以Mo代W对镍基单晶高温合金γ/γ'元素分配行为与高温持久性能的影响机制

The development of low density single crystal superalloy with excellent high temperature stress rupture properties is of great is of great significance to improve the thrust-weight ratio of aeroengine. Substituting Mo for W can effectively decrease the density of Ni-based single crystal superalloy. However, its effect on high temperature stress rupture properties is still unclear and deserves to be further investigated. In this project, some second generation single crystal superalloys with different Mo and W contents will be selected as the research project. By using first principle method, quasi harmonic approximation and experimental approach, the influences of Mo and W on γ/γ′ partitioning behavior of alloying elements at different temperatures will be probed, and its physical essence will be clarified from the atomic level. Based on the obtained γ/γ′ partitioning behavior of alloying elements, the influence rules of substituting Mo for W and temperature on strengthening factors of stress rupture properties, such as solid solution hardening of γ phase, solid solution hardening of γ′ phase, γ/γ' lattice misfit, spacing of γ/γ' interface dislocation network and volume fraction of γ′ phase, will be analyzed. The relationship among alloy composition, strengthening factors of stress rupture properties and high temperature stress rupture properties will be established, and the main factor of high temperature stress rupture properties will be ascertained. The successful development of this project is expected to reveal the mechanism of substituting Mo for W on high temperature stress rupture properties of single crystal superalloy, and provide the theoretical foundation for the development of new type single crystal superalloy with lower density and higher temperature capability.

发展高温持久性能优异的低密度单晶高温合金对提高航空发动机推重比具有重要的意义。以Mo代W可有效降低镍基单晶高温合金的密度，然而以Mo代W对高温持久性能的影响规律与作用机制有待深入研究。本项目拟以不同Mo和W含量的二代单晶高温合金为研究对象，基于第一性原理、准谐近似方法与实验研究，从原子层面阐明Mo和W对高温下γ/γ'元素分配行为的影响规律及其物理本质。在此基础上，探究以Mo代W对γ相固溶强化程度、γ'相固溶强化程度、γ/γ'错配度、γ/γ'界面位错网间距与γ'相体积分数等持久强化因素的影响规律，构建合金成分-持久强化因素-高温持久性能之间的联系，明确高温持久性能的主控因素。本项目的顺利开展，有望揭示以Mo代W对高温持久性能的影响机制，为发展新型低密度和高承温能力的单晶高温合金提供理论依据。

为提高单晶高温合金的承温能力，先进单晶高温合金中加入了大量高密度的难熔元素（如Re和W），显著地增大了合金的密度。但是过高的密度将导致单晶涡轮叶片旋转时离心力较大，进而不利于先进单晶高温合金在高推重比航空发动机中的应用，因此高密度已成为先进单晶高温合金的发展瓶颈之一。为解决这一问题，基于以Mo代W的成分设计思想，本项目设计了高Mo强化二代单晶高温合金，与典型的高W强化单晶高温合金相比，该合金具有低密度（ρ=8.5g/cm3）、低偏析（铸态组织中Re元素的显微偏析倾向较小）、组织稳定性良好（850℃、980℃和1100℃长期时效500h后无TCP相析出）与高温蠕变性能优异（1100℃/137MPa的蠕变寿命≥170h）的特征。高Mo强化单晶高温合金高温蠕变性能优异的原因为该合金具有更负的γ/γ′错配度：一方面，Mo比W更倾向与分布在γ相中，进而增大了γ相的晶格常数；另一方面，Re元素的γ/γ′分配行为受到合金元素交互作用的影响，即Mo的添加将增大Re元素在γ相中的偏聚倾向。综上所述，以Mo代W可有效地降低γ/γ′错配度，进而提高了γ/γ′界面强度与高温蠕变性能。本项目的研究结果，可为发展新型低密度和高承温能力的新型单晶高温合金提供理论基础。