Mechanical Properties of Rapidly Solidified Ni5Ge3 Intermetallic

Abstract

The congruently melting, single phase, intermetallic Ni 5 Ge 3 has been subject to rapid solidification via drop-tube processing wherein powders with diameters between 850 -150 m are produced. At these cooling rates (850 -150 m diameter particles, 700 -7800 K s -1 ) the dominant solidification morphology, revealed after etching, is that of isolated plate & lath microstructure in an otherwise featureless matrix. Selected area diffraction analysis in the TEM reveals the plate & lath are a disordered variant of -Ni 5 Ge 3 , whilst the featureless matrix is the ordered variant of the same compound. Microvicker hardness test result shows that mechanical properties improve with decreasing the particle size from 850 to 150 m as a consequence of increasing the cooling rate.

The Development of Plate and Lath Morphology in Ni5Ge3

“…We can infer from the non-detection of these microstructural features that were so evident in the etched samples, that their crystallography must be contiguous with the grains in which they are embedded. This is consistent with TEM diffraction analysis, in which sharp diffraction spots are apparent as found previously [17,18]. The appearance of these spots is consistent with the beam being focused on an area that has a single crystallographic orientation.…”

“…Moreover, in the case of a congruently melting compound the contrast would not be expected to arise from compositional differences in the assolidified material. The absence of solute partitioning is established elsewhere [17,18], where it is shown by EDX line scan across an isolated plate & lath feature [18], that material is chemically homogeneous to within the experimental error related with the technique. This is also the case for the isolated hexagonal crystallites morphology [18], which is similarly shown to be chemically homogeneous across features.…”