Phase selection during solidification of undercooled Ni 70.2Si 29.8 eutectic alloy

Abstract

High undercooling (about 392 K) was achieved in the bulk eutectic Ni 70.2Si 29.8 alloy melt through glass fluxing combined with cyclic superheating. It is found that the metastable phases Ni 3Si 2 and NiSi are obtained through slow post-solidification when undercooling exceeds 240 K. The metastable phases are confirmed by using the method of X-ray diffraction and differential scanning calorimetry (DSC). Based on the principle of the free energy minimum and the transient nucleation theory, the phase selection of melt is investigated with regard to the metastable phases formation in the bulk undercooled eutectic Ni 70.2Si 29.8 melts. The formation of metastable phases from undercooled Ni 70.2Si 29.8 melts is ascribed to competitive nucleation with the undercooling, i.e. high undercooling facilitates the preferential nucleation of metastable phases.