Juan Hou

Interfacial precipitation of the M5B3-type boride in Ni-based superalloys

Abstract Microstructural characteristics of an experimental Ni-based superalloy with boron addition subjected to a long-term ageing treatment were systematically investigated by various kinds of transmission electron microscopy technique. Based on detailed electron diffraction analyses, we found that there are many nanosized M5B3 precipitates in our long-term ageing alloys, which keeps a good orientation relationship with the γ/γ′ matrix. Furthermore, the precipitation characteristics of M5B3 phase were clarified. It is found that the M5B3-type boride prefers to precipitate at the γ/γ′ interfaces and low-angle grain boundaries. These interfacial nanosized precipitates can play the role of pinning effect and are expected to be advantageous for postponing the γ′ rafting and low-angle grain boundary migration to some extent at high temperature.

Microstructural characterization of the M23C6 carbide in a long-term aged Ni-based superalloy

Abstract The microstructural features of M23C6 carbide in a long-term aged heat- and corrosion-resistant Ni-based superalloy have been investigated in detail using various kinds of transmission electron microscope (TEM) techniques. It is found that TEM contrast, which is related to structural and chemical inhomogeneities inside the grains, always exists in the interior of grains in the alloy. The structure of these inhomogeneous regions has been determined to be the same as that of the γ′ and t-M23C6 phases, where t-M23C6 indicates a transitional and metastable phase. Although possessing the same structure as the M23C6 phase, the chemical composition of the t-M23C6 is different from that of the M23C6 phase. Compared with M23C6, t-M23C6 is richer in Ni, Co, Al and Ti but poorer in W, Mo and Cr. This phenomenon of structural and chemical inhomogeneity demonstrates that pristine M23C6 carbide (p-M23C6) precipitated in standard heat-treated samples is unstable. Therefore, upon long-term ageing treatment, Ni, Co, Al and Ti may locally enrich inside the p-M23C6 phase, finally forming the γ′ phase, which can be described by the decomposition reaction p-M23C6 → M23C6 + γ′.

Microstructural characterization of the η-Ni3(Ti, Al) phase in a long-term-aged Ni-based superalloy

Abstract Microstructural features of a geometrically closed packed hexagonal η-Ni3(Ti, Al) phase precipitated in a long-term-aged Ni-based superalloy are characterised using various kinds of transmission electron microscope (TEM) techniques. The defect features in the η grain interior are clearly revealed at the atomic scale. A nano-sized γ′ phase is found at the defect regions of the micro-sized η phase. The interior γ′ phase keeps a good orientation relationship (OR) of (1 1 1)γ′//(0 0 0 1)η and [1 0]γ′//[2 0]η with the η-Ni3(Ti, Al) phase. However, there is no definitive OR between η-Ni3(Ti, Al) grains and the surrounding matrix. By means of first-principle calculations, we reveal that a symmetrical interfacial feature between γ′ and η corresponds to a lower energy state.

One-step Self Assemble of Cu-TiO 2 Heterogeneous Nanoparticles Using a Soft Template: One-step Self Assemble of Cu-TiO 2 Heterogeneous Nanoparticles Using a Soft Template

以聚乙二醇(PEG)为软模板剂, 采用一步水热法合成了具有异质结构的铜–二氧化钛复合纳米粒子. 利用X射线衍射谱(XRD)、透射电子显微镜(TEM)等分别对制备材料的相组成、微观结构进行了研究. 结果表明, 一步水热法制备的异质纳米粒子由单一立方相铜和锐钛矿相二氧化钛组成. 高分辨透射电子显微镜(HRTEM)在单一粒子中观测到清晰的铜(101)和二氧化钛(111)晶面构成的界面. 该界面有助于二氧化钛光生电子–空穴对的分离. 同时, 所制备纳米粒子的颗粒尺寸和光吸收特性可以通过改变PEG分子链长进行微调. 本研究还对水热过程的反应机理进行了讨论, 结果表明: PEG与铜氨络合物通过氢键连接, 其链长对于粒子尺寸的影响在于PEG对Cu颗粒的尺寸进行的调节, 而此过程中二氧化钛的晶粒尺寸并无明显变化. 紫外–可见吸收光谱表明该异质纳米粒子与普通二氧化钛纳米粉体相比, 对可见光区光谱有较为强烈的吸收. 该界面纳米材料是一种有潜在应用价值的光催化材料和太阳能电池材料.Cu-TiO2 heterostructure nanoparticles were successfully synthesized via a novel one-step self-assemble hydrothermal method using polyethylene glycol as the soft template. The nanospheres were characterized in light of the chemical composition and morphology using X-ray diffraction (XRD) and transmission electron microscope (TEM), respectively. The products are composed of cubic copper and anatase TiO2. Interfaces between Cu (101) and TiO2 (111) were observed by HRTEM. In addition, the nanoparticles size could be controlled by adjusting the polymerization degrees of PEG. The accommodations of the particle sizes were mainly caused by Cu nanospheres rather than TiO2. A possible synthetic mechanism which interprets the formation of Cu-TiO2 heterogeneous nanoparticles could be ascribed to the hydrogen bonds between Cu(NH3)(2)(+) and PEG. UV-Vis absorption spectra indicated that the prepared product has strong absorbency in the visible region. Therefore, the unique interface nanomaterial could be used as a potential class of the materials platform as visible-light-driven photocatalyst and electrode on enhancing the photoelectric properties of solar cells.以聚乙二醇(PEG)为软模板剂, 采用一步水热法合成了具有异质结构的铜–二氧化钛复合纳米粒子. 利用X射线衍射谱(XRD)、透射电子显微镜(TEM)等分别对制备材料的相组成、微观结构进行了研究. 结果表明, 一步水热法制备的异质纳米粒子由单一立方相铜和锐钛矿相二氧化钛组成. 高分辨透射电子显微镜(HRTEM)在单一粒子中观测到清晰的铜(101)和二氧化钛(111)晶面构成的界面. 该界面有助于二氧化钛光生电子–空穴对的分离. 同时, 所制备纳米粒子的颗粒尺寸和光吸收特性可以通过改变PEG分子链长进行微调. 本研究还对水热过程的反应机理进行了讨论, 结果表明: PEG与铜氨络合物通过氢键连接, 其链长对于粒子尺寸的影响在于PEG对Cu颗粒的尺寸进行的调节, 而此过程中二氧化钛的晶粒尺寸并无明显变化. 紫外–可见吸收光谱表明该异质纳米粒子与普通二氧化钛纳米粉体相比, 对可见光区光谱有较为强烈的吸收. 该界面纳米材料是一种有潜在应用价值的光催化材料和太阳能电池材料.