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

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

Automated summary

The effects of different heat treatments on the microstructures and mechanical properties of a wrought superalloy GH4151 were investigated. The solution treatments influenced the area fraction of gamma' precipitates and the grain size of the matrix. A dissolution kinetics model of primary gamma' precipitates was calculated. It was found that the fine primary gamma' precipitates dissolved first when the solution temperature was below 1120 degrees C, while the coarse primary gamma' precipitates dissolved noticeably when the solution temperature was above 1130 degrees C. Additionally, grain growth occurred at solution temperatures above 1130 degrees C. Furthermore, a higher area fraction of secondary gamma' precipitates with increased size was observed with higher solution temperatures. Tensile tests revealed that the alloy solution treated at 1130 degrees C possessed the optimum tensile properties at 750 degrees C due to the high area fraction of medium-sized secondary gamma' precipitates.