Presence of έ and ε crystal structures in rapidly solidified intermetallic compound Ni5Ge3

The congruently melting, single phase intermetallic Ni5Ge3 has been subject to rapid solidification via drop-tube processing wherein powders, with diameters between> 850 and 150 µm, are produced. At low cooling rates (> 850 µm diameter particles,< 700 K s−1) the dominant solidification morphology, revealed after etching, is that of partial plate and lath microstructure in an otherwise featureless matrix. At slightly high cooling rates (850–150 µm diameter particles, 700–7800 K s−1) complete plate & lath microstructure observed, again imbedded within a featureless matrix. Selected area diffraction analysis in the TEM reveals that partial plate & lath are the disordered form of έ-Ni5Ge3 in a matrix of the ordered (double-superlattice) form. Partial plate & lath has a very different EBSD to the plate & lath structure. Histogram of the correlated grain orientation angle distribution across grain orientation in partial plate & lath microstructure sample from the> 850 µm fraction showing random grain orientation. However, grain orientation in plate & lath structure from 300 to 212 µm fraction displaying the distribution predominance of low angle grain boundaries.