Phase Field Method And Kinetics Mechanism For Spinodal Decomposition Of Fe-Cr Alloys

Fe-Cr alloy has excellent c orrosion resistance,radiation resistance and high-temperature mechanical properties.The spinodal decomposition process of Fe-Cr alloy plays a decisive role in its microstructure and determines its final comprehensive properties.It is difficult to observe directly by experimental means.In this paper,the phase field method is selected to study the spinodal decomposition process of Fe-Cr alloy,and effects different factors(temperature,strain and third elements)on the spinodal decomposition process of Fe-40%Cr,its dynamic mechanism.(1)Temperature has the most direct effect on the spinodal decomposition of Fe Cr alloy.Based on the non-isothermal phase field model of binary alloy,the evolution process of spinodal microstructure morphology,volume,quantity and concentration of Fe-40%Cr alloy at different temperatures was studied.The results show that the Cr-rich droplets in the initial spinodal decomposition are densely distributed under different aging time.During the aging process,the Cr-rich droplets in Fe-Cr alloy are disorderly combined and have no clear orientation;At different temperatures and aging times,the number of Cr-rich droplets is inversely proportional to the diameter;The temperature gradient affects the solute stratification phenomenon in the spinodal decomposition process.When the temperature is lower than 750k,the solute stratification cannot be formed.With the increase of the temperature gradient,different stratification modes appear.The stratification with small temperature gradient is arched and protrudes to the low temperature zone.With the increase of the temperature gradient,the radian of the Cr-rich droplets gradually increases,and the appearance of the Cr droplets decreases with the increase of the droplet size.All solute stratification occurs in a specific temperature range(750-760k),and the stratification area gradually decreases with the increase of temperature gradient Δt.(2)Strain is an important factor affecting the spinodal decomposition process of Fe-Cr alloy.The spinodal decomposition process of Fe-40%Cr alloy under different stress conditions was studied.The simulation results show that under the action of strain,the process of spinodal decomposition will be further accelerated with induced strains;The greater the strain,the greater the merger and migration rate of Cr-rich droplets decomposed by spinodal.However,in the early stage of spinodal decomposition,the strain has little effect on the evolution of morphology.At this time,the microstructure of Cr-rich phase is labyrinth.Therefore,in practice,the microstructure of spinodal decomposition can be changed by applying different strains,so as to strengthen the material properties.(3)Adding the third component is an effective means to regulate the spinodal decomposition process of Fe-Cr alloy.The phase field method was used to simulate the spinodal decomposition process of Fe-40%Cr-5%Mo alloy,and the distribution characteristics of spinodal microstructure morphology,size and composition at different temperatures were studied.The results show that the addition of Mo will change the microstructure of the alloy.In Fe-Cr-Mo ternary alloy,there is a certain correlation between the concentration trend of Cr-rich phase and Mo-rich phase.The concentration of Mo-rich phase has a special shape,and its frequency and distance have a specific relationship with Cr concentration:the aggregation of Cr-rich phase drives the aggregation of Mo-rich phase,it will inhibit the agglomeration of Morich phase,resulting in the bifurcation of Mo Concentration at the peak of Cr concentration,which is lower than the peak of Mo concentration.