Effect of Microstructure Characteristics on Impact Toughness of GH4151 Alloy

Abstract:

The GH4151 alloy samples after different heat treatments were tested using instrumented impact testing, and the effects of microstructural characteristics and grain boundary features on the impact toughness of GH4151 alloy were analyzed through metallographic microscope, scanning electron microscope, transmission electron microscope, and phase diagram calculations. The results show that the percentage of primary γ′ phase decreases with the increase in solid solution temperature, while the average grain size gradually increases and the impact toughness of the solution-treated alloy also gradually increases. The results of phase diagram calculation by JMatPro depict that there is a certain amount of μ phase (a type of TCP phase) at grain boundaries and M₂₃C₆. Analyses of the instrumented impact curves and fracture surfaces reveal that for the alloy subjected to solution treatment only, the elastic deformation work (E_e), plastic deformation work (E_p), and tearing work (E_c) are all relatively large, indicating a good resistance to crack initiation and propagation and a high impact toughness. After solution treatment followed by two-stage aging, both the E_e and E_p become significantly smaller, and the E_c even approaches zero, resulting in a substantial decrease in impact toughness. Compared with the sample subjected to solution treatment only, the significant reduction in impact toughness of sample after two-stage aging is primarily attributed to grain refinement and the synergistic precipitation of grain boundary μ phase and M₂₃C₆ carbides during aging, while showing relatively little correlation with the grain boundary characteristics of the matrix.