| 几种镍基高温合金η相和σ相变及Re对凝固行为影响研究 | |
| Alternative Title | Investigation of η phase and σ phase’s transformation in several Nickel based superalloys and Re’s effect on solidification behavior |
| 龙飞 | |
| Subtype | 硕士 |
| Thesis Advisor | 金涛 |
| 2008-12-23 | |
| 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 | 镍基高温合金 Η相 Σ相 Am3合金 Re元素 |
| Abstract | 本文包括以下主要内容：基于GTD111和IN738合金成分分别设计了三种成分略有差别的DK3、DK4和DK5多晶合金，研究了化学成分对合金组织和力学性能的影响；合金DK5中σ相和η相在铸造过程中的形成机制；合金DK3中η相在热处理过程中的析出机制；以及Re元素添加对AM3高温合金定向凝固行为的影响。 鉴别了三种多晶合金铸态组织中的微量相，发现合金DK3共晶边缘生成条块状η相，合金DK4和DK5共晶边缘生成条块状η相和粒状σ相。枝晶间高的Ti/Al比使铸态η相的形成倾向增加。当合金化学成分中（Ti+Al）值较大时，不规则粒状σ颗粒将在共晶边缘形成。 对DK3、DK4和DK5合金进行了1100℃2小时加843℃6小时的热处理。发现在固溶处理过程中，在合金DK3中共晶区域发生γ′→η相相变，η相在共晶冠内富Ti的粗大γ′颗粒内形核，并以片状形貌向共晶内部生长；在合金DK4和DK5中，铸态存在的粒状σ相转变为γ相，并呈现锯齿状的σ/γ相变界面。热暴露过程中，合金DK3中γ′→η相相变继续发生，并伴随着M23C6颗粒在η相相界处生成；合金DK4和DK5中在枝晶间区域发生大量的片状σ相析出。在铸态存在的粒状σ相导致合金DK4和DK5的组织不稳定，由粒状σ相转变得到的γ相为片状σ相的沉淀析出提供了形核位置。三种合金拉伸力学性能受枝晶间微量相的影响，在合金DK3微观组织中存在的块状或片状η相降低了其拉伸强度。而在合金DK4和DK5由于无片状η相在热处理过程中形成，它们具有与对比合金GTD111相当的拉伸强度。 通过透射电镜观察对合金DK5中铸态形成的粒状σ相和条块状η相进行了观察。发现粒状σ相与γ相无晶体学取向关系，判断其形核位置应为凝固结束阶段的残余液相，其长大机制可能与准晶相在快速凝固过程中的长大机制相同，通过吸附原子团簇长大。η相具有规则块状形貌，且与γ相存在明显的晶体学取向关系，其形成过程应为在凝固结束后从富Ti的枝晶间区域的固态沉淀析出过程。 对合金DK3固溶处理过程中η相相变机制进行了研究。发现η相在γ′相内层错上形核，并通过超不全位错的滑移生长。η相与γ′相存在{0001}η//{111}γ′, η//[110]γ′的晶体学取向关系。两相在相界面处共有一层原子，相界为半共格界面。合金元素Hf，Ti在Ni3Al晶体结构中的引入降低了γ′相层错能，促进了γ′→ η相变的发生。 在AM3合金中添加了不同含量的Re元素，经定向凝固后，对铸态金相组织及元素偏析进行了定量分析。发现Re元素的添加加剧了元素Al、Ti、Ta和W等的显微偏析，化学成分中Re元素含量越高，合金中元素的显微偏析越严重。定向凝固AM3合金的一次枝晶间距由提拉速率决定，提拉速率越快，一次枝晶间距越小。添加Re元素对一次枝晶间距无明显影响。共晶体积分数随提拉速率和Re含量的增加而增加，Re元素的添加对共晶体积分数的影响更加明显。 |
| Other Abstract | Two kind of nickel based superalloys were chosen for the investigation of their phase transformation and solidification behavior in this dissertation. The first alloys were three polycrystalline superalloys DK3, DK4 and DK5, which were derived from the chemical composition of GTD111 alloy and IN738 alloy. The second alloys were directional solidified AM3 alloy and AM3 alloys with different Re additions. The microstructures and tensile mechanical properties of the three DK alloys had been investigated. Quantitive analysis were done to measure the microsegregation and as-cast microstructure of AM3 alloy and Re containing AM3 alloys. The minor phases in the as-cast microstructures of DK alloys had been indentified. Platelet like η phase existed near eutectics in alloy DK3, while both platelet like η phase and nodular like σ phase existed near eutectics in alloy DK4 and DK5. It was found that big Ti/Al ratio in the interdendritic region would favor the formation of η phase during the casting process. When the (Ti+Al) value in the chemical composition of the alloy was big enough, nodular σ phase would form coupled with η phase near eutectics during casting. Alloy DK3, DK4 and DK5 had been heat treated with the procedure of 1100℃/2h plus 843℃/6h. During solution treatment, γ′→η phase transformation happened in the eutectics of alloy DK3. η phase nucleated from the Ti rich coarse γ′ in the eutectic periphery, and grew with plate like morphologies towards into the eutectics. In alloy DK4 and DK5, the nodular σ phase transformed into γ phase during solution treatment, the