低循环疲劳试验后GH4720Li轮盘组织及高温力学性能研究

The Microstructure and High Temperature Mechanical Properties of GH4720Li Wheel Disc after Low Cycle Fatigue Test

摘要:

为充分利用发动机现有试验资源,判断GH4720Li合金在发动机服役条件下的显微组织和力学性能变化,从而提高发动机整机试车的一次成功率。本研究对GH4720Li镍基高温合金轮盘进行了系统的低循环疲劳实验,重点观察了试验后齿根、中心孔、过渡弧、榫槽和轮缘等位置的微观组织,研究了不同位置处显微硬度及650 ℃高温力学性能。结果表明,中心孔区域为应力集中最明显部位,该位置γ基体晶粒尺寸明显增大,一次γ′相数量明显减少,部分区域一次γ′相变形后呈水滴状,少量区域出现一次γ′相聚集现象。EBSD分析揭示了小角度晶界主要分布在晶粒内部,呈球形或近球形,尺寸较小；大角度晶界主要分布在晶界和晶界附近。结合已有微观组织可知,小角度晶界主要分布在二次γ′相处,大角度晶界主要分布在晶界及一次γ′相处。TEM表明一次γ′相可以有效阻碍滑移带的扩展,位错多出现在二次γ′相增强相边界和三次γ′相处。650 ℃拉伸结果表明,该轮盘不同位置的高温力学性能保持一致,其抗拉强度均为~1370 MPa,屈服强度为~1090 MPa,延伸率为~25%,表现为韧性断裂特征。上述结果表明,GH4720Li轮盘经低循环疲劳实验后,仍具有较好的高温力学性能,表明其在复杂载荷作用下,没有出现较大的应力集中或变形位置,轮盘完整度高。

Abstract:

In order to make full use of the existing test resources of the engine, the microstructure and mechanical properties of GH4720Li alloy under the service conditions of the engine are judged, so as to improve the one-time success rate of the whole engine test. In this study, the low cycle fatigue test of GH4720Li nickel-based superalloy disc was carried out systematically. The microstructure of the root, center hole, transition arc, mortise and flange after the test was observed, and the high temperature mechanical properties at 650 °C at different positions were studied. The results show that the central hole area is the most obvious part of stress concentration, where the grain size of γ matrix increases significantly, and the number of primary γ′ phase decreases significantly. In some areas, the primary γ′ phase is deformed into water droplets, and a small number of areas appear a γ′ phase aggregation phenomenon. EBSD analysis reveals that the low-angle grain boundaries are mainly distributed inside the grains, which are spherical or near-spherical and small in size. High-angle grain boundaries are mainly distributed near grain boundaries and grain boundaries. Combined with the existing microstructure, it can be seen that the small angle grain boundary is mainly distributed at the secondary γ" phase, and the large angle grain boundary is mainly distributed at the grain boundary and the primary γ" phase. TEM shows that the primary γ" phase can effectively hinder the expansion of slip bands, and dislocations mostly appear at the boundary of the secondary γ" phase and the cubic γ" phase. The tensile results at 650 °C show that the high temperature mechanical properties of the disc at different positions are consistent. The tensile strengths are all kept at ~ 1370 MPa, the yield strengths are ~ 1090 MPa, and the elongations are ~ 25%, which shows the characteristics of ductile fracture. The above results show that the GH4720Li disc still has good high temperature mechanical properties after low cycle fatigue test, indicating that there is no large stress concentration or deformation position under complex load, and the integrity of the disc is high.