing temperature. In this case, the portion of wetted GB TJs exceeds the portion of wetted GBs not only when it increases with increasing temperature, but also then, with the subsequent disappearance of fully wetted GBs. Grain boundary triple junctions in (Cu-In) solid solution are “wetted” by the δ intermetallic in broader temperature interval than grain boundaries.