Pressure influence on the grain boundary wetting phase transition in FeSi alloys

Abstract

The influence of hydrostatic pressure up to 1.4 GPa at 905°C on the wetting of grain boundaries in Fe-6 at.% Si and Fe-12 at.% Si bicrystals by a Zn-rich melt has been studied. The dihedral angle θ at the intersection of the grain boundary with the solid/liquid interface has been measured by light microscopy. The transition from complete (θ = 0) to partial (θ > 0) wetting of the grain boundary (dewetting phase transition) was found to occur as the pressure increased. The dewetting transition pressure is higher for special boundaries than for the general boundary studied and decreases with increase in the Si content in the alloy. The pressure effect on the solidus concentration of Zn in FeSi alloys has been determined. This enabled us to construct the surfaces of grain boundary wetting/dewetting phase transitions in three-dimensional phase diagrams in Zn concentration-temperature-pressure and Zn concentration-Si concentration-pressure coordinates. A thermodynamic analysis of the wetting phenomena in binary and ternary systems is given, taking into account the effect of pressure, chemical interactions and structural misfit on the energy of interfaces.