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 2016-11-15 Cooperative journals: 《金属学报》
Abstract：采用热模拟实验研究了定向凝固与等轴晶U720Li合金的高温塑性变形行为,利用OM,SEM和EBSD分析了不同变形条件下合金的组织特征及动态再结晶机制.结果表明,定向凝固与等轴晶合金的变形抗力均随变形温度升高而降低.定向凝固U720Li合金沿垂直柱状晶方向变形时变形抗力较低,枝晶间协调变形能力良好,未出现裂纹.与等轴晶合金相比,相同变形条件下定向凝固合金的动态再结晶组织均匀;高温塑性变形过程中,定向凝固合金的动态再结晶主要以晶界弓弯和位错塞积方式形核.定向凝固U720Li合金的变形激活能为766 kJ/mol,比等轴晶合金降低了38.6 %,定向凝固合金呈现出更好的热加工特性.
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