Shear Viscosity of Liquid metals and alloys: Experiments and Atomic Characterization.

液态金属和合金的剪切粘度：实验和原子表征。

• 批准号: RGPIN-2014-06226
• 负责人: Shankar, Sumanth
• 金额: $ 2.11万
• 依托单位: McMaster University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=664866
• 关键词: Shear; Viscosity; Liquid; metals; alloys

The main objective of this study is to evaluate, characterize and quantify the flow behavior (shear stress as a function of shear rate) and shear viscosity of liquid metals and alloys that hold both academic and commercial significance. The research involves three interacting themes carried out in tandem: rheological experiments, atomic structure characterization through diffraction experiments and modeling through molecular dynamics and first principle formulations. The successful completion of this initiative and characterization of the flow behavior of liquid metals and alloys will have significant and far reaching impact in several areas of fundamental and applied materials science: casting (direct chill, continuous and near net shaped), joining (welding, soldering and brazing), single crystal growth, zone-refining and metal matrix composite processing to name a few. The design of many advanced manufacturing processes involving liquid metals and alloys requires a comprehensive understanding of transport properties in the liquid phases (such as the shear viscosity and associated relaxation time). These transport properties depend intimately on the microscopic structure and atomic composition of these liquids and our knowledge of this correlation is quite limited at present. While phenomenological models, either entirely empirical, or based on certain approximations of the microscopic processes involved in liquid transport have been used to predict transport phenomena in liquids, the gap between experiments and these models remains quite large. Our recent exploratory experiments and publications demonstrate that contrary to conventional wisdom, a wide variety of liquid metals and alloys exhibit non-Newtonian behavior, which are more pronounced at low shear rate regimes; this behavior is attributed to a transition in the governing mechanism from the resistance of the metallic bonding to shear, to momentum transfer between atom layers with increasing strain rate. At low shear rates the resistance offered to the flow of these liquids from the strong atomic bonds existing in the short range atomic order of the liquid structure dominates while at higher shear rates, the momentum transfer between atomic layers dominates the flow mechanism. This work motivates us to examine the fundamental mechanisms governing flow behavior in liquid metals and alloys through rigorous experiments, and atomistic structure evaluation and simulations, with a view to correlate and quantify the shear viscosity and the impact of liquid atomic structure on the same. Currently, our research group has the only high temperature rheometer in the North America, capable of evaluating rheological properties of liquids with a maximum temperature of about 1873 K in an environment chamber; acquired through our recent partnership with the Switzerland rheology equipment manufacturer, Anton Paar. Pure liquid metals and alloys of commercial interests such as Fe, steel, Si, Al alloys, Mg alloys, Cu alloy and Pb free solder alloys would be used as materials for rheological characterization (shear stress as a function of shear rate) with the high temperature rheometer. Diffraction experiments with both the Neutron and Synchrotron beam sources will evaluate structure information of liquid metals under controlled applied shear. Non-equilibrium molecular dynamics simulations using the popular molecular dynamics software packages, including VASP and LAMMPS will be formulated; attention will be restricted to determining and validating shear viscosity in pure liquid metals and simple binary alloys, and interatomic potentials appropriate for a study of shear viscosity will be employed. Through this study, we will gain useful insights into the physics governing this behavior.

这项研究的主要目的是评估，表征和量化流动行为（剪切应力随剪切速率的函数）以及具有学术和商业意义的液体金属和合金的剪切粘度。 该研究涉及在串联中进行的三个相互作用的主题：流变实验，通过衍射实验表征原子结构，并通过分子动力学和第一原理制定进行建模。 这项计划的成功完成和液体金属和合金的流动行为的表征将在基本和应用材料科学的多个领域具有重大且遥远的影响：铸造（直接寒意，连续和近乎净形状），连接（焊接，焊接，焊接和大型），单晶生长，区域培养和金属矩阵组合材料的加工，并将其命名为几个。许多涉及液体金属和合金的高级制造工艺的设计需要对液相（例如剪切粘度和相关放松时间）的运输特性进行全面了解。 这些运输特性密切取决于这些液体的显微镜结构和原子组成，目前我们对这种相关性的了解非常有限。尽管现象学模型是完全经验的，要么基于与液体转运有关的微观过程的某些近似值来预测液体中的转运现象，但实验与这些模型之间的差距仍然很大。 我们最近的探索性实验和出版物表明，与传统智慧相反，各种液体金属和合金表现出非牛顿的行为，在低剪切速率方案下更为明显。该行为归因于管理机制从金属键到剪切的电阻到剪切的过渡，到应变速率增加的原子层之间的动量转移。在低剪切速率下，从液体结构的短范围原子序中存在的这些液体流动的电阻占主导地位，而剪切速率则以较高的速率，原子层之间的动量转移主导了流动机制。这项工作促使我们通过严格的实验以及原子结构评估和仿真来检查液体金属和合金中流动行为的基本机制，以期将剪切粘度以及液体原子结构的影响相关联。 目前，我们的研究小组是北美唯一的高温流变仪，能够评估环境室中最高温度约为1873 K的液体的流变特性；通过我们最近与瑞士流变设备制造商安东·帕尔（Anton Paar）合作而获得的。 纯液体金属和商业利益的合金，例如Fe，Steel，Si，Al合金，MG合金，Cu合金和PB无焊料合金，将用作高温休闲计的流变学表征（剪切应力作为剪切速率）的材料。中子和同步束源的衍射实验将评估受控施加剪切液的液体金属的结构信息。使用流行的分子动力学软件包，包括VASP和LAMMP的非平衡分子动力学模拟，将制定；注意将限于确定和验证纯液体金属和简单二元合金的剪切粘度，以及适合于剪切粘度研究的原子间潜力。 通过这项研究，我们将获得有关这种行为的物理学的有用见解。