Liquidus projection of the Nb–Cr–Al system near the Al3(Nb,Cr) + Cr(Al,Nb) eutectic region

The system Nb–Cr–Al was investigated in the region near the Al3(Nb,Cr) + Cr(Al,Nb) eutectic and the liquidus projection of that region was determined based on the microstructural characterization of arc melted alloys. The characterization utilized scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), differential thermal analysis (DTA) and X-ray diffraction (XRD). The results allowed one to determine three primary solidification liquidus surfaces ((Cr,Al)2Nb, Cr(Al,Nb) and Al3(Nb,Cr)), that are originated from the binary systems Cr–Nb, Cr–Al and Al–Nb. It is proposed the occurrence of the invariant reaction L + (Cr,Al)2Nb ⇆ Al3(Nb,Cr) + Cr(Al,Nb) and of a point of minimum, which involves a three phase reaction, L ⇆ Al3(Nb,Cr) + Cr(Al,Nb). All alloys studied showed formation of the Al3(Nb,Cr) + Cr(Al,Nb) eutectic as the last solidification step with Al(Nb)Cr2 precipitating from Cr(Al,Nb).