基于相场方法,模拟研究了Cu-20和40 at%Ag合金在等温时效过程中相分解与微观组织的演变.系统自由能中耦合了体化学能、浓度梯度能和共格错配应变能,化学自由能是直接利用相图热力学数据计算得到的,因此,计算的微结构变化与真实合金系统是相对应的.通过模拟,获得了合金的形态和浓度分布随时间、温度和组分的变化规律.模拟结果表明,对称合金(Cu-40at%Ag)分解和粗化的速度均高于相应的非对称合金,其相分离的早期阶段形成规则的、相互连接的微观形态.在Cu-20at% Ag合金中,沉淀相Ag经历了调幅分解和粗化过程,其形态呈立方状,沿[110]方向排列.
The phase decomposition and the microstructure evolution in Cu-20 and 40 at% Ag alloys during isothermal aging were simulated quantitatively based on the phase-field method.Contributions to the free energy of the system from bulk chemical mixing energy,concentration gradient energy and coherent misfit strain energy were incorporated.In the calculations,the chemical free energy used was obtained from the thermodynamic database of phase diagrams,therefore the calculated microstructure changes were related directly to the phase diagram of the real alloy system.The morphology and the composition profiles of the alloys were obtained as a function of time,temperature and component concentrations.The simulation results show that both the decomposing and coarsening rates of the symmetric alloy (Cu-40at% Ag) are higher than that corresponding to the asymmetric alloy.The early stages of phase separation in the symmetric alloy result in a regular and interconnected morphology.The Ag precipitations in Cu-20 at% Ag alloy during aging undergo a process including spinodal decomposition and coarsening,and change to a cubic shape aligned along the [100]direction.
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