相场法研究Fe-Cu-Mn-Al合金富Cu相析出机制

Phase field study of effect of Al on Cu-rich precipitates in Fe-Cu-Mn-Al alloys

基于Ginzburg-Landau理论采用连续相场法模拟了Fe-15%Cu-3%Mn-x Al(质量分数x=1%, 3%, 5%)合金在873 K等温时效时纳米富Cu析出相沉淀机制及Al含量对富Cu相析出的阻碍效应.通过计算成分场变量和结构序参数,研究了富Cu析出相的形貌、颗粒密度、平均颗粒半径、生长和粗化动力学.研究结果表明:在时效早期阶段,纳米富Cu相通过失稳分解机制析出,由于原子扩散速率存在差异,从而形成以富Cu相为核心的核壳结构.随着时效时间延长,富Cu相析出物结构由体心立方转变为面心立方.其中Al和Mn原子在富Cu核外偏析形成Al/Mn簇,可以将其视为阻碍富Cu析出相形成的缓冲层;在沉淀过程中,随着Al含量的增大, Al/Mn金属间相促进了缓冲层的生长,阻碍富Cu析出相的生长和粗化.

Low carbon steel plays an important role in many applications due to its high strength.Its high strength comes from the strengthening effect of nano-Cu-rich phase precipitates.In order to effectively adjust the microstructure of Cu-rich phase precipitates and obtain Fe-Cu-based steel with the best properties by adding different alloying elements(Mn,Al),it is necessary to understand the precipitation process of Cu particles.In this paper,based on the Ginzburg-Landau theory,the previous phase field model is modified,and the continuous phase field method is used to simulate the precipitation mechanism of nanometer Cu-rich precipitates and the inhibiting of the effect of Al content on Cu-rich precipitates of Fe-15%Cu-3%Mn-xAl(x=1%,3%,5%mass fraction)alloy at 873 K isothermal aging.Combining with the free energy derived from thermodynamics database,the microstructure evolution corresponds to the real alloy system.By calculating the composition field variables and structural order parameters,the evolution of phase separation and precipitated phase morphology in aging process are simulated.Moreover,the influence law of morphology,quantity density,average particle radius,growth and coarsening of Cu-rich precipitated phase are discussed.The results show that in the early stage of aging process,the nano-Cu-rich phase precipitates through the spinodal decomposition mechanism,and is randomly distributed in the iron matrix.Furthermore,due to the difference in atomic diffusion rate,the core-shell structure with Cu-rich phase as a core is formed.With the aging time extending,the structure of Cu-rich phase precipitates changes from bcc to fcc.Because of the synergistic effect between Al and Cu,the diffusion of Cu is slowed down.Besides,with the Al and Mn atoms precipitating,Al/Mn clusters are segregated around the Cu-rich precipitates,forming the Al/Mn intermetallic core-shell structure,and gradually wrapping the Cu-rich phase uniformly.During the evolution of the precipitation stage,the Al/Mn clusters are isolated around the Cu-rich precipitation phase,forming a gradually uniform Al/Mn intermetallic phase core shell structure covering the Cu-rich phase,which is to hinder the buffer layer from forming in the precipitation stage of the reservoir.In addition,with the Al content increasing,the Al/Mn intermetallic phase promotes the growth of the buffer layer and hinders the Cu-rich precipitate phase from growing and coarsening.