梯度纳米结构对铝合金力学性能影响的多尺度研究

Aluminum alloys could get close to or above 1 GPa ultrahigh strength after severe plastic deformation (SPD). After SPD, the aluminum alloy is usually characterized by a linear deformation gradient nanoscale grain size, and accompanied by a large number of solute atoms segregate to the grain boundaries. The present project aims to reasonably constructing of four basic gradient nanostructured polycrystalline atomic structure models base on the structure data obtained from TEM and 3DAP for molecular dynamics simulations. Moreover, molecular dynamics combining with the first principle are used to calculate the interaction between solute atoms and dislocations. The obtained micro parameters from two methods are put into the prediction and optimization of phenomenological model for gradient nanostructured aluminum alloy. The research contents are as follows: (1) effects of different gradient nanostructures on mechanical properties of nanocrystalline aluminum matrix; (2) the interaction of gradient nanostructured aluminum matrix of solute atoms with dislocations and grain boundaries etc.; (3) prediction of macroscopic mechanical properties of gradient nanostructured aluminum alloy based on the microscopic parameters. With the completion of this project, the microstructure characteristics and the enhancement mechanism of the gradient nanostructure in the high performance aluminum alloy can be obtained, which lays a theoretical foundation for the research and development of the new generation of high performance aluminum alloy. The software for generating the gradient nano polycrystal atomic structure model will lay the foundation for the research of all kinds of gradient nanostructured materials.

采用大塑性变形技术加工的铝合金可获得接近甚至超过1GPa的超高强度，其结构特点是晶粒尺寸达到纳米级,晶粒存在线性的形变梯度以及溶质原子大量偏聚到晶界的现象。本项目拟基于TEM与3DAP微结构数据，合理构建四种基本的梯度分布纳米多晶原子结构模型并用于分子动力学模拟，同时结合第一性原理计算研究溶质原子与位错的相互作用，两者所得微观参数再集成到唯象模型进行梯度纳米多晶铝合金力学性能的预测和优化。研究内容如下：(1)不同梯度纳米结构对纳米多晶铝基体力学性能的影响；(2)梯度纳米多晶铝基体中溶质原子与位错和晶界等的相互作用；(3)基于计算所得微观参数预测梯度纳米多晶铝合金宏观力学性能。本项目的完成，将获得高性能铝合金中梯度纳米结构的微结构特征与增强机制，为新一代高性能铝合金的研发奠定理论基础。编制完成的生成梯度纳米多晶原子结构模型软件，将为各类梯度纳米结构材料的研究奠定基础。

本项目主要围绕梯度纳米多晶铝合金力学性能的预测和优化来进行研究。我们编写了基于Voronoi方法和基于晶体相场凝固模拟的生成梯度纳米多晶原子结构模型的计算机代码，并基于构建的梯度纳米多晶结构采用分子动力学模拟研究了梯度纳米多晶结构对铝合金力学性质的影响，发现不同梯度纳米原子结构弛豫后内部位错分布各有不同，剪切强度随其梯度值的增加而增大，而且梯度纳米多晶中由于大量位错存在，剪切运动过程中应力应变起始的弹性阶段和塑性阶段观测到大量位错运动以及位错在晶界塞积，位错释放应力小于位错塞积引起的应力增强。而随着应力的进一步提高，屈服阶段取向与滑移方向差异较大的晶粒内部高密度层错大量释放，部分梯度纳米多晶结构剪切加载后形成贯穿结构的剪切带，应力随应变增加而缓慢下降。我们进一步编写了可读入梯度纳米多晶介观结构并用于晶体塑性有限元模拟的UMAT子程序的计算机代码，并对不同初始晶粒取向下梯度纳米多晶结构模型和均匀结构模型的铝合金的单向拉伸过程和剪切过程的计算与分析。项目最后还通过材料参数与多晶结构参数的变化建立了铝合金力学性质的高通量多尺度计算流程。项目在SCI收录的国内外学术期刊上发表论文12篇，培养博士研究生2名，硕士研究生1名。