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近期文章
非线性和非共线相变应变路径对相场模拟马氏体形核和生长的影响
发布时间:2017-07-07

Effect of nonlinear and noncollinear transformation strain pathways in phase-field modeling of nucleation and growth during martensite transformation (非线性和非共线相变应变路径对相场模拟马氏体形核和生长的影响) 
Pengyang Zhao, Chen Shen, Ju Li & Yunzhi Wang
npj Computational Materials 3, Article number: 19 (2017)
doi:10.1038/s41524-017-0022-2
Published online:10 May 2017
Abstract| Full Text | PDF OPEN

摘要: 固体内的结构和化学组分的不均一性(杂质及缺陷)会产生内在的弹性场并进一步影响微观组织的演化;对该领域的研究,相场微弹理论已经发挥了重大作用。然而,传统相场微弹性理论中通常采用的关于本征相变应变张量和序参数间的线性和/或共线耦合关系排除了许多如原子计算所揭示的非线性相变路径。本研究采用更为一般的非线性和非共线相变应变路径,以此扩展现有相场微弹性理论,从而允许引入更为复杂的相变路径;该方法提供了一种多尺度建模方案,可将原子机制与总体动力学关联起来,从而更好地描述固态相变。作为实例,本研究探讨了一个一般的立方到四方的马氏体相变。结果表明,非线性相变路径可以显著改变形核和生长速率,并改变临界晶核的构型和激活能。本研究还发现,对于纯剪切马氏体相变,取决于实际相变路径,晶核以及奥氏体/马氏体界面可产生非零的远场静水压,从而可与其它晶体缺陷(例如点缺陷和背景张力/压缩场)展示出较传统理论预期更为复杂的相互作用。本文还进一步讨论了新理论应用在有关奥氏体/马氏体界面处的空穴聚集和共格界面处偏析现象研究的可能性。 

Abstract: The phase-field microelasticity theory has exhibited great capacities in studying elasticity and its effects on microstructure evolution due to various structural and chemical non-uniformities (impurities and defects) in solids. However, the usually adopted linear and/or collinear coupling between eigen transformation strain tensors and order parameters in phase-field microelasticity have excluded many nonlinear transformation pathways that have been revealed in many atomistic calculations. Here we extend phase-field microelasticity by adopting general nonlinear and noncollinear eigen transformation strain paths, which allows for the incorporation of complex transformation pathways and provides a multiscale modeling scheme linking atomistic mechanisms with overall kinetics to better describe solid-state phase transformations. Our case study on a generic cubic to tetragonal martensitic transformation shows that nonlinear transformation pathways can significantly alter the nucleation and growth rates, as well as the configuration and activation energy of the critical nuclei. It is also found that for a pure-shear martensitic transformation, depending on the actual transformation pathway, the nuclei and austenite/martensite interfaces can have nonzero far-field hydrostatic stress and may thus interact with other crystalline defects such as point defects and/or background tension/compression field in a more profound way than what is expected from a linear transformation pathway. Further significance is discussed on the implication of vacancy clustering at austenite/martensite interfaces and segregation at coherent precipitate/matrix interfaces. 

Editorial Summary
Structural transformation: a less linear approach (结构转变建模:不太线性的方法) 

美国研究人员开发了一种给固体晶体结构复杂变化建模的方法。来自俄亥俄州立大学的王云志教授及其同事所建的模型,能更精确地描述马氏体转变晶体结构的重排。尽管之前使用的相场微弹性理论为这种结构演化成功建模,但如同人们在用原子模拟时就已关注的那样,现有模型并没有纳入更加复杂的非线性相变路径。现在王教授及其同事扩展了相场微弹性理论,纳入了这些复杂路径。他们的研究表明,当考虑非线性耦合时,马氏体相的临界晶核构型和激活能均与传统相场微弹性理论所描述的存在显著差异。该模型有望进一步用于了解金属和陶瓷的结构转变过程。 

A method for modeling complex changes in the crystal structures of solids is developed by researchers in the USA. Yunzhi Wang from the Ohio State University and his colleagues’ model provides a more accurate description of crystal structure rearrangement during a phase change known as martensitic transformation. Even though this structural evolution has be modeled successfully using the phase-field microelasticity theory, the existing models do not incorporate some the more complex nonlinear transformation pathways that have been seen when using atomistic simulations. Wang and co-workers now extended phase-field microelasticity theory to include these complex pathways. They show that configuration and activation energies of a critical nucleus of the martensitic phase differ significantly when such nonlinear coupling is considered. This model has applications to understanding structural transformations in metals and ceramics.

 
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