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.