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

这笔赠款支持促进延性镁合金制造的基础研究。镁合金是最轻的结构材料，在提高能源效率变得越来越重要的汽车和航空航天应用中是可取的。然而，镁合金有限的室温塑性是这些材料广泛工程应用的主要挑战之一。镁在室温下进行冷加工会导致开裂或断裂。因此，高温下的热加工通常用于工业制造，但这会增加能源成本。为了改善延展性，在镁中加入了昂贵的稀土元素，但这是不可取的，因为稀土的成本很高，而且可获得性不确定。这一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来制造具有优异延展性的新镁合金。这项工作的结果使镁合金的低成本制造成为可能，这对美国经济和环境造成了影响。该项目还促进了本科生和研究生的综合计算材料工程原理教育，并通过让女性和在科学、技术、工程和数学学科中代表性较低的少数民族参与进来，促进多样性。镁合金基面和棱柱面上的易位错滑移系统无法容纳沿六方密排晶体结构c轴的应变分量。这导致镁在室温下的延展性有限。锥形c+a位错能够容纳c轴应变，但其临界分辨剪应力比棱柱位错和基面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准则。该项目将第一性原理、分级高通量筛选和实验研究相结合，以确定能够降低镁合金中c+a位错形核和滑移的能垒的合金元素。这是通过第一性原理模拟计算合金元素对广义层错能的影响来实现的，广义层错能描述了位错滑移的势垒。在确定合适的候选元素后，采用铸锭法制备镁合金。通道模压是用来制备细晶的样品，用于拉伸和压缩试验，以确定其力学行为。用透射电子显微镜表征了位错结构。该项目提供了一种新的、基于物理的战略来开发新型高延性镁合金，可以通过轧制、拉伸和冲压将其加工成有用形状的部件。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.