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

本项目致力于研究一种被称为金属玻璃（mg）的新型金属材料。与普通金属合金不同的是，镁合金具有无序的原子结构，这使得它们更像冷冻的液体而不是晶体。这种结构上的变化带来了与传统工程金属（如钢）相比的一系列优势。然而，mg的一个问题是它们的处理非常困难。玻璃结构对各种加工参数的敏感性导致了各种各样的结构和性能。这限制了mgg在应用程序中的广泛使用，从而限制了其特殊特性的开发。为了克服这个问题，PI采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，而不考虑铸造历史。目标是实现一个结构参考状态，随后可以通过热加工放松到任何期望的状态及其相应的属性。如果成功，该项目因此提供了一种可逆的热机械加工方法，结束了由MG铸造引起的不明确的结构状态和性能变化。这一进展将极大地促进这些新型合金在工程应用中的应用，例如，使更节能的设备、新型消费品、高性能医疗设备或磁性元件成为可能。技术概述定义的热机械协议是目标特定微观结构和性能的关键。这些知识用于日常工业操作，以获得所需的结晶金属材料的机械性能。由于缺乏明确定义的结构-性能关系，改变无序金属材料（也称为金属玻璃（mg））的结构和机械性能要简单得多。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，人们通常使用储存的多余焓来表征结构状态。在本研究项目中，PI通过以下方式解决了这一缺点：i)通过弹性体系内的应力实现均匀再生；ii)通过展示不同长度尺度下属性波动的空间相关长度如何直接量化给定的过剩焓态。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。实验将揭示回复性的饱和极限，PI将据此构建关于如何制备定义良好且可量化的结构状态的热机械变形图。如果成功，该研究项目将引入一种新的结构-性能关系，用于定制mg的性能。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.