| With the rapid development of the aviation industry,a new generation of turbine blade material that could operate at higher temperature is desired.Researchers discovered a new L12 ordered ?' phase Co3(Al,W)in the Co-Al-W system,and developed a new ?' phase-strengthened Co-based superalloys,this new type of Co-based superalloys not only has the advantages of traditional Co-based superalloys,it also has good high-temperature strength,and it is expected to become the next-generation superalloys.The research and development of new ?' phase-strengthened Co-based superalloys have become the current research hotspot.In addition,researchers have designed new ?' phase-strengthened Co-based superalloys based on the alloying of Co-Ti and Co-Ta systems,it is evident that the Co-X(X:Ti,Ta)alloys are the key system to develop new ?' phase-strengthened Co-based superalloys.Alloying will change the volume fraction of ?' phase and the misfit between ?/?' two-phase,both of them have a significant effect on morphology,particle size and coarsening behavior of ?' phase,thus influencing the properties of the Co-based superalloys.The phase field method which coupled with thermodynamic and kinetic database provides a new and effective way to quantitative simulate the evolution of microstructure in alloys.Therefore,it is necessary to study the microstructure evolution of Co-based superalloys,so as to provide a theoretical basis for the design of Co-based superalloys.This works combine experiment and phase field method to study the influence of aging temperature,composition and the misfit between ?/?' two-phase on the microstructure evolution of ?/?' two-phase in Co-X(X:Ti,Ta)alloys.The details of the results are as follows:(1)The microstructure evolution and coarsening behavior in the Co-Ti alloy with the ?' phase as precipitates were studied by the experiments and phase field simulations.The influence of temperature,composition and the misfit between ?/?' two-phase on the morphology,volume fraction,and coarsening rate of ?' phase were analyzed.The results show that the mechanisms of growth and coarsening of the ?' phase are mainly consist of the Ostwald ripening and the particles which have the same anti-phase domains merging with each other.With the increase of temperature,the coarsening rate of ?' particles increases.With the increase of Ti concentration,the coarsening rate of ?'particles decreases first and then increases.With the increase of the misfit between ?/?'two-phase,the coarsening rate of ?' particles and the proportion of rod-like shape ?'particles increase.(2)The microstructure evolution and coarsening behavior in the Co-Ti alloy with the ? phase as precipitates were studied by the experiments and phase field simulations.The influence of temperature,composition and the misfit between ?/?' two-phase on the morphology,mean particle radius and particle size distribution of ? phase were analyzed.The results show that the adjacent y particles are more likely to merge due to the absence of anti-phase domains.The coarsening rate of ? particles increases and the volume fraction of ? particles decreases with temperature increasing.The coarsening rate of ?particles reduces with the Ti concentration increasing.The morphology of y particles grows from near-spherical and square shape to rod-like shape with the misfit between?/?' two-phase increasing.(3)The influence of temperature,composition and the misfit between ?/?' two-phase on the microstructure,particle size distribution and coarsening rate of ?' phase in Co-Ta alloy have been investigated by phase-field method.The results show that the coarsening rate of ?' particles increases with temperature and the misfit between ?/?'two-phase increasing.With the increase of Ta concentration,the morphology of ?'particles changes into irregular-cuboidal shape,the coarsening rate of ? particles decreases first and then increases,the peak of PSDs becomes smaller and move to left side,and breadth of the PSDs becomes broaden. |
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