Disorder-order morphologies in drop-tube processed Ni 3 Ge: Dendritic and seaweed growth

Abstract

The single phase intermetallic β-Ni3Ge has been subject to rapid solidification via drop-tube processing. Droplets spanning the size range 212–38 μm, with corresponding cooling rates of 5800–54,500 K s−1, have been subject to microstructural investigation using SEM. Three dominant solidification morphologies have been identified with increasing cooling rate, namely; (i) well-defined dendrites with orthogonal side-branching, (ii) dendrites with non-orthogonal side-branching and (iii) dendritic seaweed. Selected area diffraction analysis in the TEM reveals that both types of dendrites are the disordered form of β-Ni3Ge in a matrix of the ordered, L12, form. However, the diffraction pattern from the dendritic seaweed cannot be mapped onto a cubic structure, indicating a change in the underlying crystallography coincident with the transition to the seaweed structure.