Phase relations in the Nb-Ni-Cr system at 1,100 °c

Abstract

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 l phase (Nb 7Ni 6) at this temperature, and the solubility of chromium in NbNi 3 is approximately 5 at.%. Under these circumstances the low-temperature (cubic) modification of the NbCr 2 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 (hightemperature) 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.%. © 2012 Springer-Verlag.