The Development of Plate and Lath Morphology in Ni₅Ge₃

Drop-tube processing was used to solidify rapidly a congruently melting, single phase intermeallic Ni₅Ge₃. This process results in the production of powders with diameters that are between 850–53 μm. After etching that occurs at low cooling rates (850–150 μm diameter particles, 700–7800 K s¯¹), an isolated plate and lath microstructure in what is an otherwise featureless matrix constitutes the dominant solidification morphology. By contrast, when the cooling rates are higher (150–53 μm diameter particles, 7800–42 000 K s¯¹), it is isolated hexagonal crystallites within a featureless matrix, which constitute the dominant solidification morphology. The TEM analysis of selected area diffraction shows that plate and lath microstructures are variants of ε-Ni₅Ge₃, which are partially ordered. By contrast, the isolated hexagonal crystallites are revealed to be disordered. However, the featureless matrix of both microstructures are the fully ordered variant of the same compound. The plate and lath has a very different EBSD and GOS signatures to the hexagonal crystallites structure. Histogram of the correlated grain orientation angle distribution across grain orientation in plate and lath microstructure sample from the 300–212 μm fraction showing predominance of low angle grain boundaries. However, grain orientation in isolated hexagonal crystallites from 150–106 μm revealing the distribution typical of random grain orientation.