再结晶和外力场下第二相析出的相场法模拟

在讨论相场法模拟基本方程的基础上，提出了晶界范围宽度的新概念，解释了相场模拟模型中有序化参数梯度范围的物理意义，论证了晶界范围不是晶界原子错排的宽度，而是界面能和界面元素偏析存在范围的观点.建立了一个模拟合金再结晶的相场模型，提出了一系列法则来获得模型中各参数的物理真实值，以AZ31镁合金为例，实现了再结晶过程晶粒长大的真实时间和空间的模拟，通过与试验数据的对比证明了模型的有效性.此外，还列举了相场法模拟Ti-25Al-10Nb合金中O相在外力场作用下析出过程的一系列有趣的新结果，讨论了外力场对第二相析出的重要影响和机理以及模拟结果对合金开发潜在的重要指导意义. 关键词： 相场法 再结晶 析出 外力场

Phase field simulation on recrystallization and secondary phase precipitation under strain field

General theory and formula of phase field simulation are discussed to as certain physical meanings of some phenomenological parameters in the basic model. A new concept of boundary range is suggested to explain the physical backgrounds of the phase order parameter gradients at grain boundary and the diffusion grain boundary, separately. It is argued that the boundary range is not the geometrical boundary width of atom disorder and generally believed to be within 3—4 atom sizes. However, the range has an independent boundary feature to represent the grain boundary energy distribution range in which the solute alloy atoms are segregated from interior grain. A model is established to simulate the realistic spatio-temporal microstructure evolution in recrystallization of a magnesium alloy by using the phase field approach. A set of rules has been proposed to determine the real physical value of all parameters in the model. The simulated results are shown to be in good agreement with reported measurements at the temperatures from 300 to 400 ℃ for up to 100 min. The effect of applied strains field on the microstructure produced during α₂ phase to O-phase （orthorhombic phase） transformation in Ti-25Al-10Nb alloy is finally studied by phase field simulation. The effects of strain direction on the volume fraction of O-phase and on the microstructure are investigated. It is also found that a full laminar microstructure can be formed when the applied strain is loaded along 〈1120〉 of α₂ phase with magnitude greater than a half of the stress-free transformation strain. The significance and the potential application of the new simulation discovery are discussed.