Collaborative Research: Closing the Bulk Metallic Glass Data Gap in the Supercooled Region

非技术描述：金属玻璃是具有随机、非晶态结构的高强度金属合金。像所有玻璃一样，它们的行为就像冻结的液体，其流动特性由其粘度或流动阻力决定，后者随温度变化。了解流动如何随温度变化是解开金属玻璃潜在结构背后的物理基础的关键组成部分，也是了解其性质如何影响加工及其影响的关键组成部分。有三种不同的行为：在低温下，玻璃表现为固体；在中等温度下，玻璃像浓液体一样流动，而在高温下，玻璃完全熔化。通过现有的方法可以很容易地测量低温和高温区域的粘度，但到目前为止还没有可用的方法来测量稠液区域的粘度。这项研究的重点是使用新开发的方法来测量稠液的粘度，方法是在测量玻璃弹性响应的同时快速加热玻璃。收集的数据将用于确定控制流动的基本参数，开发和改进描述流动行为的适当模型，并改进创造可行的商业产品所需的加工技术。这一合作努力将得到加州州立大学、北岭大学和加州理工学院的教职员工和研究生的支持。研究生将指导未被充分代表的夏季高中和大学实习生，扩大他们在专业社区中的代表性，并激发他们追求STEM职业生涯。技术描述：该建议描述了针对大块金属玻璃合金(BMG)流变性能中明显的数据缺口进行的跨学科和协作研究。BMG具有优异的硬度、韧性、强度和加工性，有望将金属的强度与塑料加工的简易性相结合，并具有节能、环保制造的潜力。在过冷液(SCL)区，玻璃化转变温度和晶化温度之间存在着流变数据的差距。这些数据对推进玻璃态液体理论至关重要，并直接影响可加工性。我们建议使用欧姆加热(快速放电成形，RDF)驱动的快速温度漂移来测量一系列金属玻璃成分在此范围内的粘度和其他热力学性质。样品在载荷下的高速随时间变化的变形测量将被用来确定粘度随温度的变化。在单独的实验中，将使用超声脉冲回波技术，结合高速红外测温，测量弹性剪切波速度随温度的变化。数据将被纳入现有的玻璃流变学模型，并将根据需要开发新的模型。通过这些研究获得的知识的应用将应用于金属玻璃的概念验证加工，通过热塑性成形制造网状物体，以及进一步了解玻璃和玻璃金属中的微结构/加工/性能关系。

NON-TECHNICAL DESCRIPTION:Metallic glasses are high-strength metallic alloys that have a random, non-crystalline structure. Like all glasses, they behave like a frozen liquid with flow characteristics determined by its viscosity, or resistance to flow, which varies with temperature. Understanding how flow varies with temperature is a key component both to unlocking the physics behind the underlying structure of metallic glasses, and knowing how its properties influence, and are influenced by, processing. There are three different behaviors: At low temperature the glass behaves as a solid; at moderate temperature, in which the glass flows like a thick liquid, and at high temperature the glass is fully melted. Viscosity measurement of the low- and high-temperature regimes is readily accessible through existing methods, but to date no methods are available to measure viscosity in the thick liquid regime. The focus of this research is to employ newly developed methods to measure viscosity of the thick liquid by rapidly heating the glass while measuring their elastic response. The data collected will be used to identify the fundamental parameters that control flow, develop and refine appropriate models for describing flow behavior, and improve processing techniques need for creating viable commercial products. This collaborative effort will be supported by faculty and graduate students at California State University, Northridge, and California Institute of Technology. Graduate students will mentor underrepresented summer high school and college interns, expanding their representation in the professional community and exciting them to pursue STEM careers.TECHNICAL DESCRIPTION:This proposal describes interdisciplinary and collaborative research addressing a conspicuous data gap in the rheological properties of bulk metallic glass alloys (BMGs). BMGs, with their outstanding hardness, toughness, strength and processability, show promise to combine the strengths of metals with the ease of plastic processing, and the potential for energy efficient, environmentally clean manufacturing. The gap in the rheological data exists in the supercooled liquid (SCL) region, between the glass transition and the crystallization temperatures. This data is pivotal in advancing the theory of glassy liquids, and directly impacts processability. We propose to measure the viscosity, and other thermodynamic properties, of a series of metallic glass compositions in this range using rapid temperature excursions driven by ohmic heating (rapid discharge forming, RDF). High-speed time-dependent deformation measurements of a sample under load will be used to determine viscosity variation with temperature. In separate experiments, the ultrasonic pulse-echo technique, coupled with high-speed infrared pyrometry, will be used to measure the elastic shear wave velocity variation with temperature. Data will be incorporated in existing glass rheology models, and new models will be developed as required. Application of the knowledge gained through these studies will be applied to the proof-of-concept processing of metallic glasses, making net-shape objects through thermoplastic forming, and further understanding of the microstructure/processing/properties relationship in glasses and glassy metals.