多组元交互作用对第四代单晶高温合金组织稳定性和蠕变行为的影响规律

To meet domestic demands of advanced aircraft engines with high thrust-weight ratio, it is necessary to develop the fourth generation Ni-based single crystal superalloys containing Re and Ru, independently. But the expensive cost of Re and Ru restricts their application in aerospace industry. Meanwhile, the mechanisms based on the influence of Co and Ru on microstructural stability and the interaction effect of Mo and Cr on creep behavior are still controversy, due to the complex effects of multiple alloying elements in single crystal superalloys. Clarifying the mechanisms associated with these alloying elements is beneficial to understand whether they can substitute for Re and Ru..In the current study, eight experimental alloys containing low content of Re were designed with various levels of Co, Ru, Mo and Cr additions based on our previous studies. According to general principles of physical metallurgy, the quantitative analyses of elemental partitioning ratios and lattice misfits will be carried out by using advance techniques of materials characterization. The relationship among alloying elements, elemental partitioning ratios, lattice misfits, microstructural stability associated with the precipitation of TCP phases and the rafting behavior of γ' phase, dislocation configurations under creep deformation and creep behavior will be investigated in details. This work will clarify both individual and interactive effects of Ru, Co, Mo and Cr on microstructural stability and creep behavior at high temperature and the priority of these alloying effects will be also determined. The implementation of this project will provide a scientific basis for alloy design and optimization of new generation single crystal superalloys with low-cost, low-density and high-performance.

自主研发含Re和Ru的第四代单晶高温合金已成为我国高推重比航空发动机的战略需求；而Re和Ru价格昂贵，是制约其应用的主要因素之一。目前，国际学术界在复杂多组元的单晶高温合金中针对Co与Ru对组织稳定性的影响机理和Mo与Cr交互作用对蠕变性能的影响规律尚不明确。对上述科学问题的解决有助于认识它们对Re和Ru的替代作用。.在已结题的基金项目（50671015）和前期研究工作基础上，本项目设计八种低Re的实验合金，从合金元素分配比和错配度的定量分析入手，系统研究合金元素、成分分配比、错配度、组织稳定性（TCP相析出和γ'相筏排化）、加载下的位错组态及组织演变与蠕变性能之间的关系，阐明Ru、Co、Mo和Cr等四种元素的独立和交互作用对镍基单晶高温合金组织稳定性和蠕变性能的影响规律，并确定主次影响因素。本项目的实施将为低成本、低密度、高性能的新一代单晶高温合金成分设计与性能优化提供科学的依据。

镍基单晶高温合金具有优异的高温综合性能，是先进航空发动机高压涡轮叶片的首选材料。自本世纪以来，以含Re和Ru为特征的第四代单晶合金成为国际高温合金领域的主要研究重点之一。由于合金化程度极高，多组元交互作用对单晶合金组织与性能的影响机理复杂。发挥各合金元素的有益作用，探索部分替代贵重金属Re和Ru的途径，以降低合金密度与成本是当代镍基单晶高温合金成分设计与优化中最具有挑战性的研究问题。. 在课题组的前期研究工作基础上，本项目通过分式析因设计方法设计十种低Re的实验合金，系统研究了Co（~7.0/~15.0wt.%）、Cr（~3.5/~6.0wt.%）、Mo（~1.0/~2.5wt.%）和Ru（~2.5/~4.0wt.%）等元素对γ和γ′两相的成分分配行为、γ/γ′错配度、TCP相的析出以及1100℃/140MPa和950℃/400MPa条件下的蠕变性能、组织演变和位错组态的影响规律，分析了四种元素独立和交互作用对合金高温组织稳定性和高温蠕变行为的影响机理。研究表明：Co和Ru元素降低了Re、W、Mo和Cr元素的γ/γ′两相成分分配比，而Cr和Mo则起相反作用。Co、Cr、Mo和Ru四种元素的添加分别提高了γ/γ′错配度大小。950℃和1100℃条件下的高温长时热暴露实验结果表明：Cr和Mo分别显著促进了低Co合金中σ相和P相的析出；而高Co合金中析出的TCP相为富Co的μ相和R相，它们分别在950℃和1100℃稳定存在。1100℃/140MPa条件下的蠕变性能主要受γ/γ′相界面位错网络结构和TCP相的影响。Ru的添加提高了γ/γ′相错配度和界面位错网络间距，对蠕变性能有利；Cr和Mo的添加促进蠕变过程中TCP相的析出从而降低合金的蠕变寿命。950℃/400MPa蠕变条件下的蠕变性能主要受γ′相体积分数，错配度和TCP相的影响；而高Co合金γ相中层错的出现也是提高合金蠕变性能的主要原因之一。. 通过本项目的研究，为以Co替代部分Ru元素，从而降低单晶合金的成本提供了科学的依据。同时，综合考虑Mo和Cr对蠕变强化的有利作用和对有害TCP相的促进作用，为组织稳定性和蠕变性能高的新一代单晶合金成分设计和优化提供了实验指导和理论依据。