单晶镍基合金蠕变期间γ＇相的定向生长及影响因素

Directional Diffusion and Influencing Factors of Elements during Creep of Nickel-Base Single Crystal Superalloys

通过测算不同成分Ni-Cr-Co-W-Mo-Al-Ta系单晶合金在蠕变期间元素扩散的迁移率和γ′相定向粗化速率,研究了元素之间相互作用对扩散速率及γ′相定向粗化速率的影响。结果表明:在γ′相定向粗化期间,合金中γ′相的筏形化速率随成分和应力不同而变化,且γ′相筏形化时间随施加应力的提高而缩短,其中,元素扩散及γ′相定向粗化的驱动力与施加应力及弹性模量相关。元素之间的相互作用对元素Al的扩散速率有影响,随合金中难熔元素Ta+Mo总含量及Ta/W的比值增加,可提高Al的扩散激活能,降低Al的扩散速率,延长γ′相的筏形化时间。在γ′相定向筏化的扩散场中,由原子偏聚形成有序相是自由能降低的自发过程,其中较大半径的Al、Ta原子迁移至{100}晶面,可形成异类原子结合键及稳定的原子堆垛方式,是形成Ll2结构γ′有序相的主要原因。

By means of calculating the elements diffusion mobility and γ＇-phase directional coarsening rate of Ni-Cr-Co-W-Mo-Al-Ta single crystal superalloys with different compositions, the effect of element reaction on the rate of element diffusion and γ＇-phase directional coarsening was studied. Results show that during the γ＇-phase directional coarsening period, the rafted rate of γ＇-phase changes with composition and stress, and the rafted time is decreased with the stress increasing. The driving force of the elements diffusion and γ＇-phase directional coarsening during tensile creep are related to the applied stress and elastic modulus. Element reaction has effect on the diffusion rate of AI. As the total content of Ta＋Mo and the ratio of Ta/W increased, the diffusion activation energy of Al is increased and diffusion rate decreased, and the rafted time of γ＇-phase is elongated. In the diffusion field of γ＇-phase directional coarsening, the formation of γ＇-order phase is attributed to the concentration of the atoms AI and Ta, which is a spontaneous process of the decreased free energy. The Al, Ta atoms with bigger radius are diffused to {100} planes to form the stable arranging order and the linking bond of the atoms with different kinds, which is a main reason of γ＇-order phase formation with Ll2 structure.