Effects of heat treatment on γ′ precipitates and tensile properties of a Ni-base superalloy

Different heat treatments (solution temperatures: from 1100 °C to 1140 °C) were performed to optimize the microstructures improving the mechanical properties of a wrought superalloy GH4151. The solution treatments essentially affected the area fraction of γ′ precipitates and the grain size of γ matrix. The dissolution kinetics model of primary γ′ precipitates was calculated. The results showed that the fine primary γ′ precipitates inside of grains dissolved first when the solution temperature below 1120 °C, while the coarse primary γ′ precipitates dissolved obviously as solution temperature above 1130 °C. Moreover, the grain growth occurred when the solution temperature exceeded 1130 °C. Besides, a higher area fraction of secondary γ′ precipitates with nearly spherical morphology were precipitated from the matrix during the subsequent aging process. The size of secondary γ′ precipitates increased with the increase of solution temperature. Then tensile tests were carried out at room temperature (RT) and 750 °C, the results showed that the alloy suffered solution treated at 1130 °C possessed the optimum tensile properties at 750 °C on account of the high area fraction of medium-sized secondary γ′ precipitates. However, the strength of alloy solution treated at 1140 °C decreased mainly because of the larger secondary γ′ precipitates. Meanwhile, the fracture mechanism changed from the ductile fracture to a mixed ductile and brittle fracture with the solution temperature rising.