Morphology of order-disorder structures in rapidly solidified L12 intermetallics

Utilization of intermetallics in high temperature applications is limited due to their poor room temperature ductility. One route to overcoming this is disorder trapping (and subsequent anti-phase domain formation) during rapid solidification, motivating the study of disorder trapping in intermetallics. The single-phase, L1₂ intermetallic beta-Ni₃Ge has been rapidly solidified via drop-tube processing. At low cooling rates (850 – 500 um diameter particles, 700 – 2800 K/s) the dominant solidification morphology, revealed after etching, is that of isolated spherulites in an otherwise featureless matrix. Selected area diffraction analysis in the TEM reveals the spherulites to be partially disordered beta-Ni₃Ge, whilst the featureless matrix is the fully ordered variant of the same compound. Dark-field TEM imaging has confirmed that the spherulites grow as radially emanating fingers of the ordered phase, with disordered material in the space between the fingers.