| 钌在镍基单晶高温合金中的作用 | |
| Alternative Title | Role of Ruthenium in Ni-based Single Crystal Superalloys |
| 金涛 | |
| Subtype | 博士 |
| Thesis Advisor | 胡壮麒 |
| 2009-05-31 | |
| Degree Grantor | 中国科学院金属研究所 |
| Place of Conferral | 金属研究所 |
| Degree Discipline | 材料学 |
| Keyword | 单晶高温合金 钌 凝固 组织稳定性 性能 |
| Abstract | 本文采用扫描电镜（SEM）、透射电镜（TEM）、示差扫描量热分析（DSC）和能谱分析（EDS）等方法研究了不同Ru含量（0、1.5、3wt.％）对镍基单晶高温合金的凝固行为、热处理与长期时效后的组织变化、拉伸和持久性能以及高温氧化腐蚀行为的影响。研究结果表明： 在以6mm/min的抽拉速率定向凝固后，三种合金的铸态组织均为枝晶组织，含3wt.％Ru的合金中还出现了NiAl相。随着Ru含量的增加，枝晶间距、铸态和固溶及时效处理后的γˊ相尺寸均减小，γ/γˊ共晶含量降低，合金的初熔温度和γˊ相析出温度也降低，但固、液相线温度变化不大。 Ru元素偏聚于枝晶干。Ru的加入明显影响其它合金元素的偏析，加入1.5wt.％的Ru后，Al和Ta等枝晶间富集元素更多地向枝晶干分配，W和Re等枝晶干富集元素向枝晶干偏聚的趋势更强；而加入3wt.％的Ru后，Al和Ta等元素更多地向枝晶间偏聚，Re元素向枝晶干偏析的倾向减弱。 加入Ru导致明显的元素反分配现象，即γˊ相形成元素更多地分配于γ基体，而γ基体形成元素更多地分配于γˊ相。在1100℃长期时效过程中，µ相的析出时间随Ru含量的增加而推迟，Ru具有明显的抑制TCP相的作用。但Ru的加入增大了γˊ相的长大速率。 三种合金的抗拉强度在760℃时均达到峰值，Ru表现出明显的强化作用。800℃时的抗拉强度有所下降，其中3wt.％Ru合金的下降幅度最显著。1000℃时的抗拉强度急剧降低，且随Ru含量的升高性能降低的趋势略有加强。在1100℃/180MPa试验条件下，不含Ru和含3wt.％Ru合金的蠕变寿命非常接近，而1.5wt.％Ru合金的寿命明显降低。在1000℃/310MPa条件下，不含Ru和含1.5wt.％Ru合金的蠕变寿命非常接近，3wt.％Ru合金的寿命明显低于前两种合金，延伸率却显著提高。拉伸蠕变时合金中析出的m相可以作为基底促进孔洞形核，进而促进微裂纹快速连接甚至直接诱发裂纹。加入1.5wt.％Ru可推迟m相形核从而减小孔洞尺寸；加入3wt.％Ru几乎完全抑制了μ相的析出。但Ru同时降低筏形组织的稳定性。Ru对性能的影响取决于这两方面作用的竞争结果。 三种合金的氧化动力学曲线均符合抛物线规律。Ru的加入使氧化表观激活能增加。含Ru合金在1000℃和1100℃氧化时具有更高的氧化速率，在900℃氧化初期，枝晶间和枝晶干表现出不同的氧化行为。 1100℃氧化后，三种合金的氧化膜从表面向内依次为：NiO外层、CrTaO4、(Ni,Co)(Cr,Al)2O4、(Ni,Co)Ta2O6和NiWO4尖晶石次外层和α-Al2O3内层。900℃和1000℃氧化后的氧化层与1100℃基本相同，仅在次外层中不含NiWO4氧化物。三种合金均发生不同程度的内氮化。Ru在一定程度上降低了镍基单晶高温合金的抗高温热腐蚀性能（950℃，Na2SO4）。初期腐蚀产物均主要由外层NiO、内层(Ni,Co)Al2O4和NiTa2O6组成。 |
| Other Abstract | In this dissertation, single crystal superalloys with different contents of Ru addition (0, 1.5, 3.0wt.%) were employed to study the influence of Ru addition on the as-solidified microstructure, structural evolution during heat treatment and long term aging, tensile and stress rupture properties, and oxidation behavior by using scanning electron microscope (SEM), transmission electron microscope (TEM), differential scanning calorimetry (DSC), energy dispersive spectroscopy (EDS) and some other research methods. All the three kinds of alloys with different Ru content were directionally solidified with a 6mm/min withdrawal rate and the microstructures of the alloys were dendritic structures. β-NiAl phase particles with blocky morphology formed in the alloy with 3wt.% Ru content. With the increment of Ru content, the dendrite arm spacing and the volume fraction of γ/γˊ eutectics decreased. The size of γˊ phase after solidified and solution and aging treatment also decreased. The liquidus and solidus of the alloys did not change a lot. But the incipient melting temperature and γˊsolvus temperature of the alloys dropped. The investigation of segregation behavior for alloying elements showed that Ru was apt to segregation to dendritic core region. The segregation of other alloying element was apparently influenced by addition of Ru. With 1.5wt.% Ru addition, the accumulation of elements Al, Ta, etc. towards interdendritic area became smaller and refractory elements like W, Re towards dendrite core were enhanced. When Ru addition further increased to 3wt.