Recrystallization often occurs in the production of aero engine turbine blades of single crystal superalloys. It is believed that annealing treatment can reduce the recrystallization tendency, as some of the casting residual stress is released. To evaluate the annealing effect on recrystallization, tensile test is carried out in present study for as-cast specimens of a second generation single crystal superalloy to induce stress. Two different annealing treatments are applied to the prestrained specimens, followed by the solution treatment at 1300°C for 2h. In order to compare the effect of the annealing treatments, the specimens are investigated by x-ray Laue diffraction technique and metallographic observation. According to the comparison, the more effective annealing treatment is recommended.

The effect of boron content on the transverse stress rupture properties of a directionally solidified columnar superalloy is studied in present research. The experimental results indicate that the transverse stress property of the alloy containing 0.015% boron reaches the peak value at 870°C /380MPa while that of the alloy with 0.005% boron is the best at 1100°C/40MPa. At 870°C, dislocation slip is the main deformation mode. Stress concentration is induced when dislocations are hindered by precipitates at grain boundaries and interdendritic regions. And then cracks nucleate due to the stress concentration. In the alloy containing 0.015% boron, no borides precipitate and boron strengthens the grain boundary cohesion by solid solution. At 1100°C, grain boundary movement becomes the main deformation mode. In the alloy with 0.005% boron, the strengthening of grain boundary cohesion decreases comparing with that of alloy with 0.015% boron, and the resistance to grain boundary movement reduces with decreasing B content. Therefore, it results in compatible deformation between adjacent grains, resulting in the longest stress rupture lifetime.