Fundamental Understanding of Deformation in High Entropy Structural Alloys

在工程应用中，金属合金化一直是产生相当强度以承受高服务负荷的方法。然而，抗断裂性（通常称为韧性），即在不发生灾难性断裂的情况下容忍裂缝的能力，往往随着强度的增加而降低。这在低温下尤其如此，因为低温下的韧性要低得多。另一个重要的衡量标准是延展性——材料承受较大伸长或挠度的能力——在提高常规合金的强度时也会受到影响。该奖项支持基础研究，为开发一种称为高熵合金（HEAs）的新型合金提供理解，这种合金具有高强度、高韧性和高延展性的能力。这些合金包含多种元素，但在小尺度上通过元素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。这些合金可以广泛应用于对美国经济至关重要的领域，包括机械、民用和材料科学领域。这项工作将对研究生进行教育，并通过在高中层面的推广，包括合金行为演示的暑期课程和用合金制作有用设备的实践活动，帮助扩大代表性不足的群体的参与。金属塑性变形的两种最重要的机制是滑移和孪生。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。它们的相互协同作用可以产生优越的性能。在这项工作中，潜在的新型高熵合金成分的第一性原理模拟将考虑滑移和双变形的能量景观，并开发包含连续体和原子效应的模型。然后，最有前途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双事件的发生，在低温下这些材料的巨大好处将被实现。实验还将考虑有限温度，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-亚微米尺度，以精确地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.