interfaces between the nodular σ phase and γ phase were of serrated like characteristic. When thermo exposed the heat treated alloys at 850℃, γ′→η phase transformation continued in alloy DK3, which accompanied with formation of M23C6 particles at the η phase boundary. Extensive σ phase precipitation happened in the interdendritic region of alloy DK4 and DK5 during thermo exposure. The γ phase which formed from nodular σ phase acted as nucleation sites for the precipitation of plate like σ phase during thermo exposure. Platelet like η phase decreased the tensile properties of alloy DK3 while nodular σ phase didn’t have obvious impact on tensile properties of alloy DK4 and DK5. The formation mechanism of the nodular σ phase and η phase which existed in the as-cast microstructure of alloy DK5 had been analyzed by SEM and TEM observation. It was found that nodular σ nucleated and grew directly from the liquids, because no orientation relationship existed between nodular σ and γ phase. The σ phase might have grown by trapping of atom clusters from its surrounding liquid, which was similar with the growth mechanism of quasicrystals during rapid solidification. The η phase had regular platelet morphology and definite orientation relationship with γ phase, which indicated that it precipitated from solid during cooling process. The phase transformation mechanism of γ′→ η phase in alloy DK3 during solution treatment was studied by TEM observation. It was found that η phase nucleated from the stacking faults in γ′ phase, and grew with plate like morphology by slippling of superpartial dislocations in γ′. The η phase had certain orientation relationship with γ′ phase, which was {0001}η//{111}γ′, η//<110>γ′. The phase interface between η phase and γ′ phasse was semicoherent, two phases shared one layer of atoms at their interface. Introducing of alloying elements of big atom sizes such as Ti and Hf decreased the stacking faults energy of γ′, which promoted the phase transformation of γ′→ η. AM3 alloy and AM3 alloys added with different Re had been directional solidified under different withdrawal rates. Quantitive analysis of partition coefficients of major alloying elements showed that addition of Re aggravated the segregation of alloying elements. The higher content of Re in the chemical composition, the more severe of the alloying elements’ partition will be. The value of primary dendrite arm spacing is determined by the solidification rate, which decreases with the increase of solidification rate. Re addition does not have any effect on the value. As-cast eutectic fraction levels increases with both nominal Re content and withdrawal rate, but Re has more apparent impact on the eutectic fraction than withdrawal rate. |
| Pages | 66 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.imr.ac.cn/handle/321006/17192 |
| Collection | 中国科学院金属研究所 |
| Recommended Citation GB/T 7714 | 龙飞. 几种镍基高温合金η相和σ相变及Re对凝固行为影响研究[D]. 金属研究所. 中国科学院金属研究所,2008. |
| Files in This Item: | There are no files associated with this item. | |||||
Items in the repository are protected by copyright, with all rights reserved, unless otherwise indicated.
Edit Comment