Undercooling and rapid solidification of Nb-Si eutectic alloys studied by long drop tube

• Published in: Transactions of Nonferrous Metals Society of China Vol. 16; no. A02; pp. 89 - 92
• Main Author: 王育人 董树勇 魏炳忱 李维火
• Format: Journal Article
• Language: English
• Published: National Microgravity Laboratory, Institute of Mechanics,Chinese Academy of Sciences, Beijing 100080, China 01.09.2006
• Subjects: Nb-Si共晶合金; 冷却过度; 快速凝固; 金属间化合物; 长滴管; intermetallics; rapid solidification; Nd-Si eutectic alloys; long drop tube; undercooling
• ISSN: 1003-6326

Niobium-silicide alloys have great potential for high temperature turbine applications. The two-phase Nb/Nb5Si3 in situ composites exhibit a good balance in mechanical properties. Using the 52 m drop tube, the effect of undercooling and rapid solidification on the solidification process and micro-structural characterization of Nb-Si eutectic alloy was studied, The microstructures of the Nb-Si composites were investigated by optics microscope （OM）, X-ray diffraction （XRD） and scanning electron microscope （SEM） equipped with X-ray energy dispersive spectrometry （EDS）. Up to 480 K, deep undercooling of the Nb-Si eutectic samples was successfully obtained, which corresponds to 25% of the liquidus temperature. Contrasting to the conventional microstructure usually found in the Nb-Si eutectic alloy, the microstructure of the undercooled sample is divided into the fine and coarse regions. The most commonly observed microstructure is Nb＋Nb5Si3, and the Nb3Si phase is not be found. The change of coarseness of microstructure is due to different cooling rates during and after recalescence. The large undercooling is sufficient to completely bypass the high temperature phase field.