Order–Disorder Morphologies in Rapidly Solidified Ni3Ge Intermetallic

Abstract

Congruently melting intermetallic, single-phase Ni3Ge (Tm = 1132°C) has been rapidly solidified via drop-tube processing wherein powders, with diameters between  850 to ≤ 38 m, with equivalent cooling rates of ≤ 700 to > 54500 K s-1 , were produced. Six dominant solidification morphologies were identified with increasing cooling rate, explicitly; (i) spherulites, (ii) mixed spherulites & dendrites, (iii) dendrites-orthogonal, (iv) dendritesnon-orthogonal, (v) recrystallized, and (vi) dendritic seaweed, are observed imbedded within a featureless matrix. Selected area diffraction (SAD) in the transmission electron microscope (TEM) analysis confirmed that it is only the spherulite microstructure that is partially ordered amongst the above listed microstructures, which are disordered. However, SAD analysis indicated that the featureless background material of all above microstructures is chemically ordered. Thermal analysis indicates a non-reversible reaction.