Phase formation in rapidly solidified R2T17 intermetallics

Rapid solidification was utilized to produce a series of light and heavy rare earth-transition metal intermetallics in the RH-Co, RL-Co/Fe, and Sm-Co(Fe) systems with RH = Dy and Tb and RL = Pr and Sm. The influence of Nb-C and Zr-C additions on phase formation in the binary and ternary alloys has also been investigated. The X-ray diffraction patterns obtained with synchrotron radiation were refined by the Rietveld method for structural phase determination and analysis. It was found that the ability to create disorder strongly depended on the rare earth element, with light rare earth systems possessing more disorder, and rapid solidification effectively suppressed the development of long-range order in these compounds. Cobalt in contrast to iron favored the formation of disordered structures. Replacement up to two out of the three of the cobalt atoms with iron in the Sm-Co-Fe system has retained the establishment of the disordered TbCu7-variant and exhibited complete cobalt-iron solubility. Additions of Nb-C and Zr-C have also greatly influenced the order formation. The comparison of lattice parameters of the intermetallic compounds obtained by rapid solidification to the parameters of equilibrium 2-17 phases summarized in the literature revealed that formation of partially ordered and disordered structures was associated with expansion of the both a- and c-axes in Th2Zn17- and Th2Ni17-type phases for all binary compounds.