【作者】 于潇翔；

【导师】 王崇愚；

【作者基本信息】 清华大学 ， 材料科学与工程， 2012， 博士

【摘要】 化学成分对于镍基单晶高温合金力学性能具有重要影响，多组元固溶元素的作用和它们之间的相互影响以及协同效应具有重要的科学内涵和研究意义。本文对镍基单晶高温合金中化学元素——结构缺陷复合体电子结构与材料物性相关机制及Re和Ru元素协同效应进行了理论和实验研究。本文基于第一原理电子结构计算和位错线弹性理论发展了多尺度序列模式——物理参量解析传递算法，并将该算法用于镍基单晶高温合金力学性质研究。通过第一原理计算了合金元素对γ-Ni中层错能以及空位扩散激活能的影响，通过物理参量解析传递，计算了合金元素对Ni中位错攀移速度的影响。结果表明Re，Mo和W元素能够通过提高割阶形成能和空位扩散势垒有效地抑制位错攀移，从而提高了合金的蠕变强度和寿命。我们研究了合金元素对γ-Ni3Al中面缺陷能量及广义堆垛能的影响。通过物理参量解析传递，评估了合金元素对γ相中位错交滑移激活焓的影响，进而可以定性地了解合金元素强化γ相的能力。结果显示Re元素能够比W、Ta、Ti和Ru元素更有效地提高Ni3Al的流变应力。另一方面，根据Rice的韧脆判据，Re元素会使γ相变得更脆，有利于裂纹解理断裂。本文设计了Ni-Al二元，Ni-Al-Re和Ni-Al-Ru三元以及Ni-Al-Re-Ru四元模型合金，结合透射电子显微镜和三维原子探针实验，实现对合金相内区及界面区多化学元素分布特征及原子尺度构型的观测。实验结果表明，Ru的加入使得Re原子从γ相向γ相转移，并在γ相内形成Re-Ru原子团。第一原理计算结果显示，Re和Ru原子在第四近邻(大约5)范围内存在相互吸引作用，且距离越近，吸引作用越强。键强分析显示Re-Ru成键强度比Re-Ni和Ru-Ni键大，Re和Ru之间的强键合源于Re和Ru原子之间存在d-d电子杂化。更多还原

【Abstract】 Chemical compositions are critical to the mechanical properties of Ni-basedsingle-crystal superalloys. The strengthening mechanisms of multi-chemical alloy-ing elements, their interactions and synergistic efects are of great significance in bothscience and engineering application. By using sequential multiscale modeling, the re-lationship between the electronic structure of alloying element-fault complex and me-chanical properties of superalloys are studied. Besides, the synergistic efect of Re andRu in Ni-based single-crystal superalloys are explored via theoretical and experimentalmethod.The efects of alloying elements on stacking fault energy and difusion activationenergy of vacancy in Ni are calculated by first-principles. The results are used asthe input parameters for analytical expressions based on elastic dislocation theory toevaluate the efects of alloying elements on the velocity of dislocation climbing in γ-Niphase. The results suggest that the elements Re, Mo and W can efectively suppressthe velocity of dislocation climbing by raising both the jog formation energy and thedifusion barrier of the vacancy.First-principles electronic structure calculations are used to study the influences ofalloying elements on the planar fault energies and generalized stacking fault energies inNi3Al. In combination with dislocation theory, the evaluation of strengthening efectsof various alloying elements can be given. Re is found to be more efective than W,Ta, Ti and Ru in decreasing cross-slip activation enthalpy and increasing flow stressin γ-Ni3Al. Meanwhile, according to Rice-criterion, Re increases brittleness of Ni3Almost, which promotes the probability of cleavage fracture near crack tip.Four kinds of single-crystal model alloys are designed, including Ni-Al, Ni-Al-Re,Ni-Al-Ru and Ni-Al-Re-Ru alloys. Three-dimensional atom probe tomography andhigh-resolution scanning transmission electron microscope are used to attain atomicscale resolution and obtain direct experimental evidence of element partitioning and site preference. The results show that the addition of the element Ru drives Re torepartition to γ phase and form Re-Ru clusters. First-principles calculations indicatethat Ru and Re attract each other in the range of4thnearest neighbor (about5),the attraction becomes stronger as the distance between Re and Ru decreasing. Theanalyses of bonding strength shows that Re-Ru bonding is stronger than Re-Ni and Ru-Ni, the strong interaction between Re and Ru originates from d-d orbital hybridizations.更多还原