(1. 沈阳工业大学 材料科学与工程学院，辽宁 110870；
2. 贵州工程应用技术学院，贵州 551700；
3. 中航工业北京航空材料研究院，航空材料检测与评价北京市重点实验室，先进高温结构材料国防科技重点实验室，北京 100095)
摘 要: 通过蠕变性能测试和组织形貌观察，研究了铸态TiAl-Nb合金在近750 ℃施加不同应力条件下的蠕变损伤行为。结果表明，合金的组织由不同取向的层片状γ/α2两相组成，不同取向层片状组织的晶界为单一γ相。铸态合金在(750 ℃，300 MPa)蠕变期间的变形机制是位错和孪晶，且位错在层片状γ/α2两相及孪晶中滑移。随蠕变进行，激活的位错数量增加，当蠕变位错与位错网相遇，可改变位错的运动方向，促进发生位错攀移，减缓应力集中。在蠕变后期，大量位错在近相界区域塞积，引起应力集中，可致使裂纹沿垂直于应力轴的层片状γ/α2两相界面萌生与扩展，当不同横断面的裂纹通过撕裂棱相互连接，直至发生断裂，是合金在近750 ℃蠕变期间的损伤与断裂机制。
关键字: TiAl-Nb合金；组织结构；蠕变；变形机制；损伤特征
（1. Shenyang University of Technology, Shenyang 110870; China;
2. Guizhou University of Engineering Science, Bijie 551700, China;
3. Beijing Key Laboratory of Aeronautical Materials Testing and Evaluation, Science and Technology on Advanced High Temperature Structural Materials Laboratory, AVIC Beijing Institute of Aeronautical Materials, Beijing 100095; China）
Abstract:By means of creep properties measurement and microstructure observation, the creep damage behavior of an as-cast TiAl-Nb alloy during various stresses at temperature near 750 ℃ were investigated. The results show that microstructure of alloy consists of lamellar γ/α2 phases, the boundaries with different orientations located in between the lamellar γ/α2 phases are consisted of γ phase. The deformation mechanism of as-cast alloy during creep at (750 ℃, 300 MPa) is twinning and dislocations slipping, and the dislocations slipping within the twins and lamellar γ/α2 phases. In the latter stage of creep, the quantity of activated dislocations increases, the creep dislocations may react with dislocation networks to change their original moving direction when the ones encounter with the networks, which may promote the climbing of dislocations to delay the stress concentration. In the later period of creep, significant amount of dislocations are piled up in the interfaces of the lamellar γ/α2 phases to cause the stress concentration, which may promote the initiation and propagation of cracks along the lamellar γ/α2 interfaces perpendicular to stress axis to display the feature of the trans-lamellar fracture. Wherein, some cracks on the various cross-secions are connected by tearing edge along the direction of maximum shear stress, up to the creep fracture, which is thought to be the damage and fracture mechanism of alloy during creep at 750 ℃.
Key words: TiAl-Nb alloy; microstructure; creep; deformation mechanism; damage feature
