Halo formation in arc-melted Cr–Nb alloys

Haloes of Laves phase Cr2Nb around the primary dendrites Cr were observed in the arc-melted Cr–12% Nb hypoeutectic alloy, while no halo of non-faceted Cr phase around the Cr2Nb Laves phase occurred in the Cr–20% Nb hypereutectic alloy. This observation differs from the haloes formed in metal–intermetallic alloy systems. An explanation on the formation of Cr2Nb halo was presented by considering the solidification behavior of the leading phase and non-reciprocal nucleation characteristics of the Cr2Nb/Cr eutectic. In the Cr–12% Nb alloy, primary dendrites Cr worked as a good nucleant available for the occurrence of the halo Cr2Nb that subsequently solidified as the leading phase in the eutectic. For the Cr–20% Nb alloy, primary dendrites Cr2Nb first precipitated as the leading phase inducing the eutectic formation, resulting in no halo growth. In addition, the coupled zone of the Cr–Nb alloy was theoretically predicted in agreement with the experimental results.

► Halo Cr2Nb was observed in the arc-melted Cr–12% Nb hypoeutectic alloy.
► No halo occurred in the arc-melted Cr–20% Nb hypereutectic alloy.
► The coupled zone of Cr–Nb alloy has been presented.
► An explanation on the formation of the Cr2Nb halo is proposed.