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延展性组合的镁合金的定量和系统方法提供科学依据。该方法是基于电子结构计算的非基础的变形模式，包括C+的滑移和孪晶，包括准确地占化学效应，由于合金化加上实验观察和验证的计算预测。从头算和原子模拟将进行调查（i）机制的张力孪晶形核和合金，促进孪晶的形核和生长（ii）的核心结构和移动的c+a位错在Mg（iii）合金化的影响的结构和集体行为的c + a位错。 将对变形的Mg单晶和二元Mg合金进行常规透射电子显微镜检查，包括明场和弱束技术，以了解化学对特定形式载荷的基于c+a位错的变形响应的影响。这将提供与计算的连接。此外，位错核心结构的像差校正的高分辨率电子显微镜将使更直接的连接与计算结果。实验和计算将提供对镁合金非基底变形的全面理解，化学对其相对容易性的影响，以及微观结构指导和科学信息合金设计的途径。非技术摘要：镁和镁基合金的高强度重量比使它们成为运输部门的优秀候选者，特别是，专注于生产重量更轻、更省油的汽车的汽车工业。然而，有限的室温可成形性（例如，通过在模具中成形来产生有用形状所需的特征）已经阻止了镁合金的广泛使用。 在高温下成型增加了成本，并使材料的竞争力降低。可成形性与塑性变形的容易性有关，塑性变形是一种通过称为滑移和/或孪生的原子级过程促进的现象。本质上，这些原子级机制是材料对施加外力的响应，并且这些机制使得材料能够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良反应，即过早失效/断裂。在镁合金的情况下，有限的可成形性与各向异性塑性变形有关。这意味着塑性变形在正在形成的片材的某些方向上是容易的，但在其他方向上不是。这种各向异性的原因在于触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，这是该合金系统的特征。 该项目的重点是使用计算和实验相结合的方法来识别合金元素，这些方法可以减少这些变形模式之间的临界应力差，以促进各向同性塑性变形，从而提高室温成形性。

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.