抗热腐蚀单晶高温合金的热腐蚀及长时蠕变机理研究

Industrial gas turbines are major equipments for the national development strategy of clean energy. Hot corrosion resistant single crystal (SX) superalloys are key engineering materials of hot-section components in advanced gas turbine systems, operating in hot corrosion environment and under complex loading at high temperature for long time (>20,000h). Compared with the established strengthening mechanisms in high-strength SX superalloys used in aero engines, the systematic investigations on hot corrosion mechanism and long term creep mechanism have not been conducted yet. Several critical issues are still unclear in hot corrosion resistant SX alloys, including the influence of key elements on hot corrosion mechanism and long term creep degradation behaviors as well as the major strengthening mechanisms at different stages during service. Therefore, the progress for fundamental understanding of alloy design and development has still been limited in hot corrosion resistant SX alloys at present..Based on the service conditions of hot corrosion resistant SX alloys, the objectives of the current project focus on the influence of some key elements (Ta, Re and S) on hot corrosion behaviors and mechanism as well as high temperature creep damage mechanisms at different stages during long term service. This study is to explore new approaches for improving mechanical properties of SX superalloys, while maintaining excellent corrosion resistance and long-term microstructural stability. The project will finally develop some modeling approaches for alloy design and optimization of hot corrosion resistant SX alloys, and provide fundamental understanding for developing domestic key engineering materials with proprietary intellectual property rights in advanced industrial gas turbines.

燃气轮机是实现我国清洁能源战略的关键装备。抗热腐蚀单晶高温合金是先进燃气轮机的核心热端材料，在热腐蚀、高温、复杂载荷等苛刻环境下长期工作（>20000小时）。与目前发展较为完备的航空发动机用高强单晶合金理论体系相比，由于缺乏对热腐蚀机理和长时蠕变机理的系统研究，关键元素对热腐蚀行为的影响机理存在争议，长时蠕变不同阶段的强化机制尚不明确，导致抗热腐蚀单晶合金成分设计理论和方法的发展相对落后。本项目针对抗热腐蚀单晶合金的服役环境特点，深入研究Ta、Re、S等关键合金元素和杂质元素对单晶合金高温热腐蚀行为和机理、高温长时蠕变变形和损伤机制的影响，揭示抗热腐蚀单晶合金在复杂环境下长时服役不同阶段的主要损伤机理，探索在兼顾抗热腐蚀性能和长期稳定性的基础上，改善先进燃气轮机用单晶合金综合力学性能的新思路，提出高强抗热腐蚀单晶合金成分设计优化的新准则，为我国先进燃气轮机关键材料的自主研发奠定理论基础。

燃气轮机是实现我国清洁能源战略的关键装备。抗热腐蚀单晶高温合金是先进燃气轮机的核心热端材料，在热腐蚀、高温、复杂载荷等苛刻环境下长期工作。与目前发展较为完备的航空发动机用高强单晶合金理论体系相比，由于缺乏对热腐蚀机理和长时蠕变机理的系统研究，关键元素对热腐蚀行为的影响机理存在争议，长时蠕变不同阶段的强化机制尚不明确，导致抗热腐蚀单晶合金成分设计理论和方法的发展相对落后。因此，本项目针对抗热腐蚀单晶合金的服役环境特点，深入研究了Ta、Re、S等关键合金元素和杂质元素对单晶合金高温热腐蚀行为和机理的影响，阐明了Ta和Re元素在长时蠕变中的强化作用机理，确定了Ta和Re元素对合金组织稳定性的影响规律。首次在高温合金腐蚀产物中发现了TaS2以及TaS2与CrSx之间的转换，并基于热力学和动力学因素进行了合理解释。发现了含Re合金热腐蚀动力学遵循多段抛物线规律，ppm级S含量的变化也可明显恶化合金的氧化和热腐蚀性能。与短时位错蠕变相比，合金长时变形行为主要受控于扩散蠕变。Ta和Re元素的添加细化了合金γ′相组织，显著阻碍了合金元素扩散、延缓了位错运动，降低了合金最小蠕变速率。同时，Ta和Re元素促使合金“N”型筏排组织的形成，结合相界面和特征缺陷处的重元素偏聚，进一步提高合金长时蠕变寿命。在长时热暴露过程中，Ta和Re元素的加入都降低了合金γ′相的粗化速率和γ/γ′两相错配度，促进了合金TCP相的析出。优化了高强抗热腐蚀单晶合金设计准则，设计并研制出了第二代抗热腐蚀单晶合金的原型合金。通过本项目的研究，不仅可以进一步加深我们对复杂合金体系热腐蚀和长时蠕变行为的理解，而且将为发展我国燃气轮机用关键单晶合金奠定扎实的理论基础。