Numerical simulation and prediction of grain formation and defects, including the stray grain and high angle orientation deviation during directional solidification process of a single crystal superalloy hollow turbine blade are experimentally conducted by means of commercial software ProCAST and backscattering scanning electron microscope. The results show that the initial nucleation amount at the beginning section of the starter block is 104 of magnitude, and the number of grains decreases gradually with the competitive growth, and the number is about 100 at the spiral of the selector. And the orientation distribution of grains is close to <001> direction, with the orientation deviation between 10° and 15°. Moreover, with the increase of withdrawal rate, the curvature of isoline of liquidus of single crystal blade increases, and the tendency to form stray grains defects increases. The grain with a large deviation from orientation blocks the growth of other grains at the first rotating transition site of the selector, and then gradually grows and solidifies to form the final blade.

The effect of heat treatment temperature on the microstructure and the high cycle fatigue property of DD6 single crystal superalloy was investigated. After standard heat treatment, the alloy was hold at 1200°C and 1300°C for 1h respectively, and then air-cooled. The results showed that after heat treatment at 1200°C for 1h, the size of γ′ particles became slightly larger and quite unevenly, at the same time, the serrated γ/γ′ interface appeared. After heat treatment at 1300°C for 1h, the small irregular γ′ particles re-precipitated. In addition, a small number of fine secondary γ′ particles were also observed in the matrix channel of the alloy after primary aging of 1200°C/1h and 1300°C/1h. The high cycle fatigue properties of the alloy by standard heat treatment were higher than that of the alloy by 1200°C/1h and 1300°C/1h, but the decreased degree of 1200°C/1h was much bigger than that of 1300°C/1h. Analysis on fracture surfaces of the alloy at 800°C demonstrated a quasi-cleavage mode.