一种第二代镍基单晶高温合金1150℃原位拉伸断裂机制研究

Investigation of In Situ 1150 ℃ High Temperature Deformation Behavior and Fracture Mechanism of a Second Generation Single Crystal Superalloy

通过自主研发的原位加热拉伸测试平台,在SEM中对[001]取向的第二代镍基单晶高温合金进行了1150℃高温拉伸测试,并得到了可靠的力学性能实验数据与高质量的实时序列SEM像。对力-位移曲线的分析表明,该单晶高温合金在1150℃的屈服强度与断裂强度分别为580与620 MPa。通过分析拉伸过程中的实时序列SEM像,发现该单晶合金在弹性变形阶段γ与γ′相并未发生明显变化;当进入塑性变形阶段,单晶合金中γ相在平行于应力轴方向变形被拉长,同时裂纹在样品原始显微孔洞垂直于应力轴方向最先产生,随着应力的增大绕过γ’相在γ相中扩展,最终裂纹连接相邻孔洞导致单晶合金断裂。

Single-crystal superalloy is the key material of turbine blade and hot end parts in aerospace field. The second generation nickel-based single crystal superalloy has been widely used because of its low cost and excellent high temperature properties. At present, the research on microstructure of superalloys at high temperature mainly depends on SEM and TEM observation after heating and loading experiment. However, such kind of work lacks real-time characterization capabilities. Carrying out in situ experiments has an important significance for understanding the real time deformation behavior and micro-structure evolution of superalloys. Therefore, the development of an in situ high temperature(above1000 ℃) mechanical testing equipment for SEM faces huge challenges. In this work, high temperature tensile experiment at 1150 ℃ of a second generation single crystal nickel-based superalloy were carried out by means of a self-developed in situ heating tensile platform which can used in SEM. A high quality experimental data and serial SEM images were obtained in the course of tensile testing at 1150 ℃. The analysis of force-displacement curve shows that the yield strength and fracture strength of the specimen are 580 and 620 MPa, respectively. The sequential SEM images during this research confirm that there is no obvious shape and size change for γ and γ′ during the elastic deformation, and microstructure changing during plastic stage is mainly due to γ phase widening which is parallel to the stress axis. The results show that the original micro-voids of samples are the weakness in high temperature tensile test at1150 ℃, the fracture direction is almost perpendicular to the stress axis, the crack propagated by passing the γ′ phase and through in the γ phase, and ultimately, temperature and stress induced adjacent holes connection leading to the sample fracture.