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 μm and ≤ 38 μm, with equivalent cooling rates of ≤ 700 to > 54,500 K s−1, were produced. Six dominant solidification morphologies were identified with increasing cooling rate, explicitly, (I) spherulites, (II) mixed spherulites and dendrites, (III) dendrites—orthogonal, (IV) dendrites—nonorthogonal, (V) recrystallized, and (VI) dendritic seaweed, are observed imbedded within a featureless matrix. Selected area diffraction (SAD) in the transmission electron microscope analysis confirmed that it is only the spherulite microstructure that is partially ordered among these microstructures, which are disordered. However, SAD analysis indicated that the featureless background material of all of these microstructures is chemically ordered. Thermal analysis indicates a nonreversible reaction.