With the development of nucleation theory,the calculation of phase diagrams(CALPHAD)method and microscopic elasto-plasticity mechanics,it is possible to apply the phase-field method to simulate the γrafting behavior of nickel-base single-crystal superalloys under the conditions of heat treatment,fatigue and creep testing.Based on the experimental progress in γrafting behavior and in combination with the microstructural simulation of the precipitation and rafting of c0phase,this paper reviews the phase-field investigation of γrafting in nickel–base single-crystal superalloys.
Yan ZhaoHongyu ZhangHua WeiQi ZhengTao JinXiaofeng Sun
It is well known that carbides at grain boundaries play an nickel based superalloys. In order to deeply understand the mportant role in affecting mechanical properties of relationship between grain boundary structures and properties, in this work, we have investigated the microstructure of grain boundaries with different misorienta- tion angles in bicrystals of nickel based superalloys. It is found that the bicrystals with smaller misorientation angles contain denser M23C6 but sparse MC particles at grain boundaries, and this kind of bicrystals presents longer stress rupture lives. It was observed that MC carbides were decorated by M23C6 and M6C particles at grain boundaries. The formation of these carbide particles, therefore, is likely due to the local fluctuation of chemical composition around MC carbides. In addition, the orientation relationships between MC carbides and γ/γ1 matrix were also determined.
Xiaoming DongXiaoli ZhangKui DuYizhou ZhouTao JinHengqiang Ye
The effect of Ru on γ＇ precipitation behavior and evolution in single crystal superalloys with different Ru contents were investigated by scanning electron microscopy with energy dispersive spectroscopy,3D atomic probing,differential scanning calorimetry.The results show that the solvus of the γ＇ phase decreases gradually with increasing Ru content in the alloys by casting or by the same solution and aging treatments,the alloy with a larger Ru content yields a smaller γ＇ phase.The addition of Ru increases the growth rate and coarsening rate of the γ＇ phase.Ru mainly distributes in the γ phase,which causes more Re and Mo partition into the γ＇ phase,increasing the absolute value of mismatch and the rafting rate of the γ＇ phase.
The pattern of dendritic growth and distortion of dendritic network in the platform have been investigated by one mold casting with different platform length during directional solidification. As the platform length elongates, the symmetry of dendritic growth along left and right edges gradually worsens in platform base. While the platform length reaches 14 mm, the distortion of dendritic network is first observed in outward platform. It is found that the distortion of dendritic network along platform inside is more serious than that along platform edges. Both [001] deviation and accumulated misorientation along platform inside, up to 9~ and 16.3~, respectively, are far greeter than those along left-outward-right edges. The deformation of dendritic network in a platform may be caused by the asymmetry of the solidification front at the mush zone.
Xiaoli ZhangYizhou ZhouYanyun HanTao JinXiaofeng Sun
A kind of Ni-Cr-Fe-B-Si system amorphous alloy was used as interlayer in transient liquid-phase bonding(TLP bonding)of polycrystalline superalloy K465.The bonding behavior,microstructure feature and the tensile properties of the joints were investigated.There are B-rich phase and Si-rich phase formed in the center of the seam after bonding at 1210℃for 30 min.The isothermal solidification is complete after bonding at 1210℃for 4 h.The relationship of the average width of the remnant eutectic zone and bonding time at 1210℃is nonlinear.The tensile strength of the bonded joint at room temperature and 900℃is comparable to that of K465 alloy.
Ji-De LiuBo LiYuan SunTao JinXiao-Feng SunZhuang-Qi Hu
