The absence of a stable hexagonal Laves phase modification (NbCr 2) in the Nb–Cr system

Abstract

High-temperature differential thermal analysis and neutron diffraction have been employed to investigate the previously proposed polytypic phase transformation C 14 – NbCr 2 ⇄ C 15 – NbCr 2 at around 1600 °C. It could be shown that the phase transformation does not occur for high-purity alloys and high-purity conditions. However, small amounts of atmospheric contaminations induce the formation of an η-carbide-type phase, which melts (partially) in a temperature range around 1600 °C. This led to the earlier erroneous conclusion of the occurrence of a thermodynamically stable high-temperature modification of NbCr 2 .