预氧化高熵合金在熔铝中的界面反应控制及相关相平衡的研究

The corrosion failure of materials in molten aluminum is a critical factor constraining the development of aluminum industry. The preferential corrosion of solid solution and the cracking of oxide film are the two major reasons for the failure. Unfortunately, the existing approaches and technologies have failed to simultaneously deal with these two difficult problems. Given that high-entropy alloy (HEA) and high-entropy oxide (HEO) have the sluggish diffusion effect and the good thermal stability property respectively, if a pre-oxidation HEA can be designed and prepared, it will hopefully improve the corrosion resistance of solid solution and the stability of oxide film simultaneously. In the project, the determination of phase diagrams, the design of HEA, the optimization of oxidation process and the interfacial reaction in the molten aluminum will be investigated systematically in the Al-Co-Cr-Fe-Ni-Si-Ti-Zr alloy system via CALPHAD, diffusion couple, Dictra method, micro-arc oxidation and hot-dipping. SEM/EDS, XRD and TEM will be synthetically applied into the above studies. The chemical composition and temperature ranges for high-entropy solid solution will be confirmed. The formation and growth of the HEA oxide layer will be clearly illuminated, and the control mechanism of the interfacial reaction of pre-oxidation HEA in molten aluminum will be discussed and established in the project. The results of the project will not only deepen the understanding of the theory of alloys design and the mechanism of liquid metal corrosion, but also provide the theoretical and technical basis for the material selection in molten metal environment.

材料的耐熔铝腐蚀问题是制约铝工业发展的关键因素。固溶体的择优腐蚀和氧化膜的破裂是材料在熔融金属中腐蚀失效的主要原因，现有的方法难以同时解决这两大难题。基于迟滞扩散的高熵固溶体和热稳定的高熵氧化物，设计出预氧化高熵合金，有望同时提高固溶体的耐蚀性和氧化膜的稳定性。本项目以Al-Co-Cr-Fe-Ni-Si-Ti-Zr体系为研究对象，通过相图和扩散系数的实验测定，利用CALPHAD和Dictra对合金体系进行热力学和动力学过程的计算与模拟，结合微弧氧化和浸镀实验，系统地开展相图测定、高熵合金设计、氧化工艺优化和熔铝界面反应控制等方面的研究，确定高熵固溶体的成分和温度范围；阐明高熵合金氧化过程中氧化层形成及生长规律；揭示熔铝中预氧化高熵合金的界面反应控制机理。本项目的研究成果既能深化对合金设计理论和液态金属腐蚀机制的认识，也能为熔融金属环境中材料的选择提供理论和技术支持。

为解决制约铝工业发展的耐熔铝腐蚀问题，本项目基于迟滞扩散的高熵固溶体和热稳定的高熵氧化物，设计出预氧化高熵合金，同时提高固溶体的耐蚀性和氧化膜的稳定性，从而制备出耐熔铝性能优越的合金。本项目实行期间完成了以下研究内容：1、实验测定了体系的部分相关系，获得第三组元在Fe2B和Fe2Mo中的溶解度；2、较为系统地研究了预氧化前后AlxCoCrFeNi 高熵合金耐熔铝腐蚀性能及界面反应机理，分析高熵合金迟滞扩散效应在局部熔铝界面反应过程中的作用；3、较为系统地研究了FeB-AlFeNiCoCr、FeB-Mo-AlFeNiCoCr、FeB-Mo-Al0.25FeNiCoCr、Ti(C,N)-Al0.25FeNiCoCr、TiB2-(Fe-Co-Cr-Ni)、ZrB2-AlFeNiCoCr多种金属陶瓷制备及其耐熔铝腐蚀性能的研究；以上研究对于促进铝工业的发展具有重要的理论意义和应用价值。