Abstract In this study, the microstructural characteristics of directionally solidified (DS) hypereutectic Nb-Si based alloys were investigated. The abrupt acceleration and deceleration of directional solidification were designed to explore the influence of drawing velocity change on microstructure. Results show that the microstructure can be changed by abrupt deceleration, which provides a new possibility to control the properties of DS Nb-Si based materials. The abrupt decelerated solidification for the 17 at.% Si composition is able to scatter the primary silicide slabs, and irregular octahedral primary silicides are finally formed. For the 16 at.% Si composition, the solidification with a constant velocity of 100 mm/min, pseudo-eutectic can be obtained, in which the primary silicides can be eliminated within a certain distance of 4 mm. However, due to the inheritance of the microstructure, the pseudo-eutectic can not be obtained at the same drawing velocity by acceleration from 10 mm/s to 100 mm/s. The directionally solidified microstructure of hypereutectic Nb-Si alloy consists of eutectic and halo microstructures (primary silicides and Nbss shell). Two different growth modes of halo microstructures were identified by EBSD investigations.

中文翻译：

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过共晶 Nb-Si-Ti 合金的定向凝固：拉拔速度变化对显微组织的影响

摘要 在这项研究中，研究了定向凝固 (DS) 过共晶 Nb-Si 基合金的显微组织特征。设计定向凝固的突然加速和减速，以探索拉拔速度变化对微观结构的影响。结果表明，突然减速可以改变显微组织，这为控制DS Nb-Si基材料的性能提供了新的可能性。17 at.% Si 成分的突然减速凝固能够使原生硅化物板片散开，最终形成不规则的八面体原生硅化物。对于 16 at.% Si 成分，以 100 mm/min 的恒定速度凝固，可以获得假共晶，其中初级硅化物可以在 4 mm 的一定距离内消除。然而，由于微观结构的继承性，在相同的拉拔速度下，从 10 mm/s 到 100 mm/s 的加速度无法获得假共晶。过共晶 Nb-Si 合金的定向凝固显微组织由共晶显微组织和晕圈显微组织（原生硅化物和 Nbss 壳）组成。通过 EBSD 研究确定了光晕微结构的两种不同生长模式。