Study On Diffusion Kinetics In Some Co-based Ternary Alloys

Due to their excellent high temperature strength, good anti-oxidation, corrosion resistance and anti fatigue etc. comprehensive performance, superalloys have become the key materials for turbine engine hot end components. According to the high temperature alloy matrix, materials can be divided into Fe-based superalloys, Ni-based superalloys and Co-based superalloys. As an important high temperature alloys in high temperature environment, Co-based alloys have excellent high temperature strength, good corrosion resistance, anti fatigue and anti wear ability, especially anti corrosion ability. These superior properties make them more unique, when compared with Ni-based superalloys. However, research on Co-based alloys is relatively rare. In the design of new Co-based superalloys, understanding of the microstructure and the relationship between processing and properties of Co-based alloys is very important. Modern material design method is based on combination of thermodynamic phase diagram calculation and diffusion dynamics simulation. The thermodynamic and kinetic databases can support important information for simulation. The database size, reliability and the update rate is an index to judge the quality of simulation software. Therefore, the establishment of high quality of Co-based alloy thermodynamic and kinetic database is vital to the development of cobalt alloy.At present, the multicomponent alloy thermodynamic databases have been reported in the literature. However, the reports of related diffusion kinetic databases are still missing. The atomic mobility is the storage information of kinetic databases.The main purpose of this study is to establish the high quality diffusion kinetic database of Co-based alloys. Three ternary fcc Co-based alloys are chosen in this work, i.e. fcc Co-Cr-Ni, fcc Cu-Co-Fe, fcc Cu-Co-Ni. The procedures are as follows:Firstly, diffusion couples are prepared by hot-pressing; Secondly, diffusion profiles are explored by electron probe microanalysis (EPMA) technology along the direction of the diffusion; Thirdly, interdiffusion coefficients are determined at the junctions of diffusion paths, after which atomic mobilities are retrieved in DICTRA with the aid of related thermodynamic descriptions; Finally, in order to evaluate the reliability of dynamic database, simulation of diffusion profiles in diffusion couples is performed with related thermodynamic and atomic mobility information. This work contributes to the establishment of a general Co-based kinetic database for computational design of superalloys.