Wetting transition of grain-boundary triple junctions

The wetting phase transition of grain boundaries (GBs) and grain-boundary triple junctions (GB TJs) by the melt has been studied in the Al–30 wt.%Zn and Al–10 wt.%Zn–4 wt.%Mg polycrystals. The condition of complete wetting is weaker for TJs (σGB > 3σSL) than that for GBs (σGB > 2σSL), σGB being the GB energy and 2σSL being the energy of the solid/liquid interphase boundary. As a result the temperature of TJ wetting transition should be lower than that of GB wetting transition TwGB. It has been experimentally observed for the first time that TJs become completely wetted at TwTJ, which is about 10–15 °C below TwGB.