Study Of ?/?' Microstructure Evolution In Some New Co-Al-based Superalloys Based On Phase-Field Simulation

With the rapid development of aviation industry,the current application temperature of Ni-based superalloys is close to its limit melting point and it is gradually unable to meet the future development needs.The development and design of a new ?'phase-strengthened Co-based superalloy with higher melting point,oxidation resistance and creep resistance is expected to break through the bottleneck and become a hot research topic in the aerospace field.Study of new Co-based superalloys has been extensively carried out in micro-calculations and macro-experiments,while the mesoscale phase-field simulation based on thermal/kinetic database and structure simulation is still insufficient.Therefore,it is of great significance to carry out research on the phase transformation mechanism and microstructure evolution of Co-based superalloys based on phase-field simulation.In this study,the evolution of?/?' two-phase structure during the aging process of some Co-Al-based superalloys was studied the evolution of microstructure and investigated the effect of the precipitation of the third phase(D019 phase and TCP phase)on the alloy structure stability through the experimental analysis and coupled thermal/kinetic database phase-field method simulation for the Co-Al-based superalloys with excellent performance.The main contents are as follows:(1)Experimental and phase-field methods were used to study the microstructure evolution and coarsening behavior of ?/?' two phases microstructure in Co-Al-W ternary alloys with different compositions and misfits.The results show that during the aging process,the ?' phase gradually coarsens into bricks or rectangles,and the Al element as the formation element of the ?' phase plays a key role in controlling the volume fraction of the ?' phase.The misfits rate ??0.53%has a great influence on the morphology of ?' particles,and it can suppress the coarsening process of ?' phase to a certain extent.(2)The phase-field method was used to study the microstructure evolution and coarsening behavior of ?/?' two phases microstructure in Co-Al-Ni ternary alloy at different compositions and temperatures.The results show that the precipitation process of ?' phase in Co-Al-Ni alloy has a certain similarity with Co-Al-W alloy,but the coarsening rate is about 1.5 times that of Co-Al-W alloy under the same conditions.Both Al and Ni elements have an effect on the volume fraction of the ?'phase,but the Al element is more sensitive.High temperature aging will result in lower supercool and precipitation driving force.The number of ?' phases precipitated at different temperatures will decrease with the increase of aging temperature and the coarsening rate will increase.(3)Experimental and phase-field methods were used to study the growth and coarsening kinetics of D019 and TCP phase during aging of Co-Al-W and Ni-Co-Al-W alloy.The results show that the composition of Al and W in Co-8.3Al-9.5W alloy will affect the driving force of D019 phase grain boundary precipitation,thus affecting the nucleation and growth rate of D019 phase.The precipitation of the D019phase leads to a decrease in the volume fraction of the ?' phase,and the coarsening rate k continuously decreases and changes.In the late aging of Ni-Co-Al-W,the coarsening process of ?' phase is intensified near the TCP phase,and the separation of the TCP phase occurs because the TCP phase with a smaller radius of curvature is exerted by the adjacent ?' phase caused by increased pressure Under the external stress conditions,alloying elements will diffuse directionally,leading to directional precipitation and coarsening of the ?' phase.