| 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 ¯1 0] tilt GBs with misorientation angles φ = 19œ and 66œ , and one [11 ¯2 0] tilt GB with misorientation angle φ = 79œ, 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 œC. 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 395œC. 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 Tw. It has been observed for the first time that temperature dependences of contact angle intersect (at about 350 œC). The wetting transformation for Zn GBs is discontinuous (first order): θ(T) dependence is convex, dθ/dT has a break at Tw and θ ∼ ((T - Tw)/Tw)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. |
full paper (pdf, 320 Kb)