MICROSTRUCTURAL AND CRYSTALLOGRAPHIC RELATIONSHIPS IN DIRECTIONALLY SOLIDIFIED NB-CR2NB AND CR-CR2NB EUTECTICS

The present paper describes processing, microstructures and phase rela tionships in directionally solidified Cr2Nb-Nb and Cr2Nb-Cr eutectics. Both of these eutectics, and the stoichiometric Laves phase Cr2Nb, we re directionally solidified using cold crucible Czochralski crystal gr owth with growth rates from 1 to 15 mm/min. Cr2Nb-Nb had a rod/ribbon- type structure and Cr2 Nb-Cr had a lamellar structure. The crystallogr aphic orientation relationships between both Cr and Nb and the Cr2Nb L aves phase in the individual eutectics were characterized using transm ission electron microscopy. Inter-phase orientation relationships in t hese eutectics were complicated by the transformation of Cr2Nb from th e C14 to the C15 crystal structure on post-solidification cooling. Twi ns were observed in the C15 Cr2Nb phase in both the single phase and e utectic samples. The relationship between the twins, the C14-C15 trans formation, and the eutectic morphology is also discussed.