Halo formation in arc-melted Cr-Nb alloys

Haloes of Laves phase Cr ₂Nb 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 Cr ₂Nb 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 Cr ₂Nb halo was presented by considering the solidification behavior of the leading phase and non-reciprocal nucleation characteristics of the Cr ₂Nb/Cr eutectic. In the Cr-12% Nb alloy, primary dendrites Cr worked as a good nucleant available for the occurrence of the halo Cr ₂Nb that subsequently solidified as the leading phase in the eutectic. For the Cr-20% Nb alloy, primary dendrites Cr ₂Nb 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.