Heat-resisting Nb-based material with microstructure control by combining eutectic solidification under high speed cooling, eutectoid decomposition and spheroidization.

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It was found that a proper microstructure composed of Nb and Nb_5Si_3 was obtained by heat treatment of an Nb-18.1Si-1.5Zr alloy uni-directionally solidified with a rate as high as 1500mm/h. Three-dimensional imaging revealed that large Nb grains are formed through the above-mentioned technique. The alloy shows a room temperature compressive ductility of about 2% and the propagation of cracks in brittle Nb_5Si_3 phase is suppressed by surrounding ductile Nb. Ta addition is required to keep the phase transformation route for the microstructure control with addition of Mo and W for strengthening Nb phase which governs the high temperature deformation behavior.