Phase relations in the Nb-Ni-Cr systems at 1,100 °C

The isothermal cross section through the ternary phase diagram Nb–Ni–Cr at 1,100 °C was constructed by means of diffusion couples and equilibrated alloys. It was found that nearly 28 at.% of Cr can be dissolved in the µ phase (Nb7Ni6) at this temperature, and the solubility of chromium in NbNi3 is approximately 5 at.%. Under these circumstances the low-temperature (cubic) modification of the NbCr2 Laves phase can dissolve up to 6 at.% of nickel, but further increase of the Ni content (up to approximately 10 at.%) stabilizes the hexagonal (high-temperature) modification of the Laves phase. The presence of this pseudo-ternary compound which is in equilibrium with all binary intermetallics and body-centred cubic (BCC) Nb- and Cr-based solid solutions largely determines the topology of the isotherm at 1,100 °C. The formation of this phase was also observed in the reaction zone between Nb and Ni–Cr solid solution when chromium concentration exceeded 15 at.%.