镁合金中长周期有序堆垛结构热力学模型及形核机制研究

含有长周期有序堆垛结构（LPSO）的稀土镁合金具有良好的强塑性及抗蠕变性能，被认为是最具有应用潜力的新型高性能镁合金。然而，LPSO相的形成机制及如何科学调控其析出尚不明确。本项目以Mg-Al-Y合金LPSO相为研究对象，结合实验测定和第一性原理计算方法，探究合金元素和温度对LPSO相原子占位的影响，对其进行热力学建模；结合实验测定的Mg-Al-Y体系平衡相图、固溶体相的摩尔体积及第一性原理计算数据，采用CALPHAD方法建立可靠的含LPSO相的Mg-Al-Y体系热力学和摩尔体积数据库。与此同时，通过引入hcp/fcc相变自由能、界面能及溶质原子偏聚化学能和弹性能，构建层错能热力学模型，获得层错能和LPSO相变驱动力与成分和温度之间的定量关系，进而阐明层错能对LPSO相析出的影响规律，建立LPSO相析出的热力学条件，为科学调控LPSO相的析出，设计新型高性能耐热镁合金提供理论依据。

The rare earth magnesium alloys containing the long period stacking ordered structure (LPSO) possess excellent strength, ductility and creep-resistance, which are considered to be the novel high performance Mg alloys with the most potential applications. However, the formation mechanism of the LPSO phase and the rational control of its precipitation have not been clarified. In the present project, the effect of alloying elements and temperature on the atomic occupancy of the LPSO phase in Mg-Al-Y alloys is firstly studied through the critical experimental investigation and ab initio calculations. By using the CALPHAD method, the LPSO phase is thermodynamically modelled. Then, the phase equilibria of the Mg-Al-Y system and molar volume of the solid solution phase are investigated experimentally and theoretically. The thermodynamic and molar volume modelling of the Mg-Al-Y system are performed and a reliable database for the system is established. Meanwhile, the thermodynamic model of the stacking fault energy is established through introducing the hcp/fcc phase transformation energy, interfacial energy, segregation chemical energy and segregation elastic energy, which could provide the composition- and temperature-dependent stacking fault energy and driving force for the formation of the LPSO phase. Eventually, the influence of the stacking fault energy on the formation of LPSO phase could be explained and the thermodynamic criteria for the formation of LPSO phase is established, which could help to control the precipitation of LPSO phase and design high performance heat resistant magnesium alloys.