Papers by Keyword: γ-Phase

Abstract: Metallography analysis of invar alloys crystallized with different cooling rates has been carried out. The study has demonstrated that velocity of crystallization has an impact on the dispersity of graphite. The higher velocity of cooling, the more dispersive graphite is. The volume percentage of graphite in alloy, crystallized with high cooling rate, is lower than compared with low cooling rate. Crystallization with low cooling rate leads to the reduction of the amount of carbon into γ-phase. The coefficient of thermal expansion is basically depends on the amount of carbon into γ-phase.

Abstract: TEM studies of the ex-service single crystal blade were performed to analyse the microstructural changes which control the degradation of the CMSX-4 superalloy during its exposure in a gas turbine. Microstructural analyses were focused mainly on evolution of the γ-γ’ morphology and examination of dislocation configurations in particular parts of the blade. Between the bottom and tip locations of the blade a pronounced differences in γ-γ’ morphology were observed. TEM analysis of the dislocation substructure showed that at the bottom of the blade the dislocation slip is mainly confined to the horizontal γ channels. Increasing of the temperature and decreasing of stress along the blade height resulted in the γ-γ’ rafting, formation of dislocation networks and intensification of the dislocation climb in vertical γ channels.

Abstract: With the unchanged thermal gradient and withdrawal speed, the effect of melt overheating history on the microstructure of Ni-base single crystal superalloy is investigated. The results show that the dendrite structure and γ' phase in interdendritic area is obviously refined when overheating temperature increased from 1500 °C to 1640 °C and then to 1780 °C. However, the microstructure is coarsen with the holding time is increased from 30 min to 45min and then to 60min when melt is overheated at 1780 for 30min.

Abstract: Low-cycle fatigue property of superalloy GH4586 was investigated using a stress amplitude-controlled mode at 1023K. Fracture surface was examined with a scanning electronic microscopy. It was found that the cyclic life can be illustrated by Manson-Coffin at all strain levels. The fatigue cracks initiate primarily on the surface of the specimen. The plastic strain amplitude responded to the cyclic loading shows higher sensitivity than that of the elastic strain amplitude. It was demonstrated that the failure of the present alloy is in a manner of creep-fatigue feature.