Abstract:Seiries oscilloscope impact tests were conducted for GH4151 alloy under different heat treatment parameters, then microstructure characteristics and grain boundary properties were investigated by using phase diegram calculation, precipitates and EBSD analysis by SEM and detailed phase structure determined by TEM, the relationship between microstructure evolution and impact toughness of GH4151 alloy was systematically studied. The results show that the percentage of primary γ′ phase gets lower with the inceasing of annealing solution temperature, while the average grain size gets greater. The JMat Pro results depict that for GH4151 alloy there exists a certain amount of μ phase, a type of TCP phase, at the grain boundary, besides the secondary carbides of M23C6. Oscilloscope impact tests show that the crack initiation energy including elastic deformation enegy and plastic deformation energy and the propagation enegy for annealing solutioned specimens were all greater than that of annealing aged ones, resulting the good resistance of crack initiation and propagation and good property of inpact toughness. and the impact toughness gets lower when the specimens were annealing aged due to the smaller crack initiation energy and propagation enegy. Further microstructure analysis by TEM shows that the tested impact toughness values were increased with the increase of average grain size and had little relationship with the properties of grain boundary. The main reasons that the sharp decrease of impact toughness for annealing aged specimens were the finer grain size and M23C6 carbides and μ phase precipitate at the grain boundary.