合金化对单晶镍基高温合金蠕变机制和持久性能的影响

It has been proved that the elements Re/Ru may obvious improve the creep resistance of single crystal nickel based superalloys at elevated temperature. Because the reason of the elements Re/Ru enhancing the creep resistance has an important effect on the composition design of alloy, therefore, the base science problems on adding Re/Ru for enhancing solution strengthening extent of r'/r phases, hindering dislocations movement and forming K-W locking to improve the creep resistance of alloy at elevated temperature are investigated. By means of measuring the migration rate of the elements diffusion, composition analysis of elements at micro-area and the stacking fault energy of the Re-free, containing Re and Re + Ru superalloys at different temperatures, the effecting mechanisms of the Re/Ru improving the distribution of the elements in the r'/r phases and microstructure stability of superalloys are obtained. And the reason of the elements Re/Ru decreasing the strain rate of single crystal nickel based superalloys is put forth by measuring creep properties and internal friction stress of dislocations movement during steady state creep. By means of TEM microstructure observation and contrast analysis of dislocations configuration, the temperature zone of elements Re/Ru enhancing the formed K-W locking are confirmed so that the reasons of the forming or eliminating K-W locking at different temperatures are investigated to put forward the effecting mechanism of the Re/Ru improving the creep resistance of alloys. This may perfect the theory of the Re/Ru alloying improving the creep behaviors of single crystal nickel based superalloys at elevated temperature.

元素Re/Ru可明显提高单晶镍基合金的高温蠕变性能，由于研究元素Re/Ru提高合金蠕变抗力的作用机理对成分优化设计有重要启示作用。据此，开展加入Re/Ru增进r'、r两相固溶强化程度，阻碍位错运动，提高形成稳定K-W锁的温度范围以改善高温蠕变抗力的研究工作。通过测算无Re、含Re和含（Re + Ru）合金在不同温度的层错能、元素扩散迁移率及微区成分分析，提出元素Re/Ru对r'/r两相元素分布规律的影响及提高组织稳定性的作用机理；通过测定蠕变性能、稳态蠕变期间位错运动的内摩擦应力，提出元素Re/Ru可降低单晶合金稳态蠕变期间应变速率的原因；通过高分辨TEM形貌观察、位错组态的衍衬分析，确定元素Re/Ru提高合金蠕变期间形成K-W锁的温度区间，研究合金在不同温度区间K-W锁的形成及消除原因，提出元素Re/Ru提高合金蠕变抗力的作用机理，以完善合金化改善单晶合金高温蠕变行为的理论。

针对先进航空发动机叶片部件使用的第四代单晶镍基合金的开发，设计及制备出含4.5%Re/3%Ru单晶镍基合金，研究了元素Re/Ru对合金元素分布、组织稳定性和层错能的影响，通过蠕变性能测试、组织观察及位错组态的衍衬分析，研究了元素Re/Ru对合金蠕变性能、蠕变期间变形机制及形成与消除K-W锁的影响规律。结果表明，元素Cr、Re、W、Mo富集于枝晶干，Al、Ta、Ru、Co富集于枝晶间区域；经高温固溶及完全热处理后，可明显提高合金成分的均匀化程度，及中、高温蠕变抗力。无Re/Ru单晶合金有较高的层错能及较低的高温蠕变性能，加入Re/Ru可大幅度降低合金的层错能，并明显提高合金在高温的蠕变性能，使设计的4.5%Re/3%Ru单晶镍基合金在1100 oC/137 MPa的蠕变寿命达到321h，与第四代单晶合金的国际水平相当。其中，1085oC蠕变期间仍可保留K-W锁，是合金具有良好高温蠕变抗力的原因之一。.温度对合金的层错能及变形机制有明显的影响，测算出含 Re合金在760 oC、980 oC和1070 oC的层错能分别为：128.1 kJ/mol、281.2 kJ/mol和349.1 kJ/mol，其中，含Re合金在760℃有较低层错能，蠕变期间切入γ'相的位错可发生分解，形成不全位错+SISF层错的位错组态，位错也可由｛111｝面交滑移至｛100｝面，形成K-W锁；随温度提高到980℃，层错能提高，蠕变期间剪切进入γ'相的螺位错仅形成K-W锁 +（APB）的位错组态，随蠕变温度进一步提高到1070oC，合金中K-W锁消失，合金的变形机制仅为<110>螺、刃超位错剪切γ'相。合金在中温/髙应力蠕变期间，主、次滑移系交替开动，可致使微裂纹及孔洞在垂直于应力轴的γ'/γ两相界面处萌生，沿<110>方向扩展，使其在（001）面形成正方形解理面，直至蠕变断裂，是合金在中温/高应力蠕变期间的断裂机制。高温蠕变后期，大量位错的交替滑移，使筏形γ'/γ两相扭曲，并在扭曲的筏形γ'/γ两相界面发生裂纹的萌生与扩展，直至断裂，是合金在高温蠕变期间的断裂机制。