第一代镍基单晶高温合金的小角度晶界组织及室温拉伸性能

Low angle grain boundary microstructure and room temperature tensile properties of the first generation Ni-based single crystal superalloy

采用光学显微镜及扫描电镜研究了一种第一代镍基单晶高温合金小角度晶界的铸态和热处理态组织,并通过实验探索了小角度晶界试样的室温拉伸性能随晶界角度增加的变化规律。结果表明：合金铸态小角度晶界上分布有γ/γ＇共晶组织、粗大γ＇相及少量MC碳化物。热处理后,晶界上的γ/γ＇共晶相已基本消除,MC碳化物仍保留在晶界上。晶界角度较小时,晶界上γ＇相略大于晶粒内部且呈连续分布,晶界角度超过9.0°时晶界间隙逐渐变宽。拉伸试验结果表明,随晶界角度增加,试样的屈服强度逐渐降低。晶界角度低于3.7°时,试样的断裂特征与无晶界试样相同。晶界角度为3.7°时,试样沿晶界断裂。晶界角度大于3.7°时,断口位于扭转侧晶粒。晶界角度大于9.0°时试样未经过屈服阶段而发生脆性断裂。分析表明,晶界角度的增加导致固定侧晶粒、晶界和扭转侧晶粒三者强度关系发生变化以及晶界间隙宽度增大是小角度晶界试样断裂方式变化的原因。

The low angle grain boundary microstructure at as-cast and as-heat-treated states of a first generation single crystal superalloy were observed by optical microscope and scanning electron microscope,and the variation of room temperature tensile properties with grain boundary angle were studied. The results show that γ/γ＇ eutectic,coarse γ＇ phase and a small amount of MC carbides are distributed in ascast low angle grain boundary. After heat treatment,γ/γ＇ eutectic in the grain boundary are basically eliminated,while MC carbides remain in the grain boundary. γ＇ phase distributes continuously in grain boundary and is slightly coarser than that inside the grains. The grain boundary widens gradually when the angle of grain boundary is larger than 9. 0°. The tensile test results show that the yield strength decreases with the increasing of grain boundary angle. When the grain boundary angle is less than 3. 7°,the fracture characteristics of the specimens is the same as that of the specimens without grain boundary. When the grain boundary angle is 3. 7°,the fracture is mainly intergranular. The fracture is found at the reverse grain when the grain boundary angle is larger than 3. 7°. When the grain boundary angle is larger than 9. 0°,brittle fracture without yielding occurs. The analysis shows that the variation of the fracture mode of the low angle grain boundary specimens can be attributed to the dynamic change of the relationship between the strength of the fixed grain,the grain boundary and the reverse grain,as well as grain boundary widening with the increasing of grain boundary angle.