Experimental Measurement Of Interdiffusivities And Calculation Of Diffusion Kinetics In Some Fcc Ni-based Superalloys Systems

Nickel-based superalloys are a kind of extremely important alloy in aerospace field.They are often used to make complex high-temperature parts for their excellent overall performance,long life,good corrosion and wear resistance at high temperatures.On the one hand,the kinetic investigation of superalloys can directly provide the diffusion rates which have important significance for the superalloys’preparation and composition design.On the other hand,conjunction with kinetic databases established by the atomic mobility parameters,computational material science methods can simulate the evolution of superalloys during processing and service and do further research about various diffusion-related processes,such as solidification,creep,and homogenization.This must comprehensively help us design and develop superalloys.The diffusion kinetic research of Ni-based superalloys is incomplete now and the Ni-Ti,Ni-Co are both important subsystems for Ni-based superalloys.In this study,diffusion couple method and DICTRA calclation were used to obtain the interdiffusion coefficient matrices and atomic mobility parameters in fcc regions of Ni-Ti-X(X:Nb,Mo)and Ni-Co-X(X:Ta,Mo)ternary systems.The main contents are as follows:(1)Based on thermodynamic experimental and calculated phase diagrams at 1273 K or 1473 K in Ni-Ti-X(X:Nb,Mo)and Ni-Co-X(X:Ta,Mo)systems,several diffusion couples in fcc phase region of these systems were prepared.The concentration-distance curves at the diffusion interfaces of each diffusion couple were measured and the diffusion coefficient matrix in each system was calculated using the Whittle-Green method.(2)To obtain the thermodynamic parameters of these four systems,and the kinetic parameters of the sub-binary systems from the literature,including Ni-Ti,Ni-Nb,Ni-Mo,Ni-Co,Ni-Ta,and Co-Mo binary systems.Based on the parameters of these binary above and the obtained interdiffusion coefficient matrix during experiments.the atomic mobility parameters of each system were evaluated with the DICTRA software.(3)The obtained mobility parameters were firstly used to calculate the interdiffusion coefficient matrix of each system with DICTRA software.The error between the calculation results and the experimental ones is small.Also,the concentration-distance curves and the diffusion paths were simulated using the mobility parameters,the simulation results agreed well with the experimental values.The reliability of the atomic mobility parameters were verified.