The present contribution deals with investigations of heat treated Nb-Cu6Sn5 diffusion couples starting from Nb substrate and deposited Cu-Sn layers serving as models for early stages of intermetallic formation during heat treatment of Nb-Cu-Sn wires upon the production of Nb3Sn multifilamentary wires. In the last years, in contradiction to the long-term belief, also a ternary phase with the composition Nb0.75Cu0.25Sn2 was found and called “nausite”. This phase is structurally related to the binary NbSn2 phase and derives from the latter one by partial substitution of Nb by Cu and a change of the stacking sequence in the crystal structure.
In this work, due to the treatments NbSn2 and/or nausite were formed in contact to the Nb substrate. It was demonstrated by energy dispersive X-ray spectroscopy (EDX) that both phases exhibit a ternary homogeneity range. EDX measurements indicate the formation of nausite in the range of 300 to 500°C with Cu contents reaching from 6 to 13 at.%.
Problems in distinction of NbSn2 and nausite based on EDX in particular occur in case of very thin intermetallic layers. Hence, in addition electron backscatter diffraction (EBSD) was employed for phase differentiation. However, careful analysis of EBSD patterns was necessary to distinguish the two phases because of their structural similarities which lead to similar EBSD patterns. Nevertheless, slight differences between the patterns can be employed if the image quality is sufficient.