基于反常孪晶改善Mg-RE合金超高周疲劳和蠕变性能的机理研究

Mg and its alloys normally have poor high-cycle fatigue and creep properties. To solve these problems, suitable methods are in urgent need. In this project, Mg-Y and Mg-Gd-Y-Zn-Zr alloys are provided as research objects. For the first time, anomalous {10-12} twinning is proposed to synchronously improve the fatigue and creep properties through inhibiting cross-slip. Also, a novel method is designed for combining anomalous twinning with kinking to modify the geometrical morphology of long period stacking ordered (LPSO) structure, which is expected to improve creep resistance. High-cycle fatigue and creep tests will be performed on Mg-RE alloys with different amounts of anomalous twins and various LPSO structures. The microstructures will be observed by transmission electron microscope (TEM) and focused ion beam (FIB), and the crystallographical orientations will be examined by electron backscattered diffraction (EBSD). The forming conditions of anomalous twins and the effects of anomalous twins on crack propagation path will be explained in detail. The cooperative mechanisms of anomalous twins and kinks concerning their influence on high-cycle fatigue and creep properties will be revealed. We firmly believe that this project will spread the application field and enrich the twinning theory of Mg alloys. Moreover, this project will provide novel methods and feasible theoretical basis for the development of high-performance Mg alloys with ultra-long fatigue life and high creep resistance.

针对镁合金十分突出的抗高周疲劳性差和高温长时间强度不足的问题，本项目以Mg-Y和Mg-Gd-Y-Zn-Zr两种最具代表性的稀土镁合金为研究对象，首次提出利用反常孪晶抑制交滑移来改善疲劳和蠕变性能，以及通过反常孪晶和扭折带改变基面和LPSO相的几何形貌来提升高温长时间强度。对具有不同含量反常孪晶以及基面和LPSO相呈不同弯曲程度的样品分别进行疲劳和高温蠕变试验，采用先进的分析表征手段观察和分析不同阶段的微观组织。阐明反常孪晶的产生条件、影响因素及其对裂纹扩展路径的影响，弄清反常孪晶和扭折带对微观组织的协同调控作用以及对蠕变性能的影响规律，深入揭示反常孪晶和扭折带改善Mg-RE合金抗高周疲劳和高温抗蠕变性的微观机制。这一工作将进一步丰富和发展镁合金的安全服役与控制理论以及孪生理论，并为今后开发长疲劳寿命、高蠕变抗力的高性能镁合金提供新的思路和理论依据。

镁合金作为最轻的结构材料，在轨道交通和航空航天领域具有广阔的应用前景。然而，其耐蠕变、抗疲劳性差和高温长时间强度不足的问题严重制约了镁合金的大范围应用。本项目利用反常孪晶以及不同形貌的LPSO相抑制交滑移来改善镁合金疲劳和蠕变性能，重点研究了反常孪晶和扭折带与位错运动的相互作用，以及提升高温长时间强度的微观机理。取得的主要研究成果有：（1）阐明了反常孪晶的产生条件、影响因素及其对裂纹扩展路径的影响，弄清了反常孪晶对微观组织调控作用以及对蠕变性能的影响规律。确立了利用反常孪晶改善镁合金抗疲劳和高温抗蠕变性的新方法。（2）研究了初始织构，晶粒尺寸，RE元素含量对镁合金高温变形时的微观组织和蠕变性能的影响规律，得出了具体的镁合金抗蠕变强化手段，为开发高抗蠕变镁合金提供指导。（3）对镁合金进行预变形、预时效等处理，利用第二相、孪晶/扭折带与位错的交互作用来提升镁合金的高温抗蠕变性能，进一步阐明了第二相和孪晶/扭折带协同提升镁合金高温长时间强度的物理本质。本项目的工作将进一步丰富和发展镁合金的安全服役与控制理论以及孪生理论，并为今后开发长疲劳寿命、高蠕变抗力的高性能镁合金提供新的思路和理论依据。