Fundamental Understanding of Deformation in High Entropy Structural Alloys

在工程应用中，金属的合金化一直是产生相当大的强度以承受高使用负荷的方法。然而，抗裂性(通常称为韧性)，即容忍裂缝而不发生灾难性断裂的能力，往往随着强度的增加而降低。在韧性明显较低的低温下尤其如此。另一个重要的衡量标准是延展性，也就是材料承受较大伸长或变形的能力，这也会影响到传统合金的强度。该奖项支持基础研究，为开发一种名为高熵合金(HEAs)的新型合金提供了解，这种合金具有高强度、高韧性和高延展性的能力。这些合金涉及多种元素，但通过元素在小范围内的相互作用获得强度，即使在非常低的温度下也可以避免延展性的损失，从而扩大了它们的潜在用途。这些合金可以在对美国经济至关重要的领域实现广泛部署，包括机械、民用和材料科学部门。这项工作将教育研究生，并通过在高中层面的推广，帮助未被充分代表的群体更广泛地参与，包括展示合金行为的暑期项目，以及用合金制造有用装置的动手活动。金属塑性变形的两个最重要的机制是滑移和孪生。在滑移变形和孪生变形可以同时发生的情况下，可以获得前所未有的应变硬化的特殊性能。它们的相互协同可以产生更好的性能。在这项工作中，潜在的新高熵合金成分的第一性原理模拟将考虑滑移和孪晶变形的能量景观，并发展包括连续和原子效应的模型。然后，最有希望的合金将被制造和测试。然后将开发实验方法来测量低温下滑移和孪生事件的发生，在那里将实现这些材料的巨大好处。这些实验还将考虑有限的温度，并旨在将数字图像相关方法(一种测量局部位移和应变的技术)提高到亚晶-亚微米尺度，以准确了解这些合金中的变形现象。

Alloying of metals has been the method of producing considerable strength to withstand high service loads in engineering applications. However, the resistance to fracture (often termed the toughness), i.e. the ability to tolerate cracks without catastrophic fracture, is often compromised upon increase in strength. This is especially true at low temperatures where toughness is substantially lower. Another important measure, the ductility - the ability of the material to sustain large elongations or deflections - also suffers upon raising the strength in conventional alloys. This award supports fundamental research to provide understanding towards the development of a new class of alloys called the high entropy alloys (HEAs) which have the capability of possessing both a high strength, high toughness, and high ductility. These alloys involve multiple elements but derive strength through interactions of elements at small scales, and circumvent the loss of ductility even at very low temperatures, broadening their potential use. These alloys can enable wide-scale deployment in areas critical to the US economy including mechanical, civil, and materials science sectors. The work will educate graduate students and also help broaden participation of underrepresented groups through outreach at the high school level, including summer programs with demonstrations of alloy behavior and hands-on activities making useful devices with alloys.Two of the most important mechanisms in plastic deformation of metals are slip and twinning. Exceptional properties can be achieved for cases where slip deformation and twinning deformation can occur simultaneously with unprecedented strain hardening. Their mutual synergism can produce superior properties. In this work, first principles simulations of potential new high entropy alloy compositions will consider the energy landscapes for slip and twin deformation, and develop models that encompass both continuum and atomistic effects. The most promising alloys will then be manufactured and tested. Experimental methodologies will then be developed to measure the onset of slip and twin events at low temperatures where the tremendous benefits of these materials will be realized. The experiments will also consider finite temperatures and aim to advance digital image correlation methods (a technique for measuring local displacements and strains) to subgrain-submicron scales to understand precisely the deformation phenomenon in these alloys.