(1. 哈尔滨工业大学 金属精密热加工国家级重点实验室，哈尔滨 150001；
2. 哈尔滨工业大学 材料科学与工程学院，哈尔滨 150001；
3. 山西机电职业技术学院 机械工程系，长治 046011)
摘 要: 通过XRD、OM、SEM和TEM分析铸态合金组织，并进行800~850 ℃、250~325 MPa范围内的高温蠕变性能测试，以探究铸态Ti-46Al-6Nb-2.5V-0.2B4C合金的显微组织及高温蠕变变形与断裂行为。结果表明：该铸态合金为全层片组织，多种形态的TiB于片层团内部及晶界处弥散析出，而C原子则固溶于基体中。根据蠕变性能数据计算， Ti-46Al-6Nb-2.5V-0.2B4C合金在测试范围内的应力指数n和蠕变激活能QC分别为5.71和313.316 kJ/mol。该合金的蠕变变形主要由位错攀移与孪生变形控制，并且蠕变诱导产生动态回复与动态再结晶，发挥软化作用。同时，蠕变过程中Ti2AlC会在TiB与基体的界面处动态析出，并与TiB保持 和 位向关系。此外，该合金的蠕变断裂机制主要为孔洞的萌生和聚合以及裂纹的扩展。
关键字: 高Nb-TiAl合金；显微组织；蠕变；变形机制；断裂机制
（1. National Key Laboratory for Precision Hot Processing of Metals, Harbin Institute of Technology, Harbin 150001, China;
2. School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China;
3. Department of Mechanical Engineering, Shanxi Institute of Mechanical & Electrical Engineering, Changzhi 046011, China）
Abstract:In this paper, the microstructure of as-cast Ti-46Al-6Nb-2.5V-0.2B4C alloy was analyzed by using X-ray diffraction (XRD), optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). And the elevated temperature creep tests at 800-850 ℃ under 250-325 MPa were conducted to investigate creep deformation and rupture mechanisms of as-cast high Nb-containing TiAl alloy. The results show that the as-cast alloy exhibits fully lamellar structure. Besides, TiB precipitates inside lamellar colony or at grain boundary and C atoms exist in the matrix in the form of solid solution. According to creep data, the stress exponent (n) at 800 ℃ and the apparent activation energy (QC) under 300 MPa of Ti-46Al-6Nb-2.5V-0.2B4C alloy are measured to be 5.71 and 313.316 kJ/mol, respectively. Combining microstructure observation by TEM, it is revealed that the creep deformation is controlled by dislocation climbing and mechanical twinning. And dynamic recovery and dynamic recrystallization induced by creep play a softening role. In addition, elements B and C play an important role in improving the creep resistance of high Nb containing TiAl alloys. Particularly, Ti2AlC precipitates dynamically at the interface between TiB and matrix during creep process. Moreover, TiB and Ti2AlC follow the well-established orientation relationship as , . Furthermore, the creep rupture is dominated by the initiation and coalescence of cavities as well as the propagation of cracks.
Key words: high Nb-containing TiAl alloy; microstructure; creep; deformation mechanism; rupture mechanism
