Grain Boundary Wetting Phase Transformations in the ZnSn and ZnIn Systems

摘要

The wetting phase transition of grain boundaries (GBs) by the melt has been studied in the Zn - 6 wt.% Sn and Zn - 5.3 wt.% In polycrystals and Zn bicrystals (two [10 ˉ1 0] tilt GBs with misorientation angles φ = 19° and 66° , and one [11 ˉ2 0] tilt GB with misorientation angle φ = 79°, wetting by the In-rich melt). In the Zn - 6 wt.% Sn polycrystals, the fraction of the completely wetted GBs gradually increases from 20 to 70% with increasing temperature between 260 and 400 °C. In the Zn - 5.3 wt.% In polycrystals, the fraction of the completely wetted GBs gradually increases from 20 to 65 % with increasing temperature between 215 and 395°C. Temperature dependences of the contact angle θ(T) for bicrystals were measured using scanning electron microscopy and light microscopy. θ decreases with increasing T and reaches zero (complete wetting) at a certain temperature T_w. It has been observed for the first time that temperature dependences of contact angle intersect (at about 350 °C). The wetting transformation for Zn GBs is discontinuous (first order): θ(T) dependence is convex, dθ/dT has a break at T_w and θ ～ ((T - T_w)/T_w)^1/2. Tilt GBs in Zn-Sn and Zn-In systems become completely wetted when about 60-70% of GBs with higher energy are already completely wetted in a polycrystal.