具有正错配度的新型γ′相强化钴基单晶高温合金的高温蠕变机理

The development of novel γ′-strengthened Co-base superalloys with high temperature strength and excellent hot corrosion resistance was considered as one of the seven major trends in high temperature materials technologies at Eurosuperalloys 2014 Conference，which was held every four years. However, alloy development for this class of superalloys is still in its early stage, and the lack of fundamental understanding of creep mechanisms including creep behaviors consequently restricted the engineering applications of this class of superalloys..A novel Co-base single crystal superalloy with positive γ/γ′ lattice misfit and unique creep behaviors was developed in our group. In this project, the investigations of this single crystal superalloy will be carried out on creep behaviors under high and low stress at 900 °C and 1000 °C. The evolution mechanisms of γ/γ′ microstructure and sub-microstructure, including dislocations, stacking faults and antiphase boundaries, at different creep stages will be systematically studied as well as the effects of temperature and stress on these evolution characteristics. Meanwhile, the relationship among misfit, microstructure, sub-microstructure and creep behaviors will be built up. High temperature creep mechanisms of novel Co-base single crystal superalloys with positive γ/γ′ lattice misfit will be revealed by means of the comparison with those of Ni-base single crystal superalloys with negative γ/γ′ lattice misfit. This study will provide the basis of physical metallurgy for alloy design and development of novel Co-base superalloys, and it will also be helpful for fundamental understanding of strengthening and toughening mechanisms in γ/γ′ two-phase superalloys.

高强、耐热腐蚀的新型γ′相强化钴基高温合金被每四年一届的欧洲高温合金大会（2014年）列为高温材料技术未来发展的七大趋势之一。但是，目前该类合金的研发仍处于初级阶段，且对其蠕变行为和机理知之甚少，严重阻碍了其工程应用。.本项目在前期工作基础上，以自主研发的钴基单晶高温合金为研究对象，针对其具有正错配度、特殊的蠕变行为特征以及900℃以上蠕变研究匮乏的现状，系统研究其在900℃和1000℃（高、低应力）的蠕变行为、蠕变不同阶段γ/γ′两相微观组织演变规律以及位错、层错和反相畴界等晶体缺陷的形成与演变机制，建立“错配度-微观组织-亚微观组织-蠕变行为”之间的关系；进而研究温度和应力对上述问题的影响机理。通过与负错配度的镍基单晶高温合金对比分析，揭示具有正错配度的钴基单晶高温合金高温蠕变机理，为新型钴基高温合金的强度设计理论提供物理冶金依据，也为丰富和发展γ/γ′两相合金的强韧化理论奠定基础。

航空发动机和燃气轮机是航空、舰船和能源等领域的核心装备，其研发和制造水平直接关系到国防安全、经济发展和国家竞争力。作为新一代清洁能源动力装置的地面燃气轮机和海航用航空发动机，其关键热端部件-涡轮叶片面临着高硫、高盐、高温、高载荷等恶劣的服役环境。因此，必须开发具有高强、耐热腐蚀的新型高温结构材料，而γ′相强化钴基高温合金被国际上认为是具有竞争力和应用潜力的材料。目前该类合金的研发仍处于初级阶段，对其蠕变行为和机理知之甚少，严重阻碍了其工程应用。.在课题组前期研究基础上，以自主研发的具有正错配度的Co-Al-W-Ta-Ti五元钴基单晶高温合金为研究对象，系统研究了实验合金在不同温度和应力条件下的蠕变行为、蠕变不同阶段γ/γ′相微观组织以及位错、层错等亚微观组织的演变规律及其交互作用对蠕变行为的影响机制，揭示了不同温度和应力条件下的蠕变机理。研究表明：对比负错配度的镍基单晶高温合金，正错配度的钴基单晶高温合金在不同温度和应力条件下的蠕变行为存在明显的特殊性：稳态蠕变速率大于最小蠕变速率。高温蠕变机理方面，蠕变初期，两种合金的变形机理无明显差异，均由位错和筏排组织控制；蠕变中后期，钴基单晶高温合金γ′相中层错及其交互作用的形成会提高合金的蠕变抗力，起主要的强化作用；合金元素在层错及其交互作用结构处的偏析行为会对蠕变抗力产生影响；温度和应力的变化会改变钴基单晶高温合金γ′相中的主要形变亚结构，进而影响蠕变机理。.通过本项目的研究，明确了一定温度和应力范围内γ′相强化钴基单晶高温合金的蠕变行为和机理以及层错等缺陷处合金元素偏析对蠕变抗力的影响，对未来新一代γ′相强化钴基单晶合金承温能力的提高和成分优化提供了实验指导和理论依据。