CAREER: Understanding the Anomalous Ductility of Select B2 Intermetallic Compounds: Polycrystal Plasticity Modeling and Validation by In-Situ Diffraction Techniques

技术：金属间化合物合金因其特殊的物理性能而具有巨大的技术潜力。然而，绝大多数金属间化合物在室温下的延展性较低。最近发现了一类新的全有序金属间化合物，它具有显著的多晶延展性。例如，在实验室空气中，在室温下，YAG的拉伸伸长率超过20%。对这一令人惊讶的行为的科学解释仍有待阐明，并将进行研究。新类别的韧性金属间化合物包括数十种化学计量比的线状化合物，由2族或8-13族中的稀土元素(R)和金属(M)组成。虽然人们经常说多晶延性需要5个独立的滑移系统(冯·米塞斯条件)，但对延性RM化合物进行的单晶跟踪分析只提供了3个独立的系统。这项研究将确定这些选定的合金如何维持延性塑性流动，同时显然违反了冯·米塞斯的条件。多晶塑性模拟的晶体织构演化和塑性各向异性将被用来预测支持塑性流动的变形机制。描述位错滑移和潜在的机械孪生以及马氏体相变的晶级机制的参数将通过模拟实验数据获得。原位中子衍射将被用来直接检查孪晶或应力诱导相变的证据。对加载下的内部应变发展的衍射测量也将为位错滑移机制提供深入的了解。用透射电子显微镜研究了位错微结构的细节，如层错和反相界。计划中的透射电子显微镜实验还包括原位应变，以确定位错运动的来源、机制和动力学。非技术性：研究将影响许多领域，包括磁存储、超导、形状记忆合金、燃料电池和各种结构应用。研究还将使广大人口接触到科学和工程职业的机会和挑战。暑期教师研究体验(RET)计划将使农村学校的教师接触到支撑材料科学和工程的加工-结构-性能范式。将进行演示，向学生介绍金属间化合物合金的迷人特性。其中一些演示将被设计用于加强本科生的材料科学和工程课程，而另一些将在RET参与者的教室和工程学开放日活动中向大学预科学生展示。

TECHNICAL: Intermetallic alloys have tremendous technological potential due to their exceptional physical properties. However, the vast majority of intermetallics suffer from low ductility at room temperature. A new class of fully ordered intermetallics was recently discovered which exhibits significant polycrystalline ductility. For example, YAg exhibits greater than 20% elongation in tension at room temperature in laboratory air. A scientific explanation for this surprising behavior remains to be elucidated, and will be studied. The new class of the ductile intermetallics includes dozens of stoichiometric line compounds, comprised of a rare earth element (R) and a metal (M) from groups 2 or 8-13. While it is often stated that 5 independent slip systems are required for polycrystalline ductility (the von Mises condition), single crystal trace analyses performed on the ductile RM compounds provide only 3 independent systems. The research will determine how these select alloys sustain ductile plastic flow, while apparently violating the von Mises condition. Polycrystal plasticity simulation of crystallographic texture evolution and plastic anisotropy will be used to predict the deformation mechanisms that sustain plastic flow. Parameters describing the grain-level mechanisms of dislocation slip and potential mechanical twinning and martensitic phase transformations will be obtained by modeling data obtained experimentally. In-situ neutron diffraction will be used to directly examine evidence of twinning or stress-induced phase transformation. Diffraction measurement of the internal strain development under load would also provide insight regarding dislocation slip mechanism. Transmission electron microscopy (TEM) will be used to explore the details of the dislocation microstructure such as stacking faults and anti-phase boundaries. Planned TEM experiments also involve in-situ straining in order to determine the source mechanisms and kinetics of dislocation motion. NON-TECHNICAL: Research will impact a number of areas including magnetic storage, superconductivity, shape-memory alloys, fuel cells, and various structural applications. Research will also expose a broad segment of the population to the opportunities and challenges of a career in science and engineering. A summer research experience for teachers (RET) program will expose teachers from rural schools to the processing-structure-property paradigm underpinning materials science and engineering. Demonstrations will be developed to introduce students to the fascinating properties of intermetallic alloys. Some of these demonstrations will be designed to enhance undergraduate materials science and engineering classes, while others will be presented to pre-college students in the RET participants class rooms and at Engineering Open House events.