Thermodynamic And Diffusion Kinetic Studies Of Key Phases In The Co-Al-Fe-Ni System

Although Co based superalloys have low yield strength at high temperature,they exhibit excellent hot corrosion resistance and oxidation resistance,which make them more suitable for high temperature parts with long life and good thermal fatigue resistance.Screening alloy compositions and designing industrial processes have been effectively accelerated by computational techniques equipped with thermodynamic and kinetic databases of alloys.Therefore,the establishments of thermodynamic database and mobility database for the major constituting phase(fcc and A2)are of critical necessity,and thus the Co-Al-Fe-Ni system are successfully carried out by means of the CALPHAD approach in the present work.The main contents of present work can be summaried as follows:(1)All the thermodynamic data of the binary and ternary systems were extensively collected and evaluated.The phase equilibria and the thermochemical property(heat capacity)were investigated through diffusion couple method,equilibrated alloys and high-temperature calorimetry.Comprehensive assessments of the thermodynamic properties for the Co-Al-Fe and Ni-Al-Fe systems have been performed based on the experimental data.The assessed themodynamic parameters are self-consistence and can repeat all the reliable experiemental data.(2)All the diffusion kinetic data in fcc and bcc_A2 phases of the sub-systems and ternary system of Co-Al-Fe alloy were extensively collected and reviewewd.The diffusivities for the fcc and A2 phases were experimentally measured through diffusion couple method.On the basis of the thermodynamic parameters and experimental diffusivities for the fcc and A2 phases,the diffusion mobilities in fcc and A2 Co-Al-Fe alloys were established.(3)All the diffusion kinetic data of the sub-systems and ternary system were extensively collected and reviewewd.The diffusivities for the fcc phase were experimentally measured through diffusion couple method.On the basis of the thermodynamic parameters and experimental diffusivities for the fcc phase,the diffusion mobilities in fcc Ni-Al-Fe alloys were established.(4)Based on the available themodynamic database of subsystems,the database of Co-Al-Fe-Ni system has been constructed.The reliability of the database was subsequently verified through precious and present phase equilibia data.