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

技术性：金属间合金由于其特殊的物理性能，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具有较低的延展性。最近发现了一类具有明显多晶延展性的全有序金属间化合物。例如，在室温下，YAg在实验室空气中的拉伸伸长率大于20%。对这种令人惊讶的行为的科学解释仍有待阐明，并将进行研究。新一类的延展性金属间化合物包括几十种化学计量线化合物，由稀土元素(R)和金属(M)组成，来自2或8-13族。虽然通常认为多晶延展性需要5个独立的滑移系统（von Mises条件），但对延展性RM化合物进行的单晶痕量分析只提供了3个独立的滑移系统。该研究将确定这些选择的合金如何维持延性塑性流动，同时明显违反冯米塞斯条件。晶体织构演化和塑性各向异性的多晶塑性模拟将用于预测维持塑性流动的变形机制。描述位错滑移和潜在的机械孪晶和马氏体相变的晶粒级机制的参数将通过实验获得的建模数据得到。原位中子衍射将用于直接检查孪晶或应力诱导相变的证据。载荷作用下的内部应变发展的衍射测量也将提供有关位错滑移机制的见解。透射电子显微镜（TEM）将用于探索位错微观结构的细节，如层错和反相边界。计划中的TEM实验还包括原位应变，以确定位错运动的源机制和动力学。非技术：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事业的机遇和挑战。教师暑期研究经验（RET）计划将使农村学校的教师接触到支撑材料科学与工程的加工-结构-属性范式。将进行演示，向学生介绍金属间合金的迷人特性。其中一些演示将用于加强本科材料科学和工程课程，而其他演示将在RET参与者教室和工程开放日活动中呈现给大学预科学生。

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.