Fundamental Understanding of Deformation in High Entropy Structural Alloys

在工程应用中，金属合金化已成为产生相当大的强度以承受高使用载荷的方法。 然而，抗断裂性（通常称为韧性），即耐受裂纹而不发生灾难性断裂的能力，通常在强度增加时受到损害。在韧性显著降低的低温下尤其如此。另一个重要的衡量标准，延展性-材料承受大的伸长或挠曲的能力-也会影响传统合金的强度。该奖项支持基础研究，以提供对一类称为高熵合金（HEAs）的新型合金开发的理解，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，但通过元素在小尺度上的相互作用获得强度，并且即使在非常低的温度下也避免了延展性的损失，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进行大规模部署，包括机械，民用和材料科学部门。这项工作将教育研究生，并通过在高中水平的推广活动，包括暑期项目与合金行为的演示和实践活动，使有用的设备与合金扩大参与代表性不足的群体。金属塑性变形中最重要的两个机制是滑移和孪生。在滑移变形和孪生变形同时发生的情况下，可以实现前所未有的应变硬化，从而获得优异的性能。它们的相互协同作用可产生上级性能。在这项工作中，潜在的新的高熵合金成分的第一原理模拟将考虑滑移和孪晶变形的能量景观，并开发包括连续和原子效应的模型。最有前途的合金将被制造和测试。实验方法，然后将开发来测量在低温下，这些材料的巨大好处将实现的滑移和孪生事件的发生。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）推进到亚晶粒-亚微米尺度，以精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.