Effect of γ′ Phase on Mechanical Properties of GH4742 Alloy Aged at Long-Term 650 °C: Tensile and Fatigue
摘要
Tensile and fatigue properties are critical factors to measure the service performance of superalloys in turbine disk applications, with these mechanical behavior characteristics being highly dependent on the morphology of the γ′ strengthening phase. Therefore, this study systematically investigated the effects of aging time on the microstructural evolution, tensile properties, and fatigue crack propagation behavior of GH4742 alloy by designing a series of aging treatments. The results reveal that the GH4742 alloy contains three types of γ′ phases: block or irregular-shaped primary γ′ phases (1-2 μm), petal-like secondary γ′ phases (400-800 nm), and spherical tertiary γ′ phases (10-40 nm). With the extension of aging time, the primary γ′ phases exhibit smoother boundaries and an increased degree of interfacial instability. This microstructural evolution shortens the crack propagation path, resulting in an increase in the fatigue crack propagation rate. When the aging time reaches 1000 h, the alloy exhibits a high yield strength (1018.96 MPa) along with an increased crack propagation rate, which is mainly attributed to the precipitation and coarsening of tertiary γ′ phases. These findings indicate that the a competing relationship between tensile strength and fatigue crack propagation resistance in the aged GH4742 alloy, governed by the characteristics of the γ′ phase. This study provides a theoretical basis for optimizing the mechanical properties of GH4742 alloy through microstructural control.