GOALI: Atomic Scale Modeling and Experimental Characterization of Non-Basal Deformation Modes in Mg Alloys

技术摘要：该项目将为通过选择性合金化设计具有良好强度和塑性组合的镁合金的定量和系统方法提供科学依据。该方法基于非基本形变模式的电子结构计算，包括c-a滑移和孪生，包括对合金化引起的化学效应的精确计算，并结合实验观察和计算预测的验证。用从头算和原子模拟的方法研究了(I)拉伸孪晶形核和合金促进孪晶形核和长大的机制(Ii)Mg中c_a位错的核心结构和迁移率(Iii)合金化对c_a位错结构和集体行为的影响。采用常规的透射电子显微镜，包括强场和弱束技术，对变形后的镁合金单晶和二元镁合金进行研究，以了解在特定加载形式下，化学作用对基于位错的变形响应的影响。这将为计算提供连接。此外，位错核结构的像差校正高分辨率电子显微镜将使计算结果更直接地联系在一起。这些实验和计算将提供对镁合金非基本变形的全面了解，化学对其相对易感性的影响，以及实现微观组织指导和科学信息的合金设计的途径。非技术摘要：镁和镁基合金的高强度/重量比使它们成为交通运输部门的优秀候选者，特别是专注于生产更轻、更省油的汽车的汽车工业。然而，有限的室温成形性(例如，通过在模具中成形来生产有用的形状所需的特征)限制了镁合金的广泛使用。在高温下成型增加了成本，降低了材料的竞争力。成形性与塑性变形的容易程度有关，这种现象是由称为滑移和/或孪生的原子水平过程促进的。本质上，这些原子水平的机制是材料对外力的反应，这些机制使材料发生永久的宏观形状变化，称为塑性变形。塑性变形的困难会导致另一种不受欢迎的反应，即过早失效/断裂。对于镁合金，有限的成形性与各向异性塑性变形有关。这意味着正在成形的板材在某些方向上很容易塑性变形，而在另一些方向上则不容易。这种各向异性的原因在于引发某些形式的塑性变形所需的应力(或力)的强烈差异，而不是其他形式的塑性变形，这是这种合金系统的特征。这个项目的重点是通过计算和实验相结合的方法来确定合金元素，以减少这些变形模式之间的临界应力差，从而促进各向同性塑性变形，从而改善室温成形性能。

Technical Abstract: This project will provide a scientific basis for a quantitative and systematic approach to design Magnesium alloys with favorable combinations of strength and ductility through selective alloying. The approach is based on electronic-structure calculations of non-basal deformation modes including c+a slip and twinning including accurately accounting for chemistry effects due to alloying coupled with experimental observation and verification of computational predictions. Ab initio and atomistic simulations will be done to investigate (i) Mechanisms for tension twin nucleation and alloys that promote nucleation and growth of twins (ii) the core structures and mobility of c+a dislocations in Mg (iii) effects of alloying on the structure and collective behavior of c+a dislocations. Conventional transmission electron microscopy including bright field, and weak beam techniques will be conducted on deformed single crystal of Mg and binary Mg alloys to understand the effect of chemistry on c+a dislocations -based deformation response for specific forms of loading. This will provide connections to computations. Furthermore, aberration-corrected high resolution electron microscopy of dislocation core structures will enable a more direct connection with results from computations. The experiments and computations together will provide a comprehensive understanding of non-basal deformation in Mg alloys, the effect of chemistry on its relative ease, and a pathway to microstructurally-guided and scientifically-informed alloy design.Non-technical Abstract: The high strength-to-weight ratio of magnesium and magnesium-based alloys makes them excellent candidates for the transportation sector and in particular, the automotive industry that is focused on producing lighter-weight, more fuel-efficient vehicles. However, limited room temperature formability (a feature required to produce useful shapes by forming in a die for example) has prohibited the widespread use of Mg alloys. Forming at elevated temperatures adds cost and makes the material less competitive. Formability is related to the ease of plastic deformation, a phenomenon that is facilitated by atomic level processes called slip and/or twinning. In essence, these atomic level mechanisms are the material's response to application of external forces and these mechanisms enable permanent macroscopic shape change in a material, referred to as plastic deformation. Difficulty in plastic deformation encourages an alternate undesirable response which is premature failure/fracture. In the case of magnesium alloys, the limited formability is related to anisotropic plastic deformation. This means plastic deformation is easy in some directions of the sheet that is being formed but not in others. The cause of this anisotropy lies in the strong differentials in stress (or force) needed to trigger some forms of plastic deformation as opposed to others, a characteristic of this alloy system. This project is focused on identifying alloying elements using a combination of computations and experiments that can reduce the critical stress differential between these deformation modes to facilitate isotropic plastic deformation and thereby improve room temperature formability.