Papers by Author: Zhen Xue Shi

Abstract: An observation was conducted on the microstructures of as-cast as well as solid solution treated the third generation single crystal superalloy DD9 using optical microscope and SEM. The effects of solid solution temperature and time on the eutectic fractions of γ/γ and size of γ of the alloy were investigated. The results showed that the microstructure of DD9 was uniform. W and Re segregated to the dendrite cores while Al, Ta and Nb were enriched in interdendritic regions during solidification. The eutectic fractions of γ/γ reduced with the solid solution temperature raising and the solid solution time prolonging. When solid solution temperature increased to 1340, the eutectic in the alloy was entirely dissolved. The size of γ in dendritic cores was consistent, however the size of γ in interdendritic regions was gradually decreased with the increase of solid solution treatment and time, eventually the sizes of γ were completely uniform at the temperature of 1340

Abstract: The tensile properties of DD6 alloy with twist low angle boundaries were investigated at 760°C, 850°C and 980°C, and the misorientation angle of twist low angle boundaries of the specimens of the alloy varies from 0º to 12º. The results showed that when the angle of low angle boundaries is relatively small, it has a little effect on the tensile properties of the alloy. It is notable that effects of low angle boundaries on the tensile strength are weaker than those on the tensile elongation. The characteristic of quasi-cleavage, intergranular and dimple fracture were observed on the tensile rupture surfaces of the specimens, and the tensile fracture mechanism was discussed.

Abstract: The specimens of low angle boundaries were machined from the second generation single crystal superalloy DD6 blades. The microstructures of low angle boundaries (LAB) were investigated from three scales of dendrite, γ′ phase and atom with optical microscopy (OM), scanning electron microscope (SEM), transition electron microscope (TEM) and high resolution transmission electrion microscopy (HREM). The results showed that on the dendrite scale LAB is interdendrite district formed by three dimensional curved face between the adjacent dendrites. On the γ′ phase scale LAB is composed by a thin layer γ phase and its bilateral imperfect cube γ′ phase. On the atom scale LAB is made up of dislocations within several atom thickness.