金属合金位错芯结构与力学响应的相场方法研究

As indicated by a lot of experiments, the strength and plastic property of metals are not only closely related to long-range elastic interaction between dislocations, but also dramatically influenced by the change in dislocation core structures. The latter issue, however, has been rarely concerned with in the existing theoretical researches due to its computational complexity. In view of this status, the plan of this proposal is to develop an improved phase-field model for dislocations, and perform systematical simulations for pattern evolution and mechanical response of complicated networks of dislocations with changeable core structures so as to lay down theoretical foundation for strengthening and roughening of metallic materials. The main routine of the research is as follows. Effects of solute atoms and strain rates on the interatomic potentials on gliding planes in typical metallic crystals are explored quantitatively based on atomic simulations. The results then are used to construct three-dimensional crystalline energy function which incorporates the solute and inertial effects. An improved three-dimensional phase-field model is formulated in the cross-scale framework of Peierls–Nabarro model. Through numerical computations, impacts of solute atoms and strain rates on the width and planar-nonplanar transmission of dislocation core structures are revealed, and pattern evolution and mechanical response of dislocation networks with changeable core structures in crystals exhibiting multiple slipping systems are clarified. The results of the research will provide a new method of simulation for large spatiotemporal scale evolution of complicated dislocation systems, and also lead to novel insights for understanding deformation mechanisms sensitive to the change of dislocation core structures.

实验表明，材料的强度与塑性性能不仅与位错间的长程弹性相互作用紧密相关，也受位错芯结构变化的强烈影响。然而，后一个方面因为计算上的复杂性在已有的理论研究中很少被涉及。鉴于这一状况，本项目拟发展改进的位错相场模型，系统模拟位错芯结构可变的复杂位错网络组态演化与力学响应，为金属材料的强韧化设计提供理论依据。项目的主要研究内容是，基于原子层次的模拟定量探索溶质原子浓度和应变率效应对典型晶体滑移层间势的影响，在此基础上构造计入上述影响的三维晶体能函数，并在广义的Peierls–Nabarro跨尺度框架下提出改进的三维位错相场模型，进而通过模拟揭示溶质原子和应变率效应对位错芯宽度、平面芯到非平面芯结构变化的影响，阐明多个滑移系统中计入位错芯结构变化的位错网络组态演化与力学响应。本项目结果将为复杂位错系统的大时空尺度演化提供新的模拟方法，也为位错芯结构变化敏感的材料形变机制的理解提供新的认识。

金属合金的强度与塑性性能不仅与位错-位错之间、位错与微结构之间复杂的长程弹性相互作用紧密相关，而且受位错芯结构变化和溶质原子扩散的强烈影响。传统的连续统位错模型没有综合考虑这些因素，而分子动力学模拟受时间和空间尺度的限制也难以提供全面的认识。本项目结合原子尺度计算的结果和连续相场动力学的思想，系统探索计及错芯结构变化和溶质原子扩散效应的复杂位错网络形成、相互作用和演化规律。主要成果包括：. 1.以辐照为背景通过分子动力学模拟揭示了体心立方铁铬合金中辐照诱导位错形核的微观机制以及铬浓度的影响；. 2.基于正则固溶体模型和第一性原理计算的伽马表面势发展了一种考虑溶质原子扩散的半共格界面位错的相场方法；. 3.运用数值模拟阐明了溶质原子偏析与界面位错网络耦合演化规律以及晶界扭转角和失配度对结构形成的调控作用；. 4.在广义Peierls–Nabarro模型的框架下通过模拟量化了单个位错穿越空洞和夹杂过程中芯结构变化及其产生的影响；. 5.受界面位错网络变形启发提出了一种利用含周期性向错网络的膜-基系统实现复杂材料表面形貌形成和调控的策略；. 6.由基于第一性原理层间势的相场动力学模拟发现了moiré超晶格中普遍存在的依赖于扭转角的最大弹性相互作用。. 本项目的结果可望为从位错芯结构出发预测、理解和设计金属材料的宏观力学性能提供有效的方法和模拟手段。