Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： GH4169 alloy is widely used to make aero engine, gas turbine as it is one of the most important superalloy. g'' phase is the main strengthen phase, however, the metastable g'' phase will transform to stable d phase during aging or servicing for certain time. d phase is significance in the alloy, its precipitating and distributing behavior have an effect on the properties of the alloy. In recent year, researchers pay more attention on electric field treatment (EFT), this is because of high energy density, accurate controlling, clean and safety. EFT is one of the most important energy field except temperature field and stress field. In this work, EFT was performed on GH4169 superalloy to investigate the influence of EFT on precipitation behavior of d phase in the alloy, and the mechanism of the effect of EFT on the phase transformation was also discussed. The results show that d phases precipitate on the grain boundaries after EFT with 8 kV/cm at 850 ℃ for 15 min, and large amounts of g'' phases precipitate inside the grains. With the increasing of EFT time, both the volume fraction and the size of d phase increase, at the same time the size of g'' phase increases. The volume fraction of d phase is less and the size of d phase is smaller, and the volume fraction of g'' phase is higher by EFT, compared with that by aging treatment (AT) for the same time. In addition, the Nb content on the grain boundary decreases and both Fe and Cr content increase, meanwhile the lattice parameters of c decreases and a, b increase. The vacancy concentrations can be accelerated by EFT, so that the diffusion of Fe and Cr atoms can be promoted. Meanwhile, the Nb atoms in d phases on the grain boundaries can be displaced by Fe atoms and Cr atoms, therefore the Nb atoms are dissolved into the grain. The nucleation rate of g'' phases increases with the increasing of vacancy concentrations. The vacancies relax coherent distortion between g phases and g'' phases, and suppress g'' phases to transform to d phases. Thus the stabilization of g'' phases is enhanced.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： GH4169 superalloy is one kind of important metallic materials used for manufacturing turbine discs in aero-engine. In order to meet the demand of higher strength, high ratio alloying elements have to be added, resulting in the complex microstructure evolution during the long- term service at elevated temperature. Furthermore, the turbine disc usually bears overloading which will lead to the low cycle fatigue (LCF) damage in real working and result in fatal security problem. Besides, it is meaningful to decide the relationship between the microstructure evolution and performance degradation. In the present work, microstructure evolution and LCF behavior of GH4169 alloy during long- term aging were investigated. The microstructure evolutions of GH4169 alloy during long-term aging at 750 ℃ for 500, 1000, 1500 and 2000 h and the influences of long-term aging on the LCF behavior were investigated. The results show that the size of g ″ phases increases and the volume fraction decreases with the increase of aging time, compared with the increase of both size and volume fraction of d phases. Both the fatigue strength and fatigue life of the alloy decrease with the increase of aging time. For the specimen aged for the same time, the cyclic stress firstly contributes to cyclic hardening, then cyclic stability, and finally cyclic softening with the increase of cyclic numbers. It is found that the decrease of cyclic stress contribution is slightly effected by the size of g ″ phases increase and volume fraction decrease after long-term aging. Therefore, the LCF life of the alloy decreases since the crack easily propagates along with the long needle-like d phases and the g ″ phases precipitate free zones.
Hits
Hits
Downloads
Comment