一种镍钴基合金的γ′相在高温下析出行为的透射电镜研究

In situ transmission electron microscope study of the precipitation behavior of γ′ phase in a Ni-Co based superalloy under high temperature

本文利用透射电镜原位加热技术和元素分析技术相结合的方法,对一种镍钴基高温合金在800℃保温条件下的第二相析出长大行为进行了原位观测。发现不规则的第二相颗粒在γ基体表面析出,该第二相为Cr原子替代占位的γ′-Ni_3Al结构,Cr、Ti元素的表面偏析以及Ni、Co元素向基体内的扩散造成了该第二相富Cr、Ti而贫Ni、Co的元素分布。长大动力学分析表明,该第二相的析出尺寸与保温时间的三次方根呈线性关系,但其尺寸分布与LSW理论存在较大偏差,主要是由第二相析出密度大、颗粒与基体间非共格弹性畸变、以及颗粒之间的"碰撞"异常长大等原因造成的。扩散热力学分析表明,存在一个由表面扩散主导变为体扩散主导的临界温度,在本实验条件下,第二相的析出长大行为由表面扩散主导。

By using in situ TEM heating and chemical analysis technology, we studied the secondary phase precipitation behavior in a Ni-Co based superalloy during aging at 800 ℃. The precipitation of irregular particles on the surface of the γ matrix was observed. The particles have a Cr-site occupancy γ′-Ni_3Al structure.We also found the Cr-/Ti-rich and Ni-/Co-depleted element distribution of γ′ phase, which could result from the segregation of Ti to the surface,and the diffusion of Ni and Co into the matrix.The particle size is linearly related to the cubic root of the aging time, which is consistent to the classic theory of coarsening kinetic. However, the size distribution deviated from the classical LSW theory significantly, which could be caused by the high precipitation density, particle/matrix incoherent elastic energy, and the abnormal ＂collision＂ growth of the particles. Diffusion thermodynamic analysis shows that surface diffusion is the dominant diffusion mode under our experimental conditions.