[论文解读] Over the shear paradigm

Cyril Cayron|arXiv (Cornell University)|Jun 23, 2017

Microstructure and mechanical properties参考文献 102被引用 14

一句话总结

本文通过提出基于角度畸变的新框架，挑战了晶体学模型中长期存在的剪切范式（如形变孪生和马氏体相变）——该框架在刚性球假设下，将原子轨迹、晶格畸变和原子重排建模为单一角度参数的解析函数，为简单剪切和位错介导机制提供了一种更具物理一致性的替代方案。

ABSTRACT

Deformation twinning and martensitic transformations are displacive transformations; they are defined by high speed collective displacements of the atoms, the existence of a parent/daughter orientation relationship, and plate or lath morphologies. The current crystallographic models of deformation twinning in metals are based on the 150 year-old concept of simple shear. For martensitic transformations, a generalized version of simple shear called invariant plane strain takes into account the volume change; it is associated with one or two simple shears in the phenomenological theory of martensitic crystallography built more than 60 years ago. As simple shears would involve unrealistic stresses, dislocation/disconnection-mediated versions of the usual crystallographic models of displacive transformations have been developed over the last decades. However, fundamental questions remain unsolved. How do the atoms move? How could dislocations be created and propagate in a coordinated way at the speed of sound? In order to solve these issues an approach that is not based on simple shear nor on dislocation/disconnection has been applied to different displacive transformations over the last years. It assumes that the atoms are hard-spheres, which permits for any specific orientation relationship to determine the atomics trajectories, the lattice distortion and shuffling (if required) as analytical functions of a unique angular parameter. The aim of the present paper is to give a brief historical review of the current models based on the shear concept and of their dislocation-mediated versions, and to introduce the new paradigm of angular distortion. Examples will be taken by using some recent publications. The possibilities offers by this approach in mechanics and thermodynamics are briefly discussed.

研究动机与目标

• 批判性评估经典剪切范式在建模形变孪生和马氏体相变时的局限性。
• 解决形变性相变中关于原子运动和位错动力学在超音速下的未解问题。
• 开发一种新的晶体学框架，避免依赖简单剪切或位错机制。
• 在刚性球约束下，基于单一角度参数，为原子轨迹和晶格畸变提供解析解。
• 为基于力学和热力学的形变性相变晶体学新范式奠定基础。

提出的方法

• 假设原子行为如同刚性硬球，以定义原子运动的几何约束。
• 推导出任意给定取向关系下，原子轨迹、晶格畸变和原子重排作为单一角度参数的解析函数。
• 将角度畸变模型应用于多种形变性相变，包括形变孪生和马氏体相变。
• 利用刚性球模型消除与简单剪切和位错介导机制相关的非物理应力。
• 将新模型整合到现有现象学框架中，以评估其与观测形态和取向关系的一致性。
• 将角度畸变方法与经典剪切模型及位错介导理论进行比较，突出其在物理合理性方面的优势。

实验结果

研究问题

• RQ1 如何在不依赖简单剪切概念的前提下，对形变性相变中的原子运动进行建模？
• RQ2 控制形变孪生和马氏体相变中原子轨迹的物理和几何约束是什么？
• RQ3 单一角度参数是否能完全描述与观测取向关系一致的晶格畸变和原子重排？
• RQ4 角度畸变模型如何解决位错在形变性相变中以声速运动的悖论？
• RQ5 用角度畸变框架取代剪切模型，其热力学和力学意义是什么？

主要发现

• 角度畸变模型为原子轨迹、晶格畸变和原子重排提供了基于单一角度参数的解析表达式，适用于任何取向关系。
• 该模型消除了与简单剪切相关的非物理高应力，提供了更真实的原子运动描述。
• 该方法仅通过几何约束即可解释形变孪生和马氏体相变中板条或透镜状形态的形成。
• 该方法与观测到的母相/子相取向关系一致，并为不同类型的形变性相变提供了统一框架。
• 该模型为理解形变性相变的力学与热力学提供了新途径，且无需引入位错介导机制。
• 该框架具有普适性，可广泛应用于各类材料和相变类型，如本文引用的近期文献所展示。