Fe-Cr二元合金微观组织演化的质量密度场耦合动力学Monte-Carlo模拟研究

Monte-Carlo simulation of mass density field coupled dynamics for microstructural evolution of Fe-Cr binary alloys

本文建立了一种全新的将动力学Monte-Carlo粒子模拟与基于归一化Gauss函数基组的质量密度场空间粗粒化模型耦合的杂化模拟算法.采用该杂化模拟算法,系统对比研究了4种Cr原子含量分别为12.8%,20.0%,30.0%和40.0%的Fe-Cr合金中Cr相在温度为673 K下的时效析出动力学机制,及其时效不同阶段微观组织形貌的演变规律.研究得出Fe-Cr(12.8%)合金富Cr相时效组织形貌呈现孤立颗粒状空间分布形态,时效机制属于形核-长大(NG)机制;对于Fe-Cr(30.0%)和Fe-Cr(40.0%),富Cr相时效形貌在形核-生长及熟化阶段均呈现为三维蠕虫状空间分布特征,时效机制属于条幅分解(SD)机制;对于Fe-Cr(20.0%)合金,其富Cr相组织演化特征介于NG和SD机制之间.研究进一步发现Cr原子短程序参量可用来分析富Cr相形核-生长阶段Fe-Cr合金原子尺度结构的演变,但对于时效熟化阶段微观结构组织变化不敏感.基于空间粗粒化后Fe-Cr合金微观组织形貌,进一步分析了4种Cr原子含量下Fe-Cr合金相变动力学参数如富Cr相体积分数、平均粒径及相颗粒数密度随时效时间演变.本文建立的质量密度场耦合动力学Monte-Carlo模拟方法,为开发多尺度算法模拟合金时效动力学机制及微观组织形貌演变提供了新的思路和研究基础.

The phase transformation kinetics and micro-structure evolutions of four different Fe-Cr binary alloys,i.e.Fe-Cr(12.8%),Fe-Cr(20.0%),Fe-Cr(30.0%)and Fe-Cr(40.0%)at 673 K,are investigated by using the kinetic Monte-Carlo simulation combined with spatial coarse-grained mass density field description.For all studied Fe-Cr alloys,it is found that the number density of Cr-rich precipitate undergoes a rather rapid increasing at the nucleation stage and then gradually decreases with the simulation time increasing in the coarsening stage during aging.Increasing the Cr concentration in Fe-Cr alloy can significantly reduce the duration of nucleation and the time interval between nucleation and coarsening.From the coarse-grained mass density field models of Cr-rich precipitates at different aging stages for the four Fe-Cr alloys,we discover that the Cr-rich phase shows the isolated spherical particle-like morphology for the aged Fe-Cr(12.8%)alloy,revealing the nucleation and growth(NG)mechanism.Meanwhile,the Cr-rich precipitates possess a characteristic three-dimensional interconnected microstructure,a signature of spinodal decomposition mechanism.Otherwise,the Cr-rich phase morphology in Fe-Cr(20.0%)exhibits the characteristics of both NG mechanism and SD mechanism.It is also found that the short-range order parameter of Cr atoms in Fe-Cr alloy is indeed very sensitive to the change of atomic structure at the early stage of aging or nucleation stage,which,however,is almost independent of the changing of morphology of Cr-precipitates in the later coarsening process.Finally,the phase transformation kinetics of Cr-rich precipitates during aging are analyzed by calculating the phase volume fraction,average diameter and number density,concluding that the Cr-rich phase growth kinetics in Fe-Cr(20.0%)alloy can be described by the well-known Lifshitz-Slyozov-Wagner law in the coarsening stage.However,the coarsening kinetics of Fe-Cr(12.8%),Fe-Cr(30.0%)and Fe-Cr(40.0%)alloys are not caused by the LSW mechanism.