基于液固遗传性以调控固溶极限为导向的Mg合金成分设计研究

Adding a heterogeneous solute into the binary Mg alloy containing "high quality" solute in a targeted manner can regulate the solubility limit of the "high quality" solute and further optimize the mechanical properties of the alloy. However, there is still no regularity knowledge for the solubility limit regulation potency of solute combination. Therefore, this subject proposes the study on the composition design of Mg alloy aimed at regulating the solubility limit. Constructing the alloy structure model that accurately exhibits the interaction characteristics of solute combination is the primary prerequisite for establishing the determination rule of regulation potency. Corresponding to the prerequisite, this subject will explore the atomic occupancy mechanism of solute combination in multicomponent Mg alloy by adopting the first-principles methods based on the liquid-solid heredity. According to this mechanism, the alloy structure model will be constructed, which makes it possible to clarify the structural and energetic effect of solute combination in multicomponent Mg alloy concentrated on the lattice distortion of the host, solution ability of solute and structural stability of solid solution. Through preparing alloys containing the selected key solute combinations with the fixed composition proportion, the relationship between the solubility limits of the main solute element and the structural and energetic effects of the solute combinations can be analyzed to finally ascertain the predictive parameters for solubility limit and establish the determination rule of solubility limit regulation potency of solute combination. The results of this subject will provide a composition design method for optimizing the mechanical properties of Mg alloys, and develop the liquid-solid heredity theory of metal and alloy composition design theory beyond Hume-Rothery rules.

在含有“优质”溶质的二元Mg合金中有针对性地加入异类溶质，可以调控“优质”溶质的固溶极限，优化合金力学性能。但不同溶质组合的固溶极限调控效能尚缺乏规律性认识，因此，本课题提出了以调控固溶极限为导向的Mg合金成分设计研究。构建出准确呈现溶质组合相互作用特征的合金结构模型，是建立调控效能判定规则的首要前提。对应该前提，本课题采用第一性原理方法，基于液固遗传性，探索多元Mg合金中溶质组合的原子占位机制。依此构建结构模型，并关注于基体晶格畸变、溶质固溶能力及合金结构稳定性，阐明多元Mg合金中溶质组合的结构、能量效应。选取关键的溶质组合，以固定成分配比制备合金，分析主要溶质元素的固溶极限与溶质组合结构、能量效应间的关系，最终确定固溶极限预测参数，建立溶质组合的固溶极限调控效能判定规则。课题成果可为优化Mg合金力学性能提供成分设计方法，发展金属液固遗传性与Hume-Rothery规则合金成分设计理论。

通过第一性原理计算建立以调控固溶极限为导向的合金设计规则，可为加速新合金的研发提供有价值的理论支撑。但由于固溶体中溶质原子的分布具有随机性，难以构建出明确的固溶体结构模型，这也进而阻碍了该领域系统性研究。为此，本项目以Mg-RE-X合金为研究对象，开展了如下工作。依照液固遗传性的思路，研究溶质组合的原子占位机制，构建明确的固溶体结构模型。在此基础上，从晶胞和第一配位层两个层面，系统研究溶质组合的结构、能量效应。依据结构、能量效应随元素周期表的演变规律，实验测定关键性合金的固溶度，建立溶质组合的固溶极限调控效能判定规则。通过以上研究，本项目提出了两类能够准确呈现溶质间相互作用特征的Mg-RE-X固溶体结构模型，并最终建立了Mg-RE-X合金中X对RE固溶极限调控效能的判定规则如下：第一，若添加元素X可提升目标元素RE的固溶极限，X对晶格体积、内聚能的影响应与RE相反，且X的12配位团簇体积、嵌入能与完美团簇的数值关系应相反于RE的12配位团簇体积、嵌入能与完美团簇的数值关系，否则X将降低RE的固溶极限，且降低效能正相关于Mg-RE-X固溶体与纯Mg内聚能偏差的绝对值；第二，若添加元素X可提升目标元素RE的固溶极限，即便在X与RE形成溶质对的极端情况下，二者之间依然无法发生明显的电子转移，否则X将降低RE的固溶极限，且降低效能正相关于双体相互作用能；第三，规则一主导X可在基体中固溶的Mg-RE-X合金，规则二主导X难溶于基体的Mg-RE-X合金。本项目基于液固遗传性确定的固溶体模型可为探索合金中的复杂原子行为提供一种合理的简化途径。更重要的是，本项目首次将基于Hume-Rothery规则的合金设计理论范围由二元合金扩展到多元，并通过对固溶体结构和能量特征的规律性呈现，使设计规则更具指导价值。