npj:相场模拟—尽“显”增材制造过程中的晶粒演化
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来自新加坡国立大学的闫文韬教授团队建立了一种三维相场模型(phase-field model, PFM),该模型综合考虑了粉末床融合过程中各因素对晶粒演化的影响,并采用GPU并行算法加速计算,全面地再现了多层多道PBF过程中各种晶粒演化,如熔池内的晶粒形核和生长(包括竞争生长),熔池边缘处的晶粒外延生长,熔道/熔层重叠区中的晶粒重熔和重新生长,以及热影响区的晶粒粗化。
在多层多道的粉末床融合模拟过程中,采用了集成建模思想:先利用离散单元模型模拟铺粉过程以获取粉床形貌,然后将粉床形貌导入介观尺度的热-流流动模型中,以预测PBF过程中的熔池变化和温度场变化,最后将温度场变化信息输入到相场模型中以模拟相应的晶粒演化。为实现晶粒演化的全方位模拟,在相场模型中1)耦合了晶粒异质形核模型,以模拟晶粒形核过程;2)考虑了晶界能各向异性和温度依赖的界面迁移率,以模拟竞争生长和热影响区的晶粒粗化;3)考虑了基板和粉末颗粒中的晶粒结构,以模拟熔池边缘处的晶粒外延生长。
在此基础上,系统地研究了多层多道PBF过程中典型晶粒形貌(如长条晶粒、“Z”型晶粒)的形成机理;分析了90o型旋转扫描策略对晶粒竞争生长及织构形成的影响;结合温度梯度和冷却速率讨论了不同熔融道内晶粒形核量的变化。此外,为了展示所建相场模型的潜在应用,初步模拟了纳米颗粒增强的金属基复合材料经选区熔化后的晶粒形貌。该研究所建的相场模型为更准确地预测粉末床融合过程的晶粒形貌提供了一种有效途径。
该文近期发表于npj Computational Materials 7: 56 (2021),英文标题与摘要如下,点击左下角“阅读原文”可以自由获取论文PDF。
Phase-field modeling of grain evolutions in additive manufacturing from nucleation, growth, to coarsening
Min Yang, Lu Wang & Wentao Yan
A three-dimensional phase-field model is developed to simulate grain evolutions during powder-bed-fusion (PBF) additive manufacturing, while the physically-informed temperature profile is implemented from a thermal-fluid flow model. The phase-field model incorporates a nucleation model based on classical nucleation theory, as well as the initial grain structures of powder particles and substrate. The grain evolutions during the three-layer three-track PBF process are comprehensively reproduced, including grain nucleation and growth in molten pools, epitaxial growth from powder particles, substrate and previous tracks, grain re-melting and re-growth in overlapping zones, and grain coarsening in heat-affected zones. A validation experiment has been carried out, showing that the simulation results are consistent with the experimental results in the molten pool and grain morphologies. Furthermore, the grain refinement by adding nanoparticles is preliminarily reproduced and compared against the experimental result in literature.
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