中文摘要：

在2000℃的熔体温度下，实现了Nb-Ti-Si基超高温合金的有坩埚整体定向凝固，并分析了合金定向凝固组织特征．结果表明，合金定向凝固组织分布均匀，定向生长效果显著，主要由耦合生长的层片状（（Nb，Ti）ss＋（Nb，X）5Si3；X=Ti，Hf）共晶团及少量横截面为六边形的（Nb，X）5Si3棒组成．与电子束区熔定向凝固及水冷铜坩埚内的Czochralski法定向凝固比较，有坩埚整体定向凝固时的轴向温度梯度更高，并且避免了区熔定向凝固时存在的固／液界面前沿熔体中的对流和集肤效应，因而合金的定向生长效果更加明显．

英文摘要：

The integrally directional solidification of an advanced ultrahigh temperature Nb-Ti- Si base alloy was carried out with the use of ceramic crucibles at melt temperature of 2000 ℃. The directionally solidified microstructure is revealed. It has been found that the directionally solidified microstructure is composed of couple grown lamellar （（Nb,Ti）ss＋（Nb,X）5Si3） eutectic colonies and a few hexagonally cross-sectioned （Nb,X）5Si3 columns （where X represents Ti and Hf elements）. The directionally solidified microstructure is straightly aligned along the longitudinal axis of the specimens, and is evenly distributed, which showed much superior directionality over those prepared by the floating zone melting directional solidification or Czochralski methods. Compared to both the EBFZM （electron beam floating zone melting） DS process and Czochralski DS process in a water cooled copper crucible, the axial thermal gradient is relatively higher, and the convection in the melt just ahead of the solid/liquid interface and ＂Kelvin effect＂ can be alleviated during the integrally directional solidification process, thus the better directionally solidified microstructure was obtained.