压力和温度耦合作用下高熵合金的相结构演化及相形成规律研究

The excellent properties of high entropy alloys (HEAs) are mainly determined by the microstructures formed during the solidification process, which is closely related to the composition and solidification conditions such as temperature and pressure, and directly related to the development and application of HEAs. At present, the rules of phase formation and transformation during the solidification process of HEAs have been studied by some researchers, but the research mainly considers the influence of composition and temperature, and rarely considers the pressure. AlxCoCrCuFeNi HEAs were employed as research object in this project. The phase structure transformation and solidification behavior of HEAs melt under the pressure- temperature coupling effect were studied by using high temperature and pressure technology, and the relationship between the pressure and temperature and the phase structure evolution of HEAs was expected to be established. The thermodynamic metastable phases in the solidification process of HEAs are intercepted by the influence of pressure on the atomic transfer, redistribution nucleation and growth during the liquids-solid transformation. Based on the evolution of the local atomic structure of the metastable phase, the relationship between the atomic interaction of components and the phase structure transformation in the solidification process of the HEAs is established, and the phase formation rule and its mechanism in the liquid-solid transformation process of the HEAs are clarified, which provides theoretical basis and technical support for the composition design and performance optimization of HEAs, and are of great significance for enrichment and development of solidification theory of HEAs.

高熵合金的优异性能主要由其凝固过程形成的微观组态决定，与合金的成分及温度和压力等凝固条件密切相关，直接关系到高熵合金的开发和应用。目前已有研究者开展了高熵合金凝固过程中相形成及相转变规律方面的研究，但研究工作主要考虑成分和温度的影响，很少考虑压力的影响。本项目拟以AlxCoCrCuFeNi高熵合金为研究对象，利用高温高压技术，进行压力温度耦合作用下高熵合金相结构转变及合金熔体凝固行为的研究，期望建立压力、温度与高熵合金相结构演化之间的关系，借助压力对合金熔体液固转变过程中原子传递与再分配、形核及长大的影响，截获高熵合金凝固过程中的热力学亚稳相，从亚稳相局域原子结构演化特征出发，揭示高熵合金液固转变过程中的相形成规律，阐明组元原子间相互作用与高熵合金凝固过程中相结构转变的关系，为高熵合金的成分设计和性能优化提供理论基础和技术支持，对丰富和发展高熵合金凝固理论具有重要的意义。

高熵合金具有优异的性能和广阔的应用前景，高熵合金的优异性能主要由其凝固过程形成的微观组态决定，与合金的成分和凝固条件密切相关，直接关系到高熵合金的开发和应用。但在高熵合金相形成机理及性能影响因素等方面至今仍缺乏完整的理论体系，从而大大限制了高熵合金的发展。本项目采用原位中子衍射、同步辐射X射线衍射以及机械热处理等技术研究了AlxCoCrFeNi高熵合金凝固过程中的相形成规律和极端条件下的结构演化过程。主要研究结果如下：1）利用无容器处理方法，截获CoCrFeNi高熵合金熔体凝固过程中不同温度下的热力学亚稳相，通过原位中子衍射技术，获得亚稳相结构信息，分析合金熔体凝固过程中的原子结构演化过程，建立了熔体结构与凝固相结构之间的关联，丰富了高熵合金凝固理论。2）利用高压同步辐射X射线衍射技术，研究了AlxCoCrFeNi高熵合金高压下的结构演化过程，分析了Al含量对其结构演化的影响，提供了一种通过调整成分和极端条件来调控合金结构和性能的方法。3）此外，我们通过Ti/Mo共掺杂和机械热处理技术诱导双析出相，实现了室温下CoCrNi中熵合金强度和延性平衡，并制备了一种高强度高延展性的CoCrNiTi0.1Mo0.1合金，为新型高熵合金的设计和开发提供了新的思路。通过该项目的研究，加深了对高熵合金凝固过程相形成规律和极端条件相结构演化的认识，为新型合金的设计和开发提供了重要的理论指导。