多元多尺度增强K4169镍基高温合金的蠕变强化机理研究

The service temperature enhancement of large casting with complex structure in aeroengine is demanded to meet the requirement of the performance improvement of advanced aeroengine. It is urgent to develop the equiaxed grain cast nickel base superalloy with excellent high temperature properties above 700℃ while keeping preferred processing properties. A novel muiti-scale multiphase reinforced nickel base superalloy with satisfied castability was prepared through increasing the MC carbide ratio in K4169 by the applicants. The high temperature properties of this MC/K4169 superalloy are greatly improved by the strengthening effect of micron-scale MC and nano-scale γ′ phase. The stress transfer effect from MC carbide is the key factor to enhance the high temperature performance of the MC/K4169 superalloy. However, the synergistic strengthening mechanism of MC carbide and γ′ phase in MC/K4169 superalloy under long term high temperature creep is not clear yet, which severely restricts the research and application of muiti-scale multiphase reinforced nickel base superalloy. In this project, synchrotron radiation X-ray diffraction is used to quantitatively study the stress distribution behavior during the creep of MC/K4169 superalloy. Combined with the stress distribution behavior, the microstructure evolution and the dislocation patterns near the creep fracture, the creep strengthening mechanism can be well revealed. This research work has important guiding significance for the design optimization of muiti-scale multiphase reinforced nickel base superalloy, which can provide theoretical guidance for the development of new type equiaxed grain cast nickel base superalloy with excellent high temperature properties and preferred processing characteristics.

先进航空发动机性能提升对其使用的大型复杂结构铸件的服役温度提出了更高要求，亟需研制700℃以上高温性能优异且工艺性能优良的等轴晶铸造镍基高温合金。项目小组基于K4169合金，通过提高其MC碳化物比例，开发了多元多尺度增强K4169合金，利用微米尺度MC碳化物和基体中γ′相的强化作用显著提升K4169合金高温性能同时保持了良好工艺性能。MC的应力承载作用是多元多尺度增强K4169合金高温性能优异的关键因素，但高温长时蠕变条件下MC和γ′相协同强化机制尚不清楚，严重制约了多元多尺度增强高温合金材料的研究与应用。本项目拟采用同步辐射X射线衍射定量研究多元多尺度K4169合金蠕变过程中多相应力分配演变行为，结合显微组织演化及长时蠕变断口附近位错组态，揭示其蠕变强化机理。相关研究工作对多元多尺度增强镍基高温合金的优化设计具有重要指导意义，可为兼具高温性能和工艺性能的新型镍基高温合金开发提供理论指导。

先进航空发动机性能提升对其使用的大型复杂结构铸件的服役温度提出了更高要求，亟需研制700℃以上高温性能优异且工艺性能优良的等轴晶铸造镍基高温合金。本项目以所研制的700℃高温性能优异且工艺性能优良的MC/K4169合金为研究对象，以揭示其高温长时蠕变条件下MC和γ′相协同强化机制为目标，系统研究了MC/K4169合金的显微组织；分析了不同服役条件下材料的组织演变规律；研究了MC/K4169合金的高温蠕变行为；结合同步辐射技术和原位拉伸实验，量化研究了MC/K4169合金中基体和MC碳化物颗粒的应力分配行为；揭示了MC/K4169合金的蠕变强化机理。.MC/K4169合金的MC碳化物颗粒在基体中均匀分布；抑制了亚稳相γ″相的形成，以热稳定性更好的γ′相作为主要沉淀强化相，获得了合理的纳米沉淀析出强化相比例；未形成有害的δ相，且脆性相Laves相的数量大幅减少。MC/K4169合金的相组织和晶界在704℃下热暴露3000h前组织基本不发生变化。在704℃高温下，当外应力是300 MPa、450 MPa和620 MPa时，MC颗粒承载的平均应力分别为1022 MPa、1226 MPa和1839 MPa，基体受力分别为262 MPa、409 MPa和556 MPa，颗粒的承载效果使基体所受应力下降10%左右。镍基复合材料蠕变在704℃和650℃时蠕变速率大幅提升的原因是门槛应力、MC颗粒的承载效应和热错配效应。MC/K4169合金的高应力下稳态蠕变由位错攀移运动控制，而低应力下主要受扩散和晶界滑动控制。与K4169合金相比，MC/K4169合金的704℃/620 MPa材料蠕变寿命大幅提升，蠕变断裂方式为穿晶断裂。.相关研究工作对多元多尺度增强镍基高温合金的优化设计具有重要指导意义，可为兼具高温性能和工艺性能的新型镍基高温合金开发提供理论指导。