Microstructure development of unidirectionally solidified (Nb)/Nb_3Si eutectic alloys

摘要

Unidirectional solidification experiments were performed on the (Nb)/Nb_3Si eutectic alloys in the Nb-Si binary and Nb-Ti-Si ternary systems. The effect of solidification rates on microstructure development was studied using an optical floating zone melting furnace within the solidification rates from 10 to 200 mm/h. For the binary invariant eutectic alloy, a planar eutectic microstructure forms at lOmm/h, while cellular eutectic microstructures develop at the higher solidification rates. The orientation relationship between Nb and Nb3Si formed upon planar eutectic solidification is determined as: {110}_(Nb)//{110)_(Nb3Si), and < 112 >_(Nb)//< 001]_(Nb3Si). For the ternary univariant eutectic alloys, the formation of cellular eutectic microstructures is prevailing for all over the rates of solidification. The growth of Nb_3Si is faster than that of (Nb). The size distribution of (Nb) particles spreads widely in an asymmetric manner. The cell size variation against solidification rates is in a reasonable agreement with the theoretical prediction.