Elastic loading of metallic glass as a method to obtain defined enthalpy states

非技术总结本项目致力于一类新的金属材料，称为金属玻璃（MG）。与正常的金属合金相反，MG具有无序的原子结构，这使得它们更像是冻结的液体而不是晶体。这种结构上的变化带来了一系列优于传统工程金属（如钢）的优点。然而，MG的一个问题是它们的处理非常困难。玻璃态结构对各种工艺参数的敏感性导致了各种各样的结构和性能。这限制了MG在应用中的广泛使用，从而限制了对其特殊性质的利用。为了克服这个问题，PI使用了一种新的弹性加载协议，旨在引入一个定义的和可量化的结构状态，无论铸造历史。目标是实现结构参考状态，该结构参考状态随后可以通过热处理松弛到任何期望的状态及其相应的性质。如果成功的话，该项目因此提供了一种可逆的热机械加工方法，结束了MG铸造产生的不明确的结构状态和性能变化。这样的进步将显着促进这些新型合金在工程应用中的使用，例如，实现更节能的设备、新型消费品、高性能医疗设备或磁性部件。技术概述定义的热机械方案是针对特定微结构和特性的关键。这些知识用于日常工业操作中，以获得晶体金属材料的所需机械性能。改变无序金属材料（也称为金属玻璃（MG））的结构以及因此的机械性质由于缺乏明确的结构-性质关系而不那么直接。此外，在无定形MG中缺乏表观长度尺度使得很难识别给定的结构状态。因此，人们通常使用储存过量焓的量度来表征结构状态。在这个研究项目中，PI通过以下方式解决了这个缺点：i）通过弹性范围内的应力进行均匀再生，ii）通过演示不同长度尺度下的属性波动的空间相关长度如何直接量化给定的过量焓状态。这是通过在微米和纳米尺度上使用位点特异性表征方法来实现的。实验将揭示再生的饱和极限，PI从中构建一个关于如何准备定义明确和可量化的结构状态的热机械变形图。如果成功，这个研究项目引入了一个新的结构-性质的关系，定制性能的MG。这个奖项反映了NSF的法定使命，并已被认为是值得支持的，通过评估使用基金会的知识价值和更广泛的影响审查标准。

NON-TECHNICAL SUMMARYThis project is dedicated to a novel class of metallic materials that are called metallic glasses (MGs). Opposite to normal metallic alloys, MGs have a disordered atomic structure, which makes them more like a frozen liquid than a crystal. This change in structure brings a long a series of advantages over conventional engineering metals, such as steels. However, one problem with MGs is that their processing is very difficult. The sensitivity of the glassy structure to various processing parameters leads to a large variety of structures and therefore properties. This limits the widespread use of MGs in applications and thus the exploitation of their exceptional properties. In order to overcome this problem, the PI uses a novel route of elastic loading protocols that aim at introducing a defined and quantifiable structural state, irrespective of casting history. The goal is to achieve a structural reference state that subsequently can be relaxed via thermal processing to any desired state and its corresponding property. If successful, this project therefore provides a reversible thermo-mechanical processing method that puts an end to the ill-defined structural states and property variations originating from MG casting. Such an advance will significantly promote the usage of these novel alloys in engineering applications, enabling, for example, more energy efficient devices, novel consumer goods, high-performant medical devices, or magnetic components. TECHNICAL SUMMARYDefined thermo-mechanical protocols are a key to target specific microstructures and therefore properties. Such knowledge is used in daily industrial operations to obtain a desired mechanical performance of crystalline metallic materials. Modifying the structure, and therefore mechanical properties of disordered metallic materials, also known as metallic glasses (MGs), is much less straightforward due to the lack of well-defined structure-property relationships. Furthermore, the lack of apparent length scales in the amorphous MG makes it very difficult to identify a given structural state. Therefore, one normally uses the measure of stored excess enthalpy to characterize the structural state. In this research project, the PI addresses this shortcoming by i) homogeneous rejuvenation via stresses within the elastic regime, and ii) by demonstrating how spatial correlation lengths of property fluctuations at different length scales directly quantify a given excess enthalpy state. This is achieved by using site-specific characterization methods at the micron- and nanoscale. The experiments will reveal saturation limits of rejuvenation, from which the PI constructs a thermo-mechanical deformation map on how to prepare well-defined and quantifiable structural states. If successful, this research project introduces a novel structure-property relationship for tailoring properties of MGs.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.