%, the segregation trends of Al, Ta turned reversely. But the segregation trends of Re became more significant with the rise of Ru content in the alloy. With more Ru content in the alloy, an apparent inverse distribution of alloying elements was observed, which was more γˊ forming elements distributing to the matrix and more matrix forming elements distributing to the γˊ phase. During long term aging, µ phases precipitated in the Ru-containing alloys much later than Ru-free alloy. Ru can effectively suppress the precipitation of TCP phases. But Ru addition accelerated the coarsening of γˊ phase. The tensile test showed that Ru has revealed pronounced strengthening effect on the tensile properties. All the three alloys with different Ru content reached their peak tensile strength at 760℃. When the tensile tested temperature increased to 800℃, the tensile strengths of three alloys decreased a little, the alloy with 3wt.% Ru content showed the most obvious decreasing amplitude. At 1000℃, the tensile strengths of three alloys decreased dramatically, and the alloy with less Ru addition showed slightly higher strength than that with more Ru content. In the stress rupture tests, the Ru free alloy possessed almost the same stress rupture life with the alloy of 3wt.% Ru content at 1100℃/180MPa, while the alloy of 1.5wt.% Ru content had a much lower rupture life. However, at 1000℃/310MPa, the Ru free alloy and 1.5wt.% Ru containing alloy possessed similar rupture lives, while the alloy with 3wt.% Ru had an apparently lower stress rupture life and a higher elongation. When m phase precipitates in the alloy during stress rupture tests, they can act as substrate to promote the nucleation of pores, and further accelerate the connection of micro-cracks or even induce the formation of cracks. With 1.5wt.% Ru addition, the nucleation of m phase can be retarded, so the pore sizes were reduced. With 3wt.% Ru addition, the precipitation of m phase can be completely eliminated, which was beneficial to obtaining higher stress rupture life. However, Ru destabilized the raft like microstructure, which was deleterious for the mechanical properties of single crystal superalloys. It was considered that the influence of Ru on the mechanical properties of single crystal superalloys depended on the competition of the above beneficial effect and deleterious effect. Same as Ru free single crystal superalloys, Ru containing alloys had the same oxidation kinetic curves which obeyed the parabolic rule. Comparing with Ru free alloy, the Ru containing alloys had higher oxidation rates at 1000℃ and 1100℃. At 900℃, the dendrite core region and interdendrite region revealed different oxidation behavior during the early stage of oxidation in Ru containing alloys. Ru addition increased the apparent activation energy of oxidation. After oxidation at 1100℃, the Ru free alloy and Ru containing alloys had the same phases distribution in the oxide films along the specimen surface towards the interior of the alloys, which were NiO (outer layer), CrTaO4, (Ni,Co)(Cr,Al)2O4, (Ni,Co)Ta2O6, and NiWO4 spinel phase (intermediate), a-Al2O3 (inner layer). The oxide films formed at 900℃ and 1000℃ were almost same as that at 1100℃, but they did not contain NiWO4 oxide in the intermediate. Besides, all the alloys had some extent of inner nitride under the three selected oxidation temperatures. The hot corrosion resistance of the single crystal superalloys has been decreased for some extent by the addition of Ru. The corrosion products at early stage were composed by NiO in the outer layer and (Ni,Co)Al2O4, NiTa2O6 in the inner layer. |
| Pages | 144 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.imr.ac.cn/handle/321006/16939 |
| Collection | 中国科学院金属研究所 |
| Recommended Citation GB/T 7714 | 金涛. 钌在镍基单晶高温合金中的作用[D]. 金属研究所. 中国科学院金属研究所,2009. |
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