纳米晶合金中微观结构演化的数值模拟——晶界偏聚、溶质拖曳与力学行为
Numerical modeling of microstructure evolution in nanocrystalline alloys - grain boundary segregation, solute drag and mechanics
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中文总结 AI 辅助
本文提出一种三维有限应变相场有限元框架，统一模拟纳米晶合金的晶界偏聚、溶质析出及力学相互作用，为稳定晶粒尺寸提供数值工具，验证了框架适用性并解释相关效应。
中文摘要 AI 辅助
纳米晶（NC）合金作为结构合金具有广阔应用前景，其力学性能优于传统粗晶微晶合金。金属合金的强度与晶粒尺寸相关，经典霍尔-佩奇关系表明，金属强度随平均晶粒尺寸从微米级减小至纳米级（约20nm）而提升，若晶粒尺寸进一步减小，强度会下降，因此多数金属存在可获得最大强度的最优平均晶粒尺寸范围。在纳米晶合金领域，将晶粒尺寸稳定在该最优范围是合成的主要挑战之一。由于需要纳米级平均晶粒尺寸，合金合成过程中会利用晶界（GB）溶质偏聚和溶质析出等现象抑制晶粒长大。对晶界-溶质相互作用及受机械载荷作用下这些稳定化晶界演化进行数值模拟，是纳米晶合金领域的重要研究方向。为丰富该领域现有的数值模拟模型，本文提出一种基于相场方法的数值框架，用于模拟晶界偏聚、溶质析出以及外载荷对纳米晶合金的影响。尽管已有研究对其中部分效应进行了单独建模，但文献中尚未涉及溶质与晶界偏聚及力学相互作用的统一处理。本文提出一种用于模拟晶粒演化和微观结构稳定化的三维有限应变相场有限元（FEM）模型，除模型构建外，还通过多个案例研究验证了该框架的适用性，并基于晶界能量演化提供了热力学和动力学依据，以解释溶质拖曳、晶界钉扎和机械变形的效应。
英文摘要
Nanocrystalline (NC) alloys hold much promise as structural alloys due to their superior mechanical properties over traditional coarser grained microcrystalline alloys. Strength of metallic alloys is related to the underlying grain size - as represented by the classical Hall-Petch relation. Generally, a metals strength increases with decreasing mean grain size from the micrometer scale to the nanometer scale, until about a mean size of 20 nm. Any further decrease of grain size results in decreasing strength. Thus, there is an optimal range of mean grain size for most metals about which maximum material strength can be obtained. In the context of NC alloys, stabilization of the grain size in this optimal range is one of the primary synthesis challenges. Since nm-scale mean grain sizes are desired, phenomena like GB solute segregation and solute precipitation are utilized during alloy synthesis to mitigate grain growth. Numerical modeling the phenomena of GB-solute interactions and the evolution of these stabilized GBs under mechanical load are of immense interest to the NC alloy community. To enrich the numerical modeling formulations available in this space, we present here a phase-field method based numerical framework to model GB segregation, solute precipitation and effect of external loading on NC alloys. While some of these effects have been modeled in isolation, a unified treatment of the solute and GB segregation with mechanics interactions has not be considered in the literature. We present a 3D FEM finite-strain phase-field formulation for modeling grain evolution and microstructure stabilization. Beyond the formulation, various case studies demonstrate the applicability of this framework. Further, thermodynamic and kinetic arguments are provided based on the evolution of GB energy to explain the effects of solute drag, GB pinning and mechanical deformation.
