Understanding Dislocation Motion and Plasticity via First Principles Simulations Towards Manufacturing of High Ductility Magnesium Alloys

这项拨款支持促进韧性镁合金制造的基础研究。镁合金是最轻的结构材料，它们是汽车和航空航天应用的理想选择，在这些领域，提高能源效率变得越来越重要。然而，镁合金有限的室温延展性是镁合金广泛工程应用的主要挑战之一。镁在室温下的冷加工会导致开裂或断裂。因此，在高温下的热加工通常用于工业制造，但这增加了能源成本。为了提高延展性，在镁中加入了昂贵的稀土元素，但这是不可取的，因为稀土的高成本和不确定的可用性。该研究项目结合了计算和实验研究，以寻找廉价和容易获得的合金元素，用于制造具有优异延展性的新型镁合金。从这项工作中获得的结果使镁合金的低成本制造成为可能，这对美国的经济和环境产生了影响。该项目还在本科和研究生阶段促进综合计算材料工程原理的教育，并通过让妇女和代表性不足的少数民族参与科学、技术、工程和数学学科来促进多样性。镁的基面和棱柱面易位错滑移体系无法容纳沿六边形密排晶体结构c轴方向的应变分量。这导致镁在室温下的延展性有限。锥体c+a位错能够适应c轴应变，但其临界分解剪应力比棱柱形位错和基底位错高一到两个数量级。因此，在常规变形条件下，c+a位错密度不足以满足应变调节标准。该项目整合了第一性原理分层高通量筛选和实验研究，以确定能够降低Mg合金中c+a位错成核和滑动的能量屏障的合金元素。这是通过第一性原理模拟计算合金元素如何影响描述位错滑动的能垒的广义层错能的景观来实现的。确定合适的候选元素后，采用铸锭法合成镁合金。采用沟槽模压缩法制备细晶粒试样，进行拉伸和压缩试验，确定其力学性能。用透射电镜对位错结构进行了表征。该项目为开发新型高延展性镁合金提供了一种新的基于物理的策略，这种镁合金可以通过轧制、拉伸和冲压加工成有用形状的部件。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This grant supports fundamental research that facilitates manufacturing of ductile magnesium alloys. Magnesium alloys are the lightest structural materials and they are desirable for automotive and aerospace applications where improved energy efficiency becomes increasingly crucial. However, the limited room temperature ductility of magnesium alloys poses one of the major challenges to broad engineering application of these materials. Cold processing of magnesium at room temperature results in cracking or fracture. Hence, warm processing at elevated temperatures is typically used for industrial manufacturing, but this increases energy cost. To improve the ductility, expensive rare earth elements have been added to magnesium, but this is undesirable because of the high cost and uncertain availability of rare earths. This research project incorporates computational and experimental studies to search for inexpensive and readily available alloying elements for manufacturing new magnesium alloys with superior ductility. The results obtained from this work enables low-cost manufacturing of magnesium alloys which impacts the US economy and the environment. The project also promotes education of Integrated Computational Materials Engineering principles at undergraduate and graduate levels, as well as diversity by involving women and underrepresented minorities in disciplines of Science, Technology, Engineering and Math.Easy dislocation slip systems on the basal and prismatic planes in magnesium are unable to accommodate strain components along the c-axis of the hexagonal close-packed crystal structure. This leads to the limited ductility of magnesium at room temperature. The pyramidal c+a dislocations are able to accommodate c-axis strains, but their critical resolved shear stresses are one to two orders of magnitude higher than those of prismatic and basal dislocations. Consequently, under conventional deformation conditions, the density of c+a dislocations is insufficient to meet the criterion of strain accommodation. This project integrates first-principles hierarchical high-throughput-screening and experimental studies to identify alloying elements that are able to reduce the energy barrier to nucleation and glide of the c+a dislocations in Mg alloys. This is achieved by calculating through first principles simulations how alloying elements influence the landscape of generalized stacking fault energy which describes the energy barrier to dislocation glide. After suitable candidate elements are identified, magnesium alloys are synthesized by ingot casting. Channel die compression is carried out to fabricate samples with refined grains for tensile and compressive tests to determine their mechanical behavior. Dislocation structures are characterized by transmission electron microscopy. The project provides a new, physics-based strategy to develop novel high ductility magnesium alloys, which can be processed into components of useful shapes by rolling, drawing and stamping.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.