“Wetting” Phase Transitions by the Second Solid Phase for Linear Defects (Grain Boundary Triple Junctions)

Abstract

In this work, the wetting phase transition of grain boundaries (GBs) and their triple junctions (GB TJs) by the second solid phase in the magnesium-based alloy EZ33A is studied. The condition for complete wetting for the GB TJ ( $$\left({{\sigma _{{\rm{GB}}}}>\sqrt3{\sigma _{{\rm{SS}}}}}\right)$$ ) is weaker than that for GBs (σGB > 2σSS). Therefore, if the transition from partial to complete wetting occurs with increasing temperature, then all GB TJs should become completely wetted at a temperature TwTJ, which is lower than the temperature TwGB, at which all GBs become completely wetted. For the first time, it was experimentally found that GB TJs are completely wetted at TwTJ = 380±10 °C, which is approximately 70 °Clower than TwGB = 450 ± 10 °C. The wetting phase at the GBs is the intermetallic compound (Mg, Zn)12RE. A similar phenomenon was previously observed for GB TJ wetting with a liquid phase [B. B. Straumal, O. Kogtenkova, and P. Zieba, Acta Mater. 56, 925 (2008)].