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

非技术描述：金属玻璃是一种具有随机、非结晶结构的高强度金属合金。像所有的玻璃一样，它们的行为就像一种冻结的液体，其流动特性取决于它的粘度，或流动阻力，它随温度的变化而变化。了解流动如何随温度变化是解开金属玻璃底层结构背后的物理原理，以及了解其性质如何影响加工以及如何受加工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，玻璃像粘稠的液体一样流动，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状态的粘度，但迄今为止还没有方法可以测量浓液体状态的粘度。本研究的重点是采用新开发的方法，通过快速加热玻璃，同时测量其弹性响应来测量粘稠液体的粘度。收集的数据将用于确定控制流动的基本参数，开发和完善描述流动行为的适当模型，并改进创造可行商业产品所需的处理技术。这项合作努力将得到加州州立大学北岭分校和加州理工学院的教师和研究生的支持。研究生将指导代表性不足的暑期高中和大学实习生，扩大他们在专业社区的代表性，并激励他们追求STEM职业。技术描述：本提案描述了跨学科和合作研究，解决了大块金属玻璃合金（bmg）流变特性的明显数据缺口。bmg具有出色的硬度、韧性、强度和加工性，有望将金属的强度与塑料加工的便捷性相结合，并具有节能、环保的制造潜力。在过冷液体（SCL）区域，玻璃化转变温度和结晶温度之间存在流变学数据的差距。这些数据对于推进玻璃液体理论至关重要，并直接影响可加工性。我们建议使用欧姆加热驱动的快速温度漂移（快速放电成形，RDF）来测量该范围内一系列金属玻璃成分的粘度和其他热力学性质。试样在载荷作用下的高速随时间变形测量将用于确定粘度随温度的变化。在单独的实验中，将利用超声脉冲回波技术，结合高速红外热分析法，测量弹性剪切波速随温度的变化。数据将被纳入现有的玻璃流变学模型，并根据需要开发新的模型。通过这些研究获得的知识将应用于金属玻璃的概念验证加工，通过热塑性成形制造净形状物体，并进一步了解玻璃和玻璃金属的微观结构/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.