中文摘要：

采用电阻加热定向凝固炉对Ti-47A1-3Nb-0．3Si合金在抽拉速率为5、15、50、100μm／s下进行定向凝固试验，并观察和分析不同抽拉速率下的固液界面形貌、过渡区和定向生长区凝固组织。结果表明，抽拉速率为5μm／s时，固／液界面以胞状界面向前推进，抽拉速率在15-100μm／s时，固／液界面以树枝状向前推进，且随着抽拉速率的增大，一次枝晶间距减小。当抽拉速率为5-50μm／s时，片层组织与生长方向夹角为45°，当抽拉速率增加到100μm／s时，片层组织与生长方向基本垂直。利用扫描电镜背散射观察定向生长区形貌发现，抽拉速率等于或大于15μm／s时，在柱状晶内部或晶界处形成胞状Al偏析，且出现共晶γ相及Ti5（Si，A1）3相。

英文摘要：

Directional solidification experimems were conducted by resistance-heated furnace and the solid/liquid interface morphologies and microstructures in the transient zone and directional growth zone of Ti-47A1-3Nb-0.3Si alloy were observed and analyzed at the withdrawing rates of 5, 15, 50 and 100μm/s .The result shows that the solid/liquid interface is cellular at the rate of 5μm/s, while the solid/liquid interface is dendritic at the rate ranging from 15 μm/s to 100μm/s. And the primary dendritic spacing decreases with increasing withdrawing rate. The lamellar orientations in the columnar grains are inclined with the angle of 45° to the growth direction at the rate ranging from 5 μm/s to 50μm/s and are vertical to the growth direction when the withdrawing rate increases to 100 μm/s. BSE images show that Al-segregation, eutectic γphase and Ti5（Si, Al）3 phase exist in the columnar grain and grain boundary when the withdrawing rate is about 15μm/s or larger.