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Subsolidus ternary phase relationships in the systems FeAlO and CuAlO are reviewed in order to provide a basis for thermodynamic analysis of aluminate formation at Fe/α-Al2O3 and Cu/α-Al2O3 interfaces. Expressions for the critical oxygen activity in the Fe-rich and Cu-rich solid solutions necessary to stabilize the equilibrium aluminate phases (FeAl2O4 and CuAlO2, respectively) in the presence of α-Al2O3 are derived using data available in the literature. As in previous work in the NiαAl2O3 system, aluminate formation by solid state reaction of Fe and Cu with α-Al2O3 was calculated to require a threshold concentration of oxygen in the metal, which is of the order of 1/5 the solubility limit. The sults are presented in stability diagrams and compared with previous results on the Ni/α-Al2O3 system in terms of the free energies of formation of the aluminates and the relative free energes of solution of oxygen in the metals. The results are also compared with available experimental observations on Fe/α-Al2O3 and Cu/α-Al2O3 interfaces. 相似文献
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Fracture and fatigue experiments have been conducted on liquid phase bonded (LPB) and solid-state bonded (SSB) aluminum-alumina
interfaces. The LPB interfaces contain voids and dendritic FeAl3 precipitates, whereas SSB interfaces are relatively defect-free. These precipitates result in local embrittlement, yet both
interfaces are strong and tough. Upon cyclic loading, mode 1 cracks in both systems grow alternately along the interface and
within the Al. The development of a tortuous crack path elevates the apparent fatigue threshold through crack closure. Under
mixed mode loading, fatigue cracks approaching SSB interfaces propagate through the Al rather than along the interface. Conversely,
for LPB interfaces, mixed mode cyclic crack growth along the interface occurs in preference to propagation in the Al. Correlation
between the striation spacing and the crack tip opening displacement suggests a growth mechanism based on crack tip blunting.
A.G. EVANS, Professor, formerly with the Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138 相似文献
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Fracture and fatigue experiments have been conducted on liquid phase bonded (LPB) and solid-state bonded (SSB) aluminum-alumina
interfaces. The LPB interfaces contain voids and dendritic FeAl3 precipitates, whereas SSB interfaces are relatively defect-free. These precipitates result in local embrittlement, yet both
interfaces are strong and tough. Upon cyclic loading, mode 1 cracks in both systems grow alternately along the interface and
within the A1. The development of a tortuous crack path elevates the apparent fatigue threshold through crack closure. Under
mixed mode loading, fatigue cracks approaching SSB interfaces propagate through the A1 rather than along the interface. Conversely,
for LPB interfaces, mixed mode cyclic crack growth along the interface occurs in preference to propagation in the A1. Correlation
between the striation spacing and the crack tip opening displacement suggests a growth mechanism based on crack tip blunting. 相似文献
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《Acta Metallurgica Materialia》1991,39(8):1915-1924
Interface microstructural development during solid state diffusion bonding of Ni to single-crystal α-Al2O3 has been studied by electron microscopy. Nickel aluminate spinel (NiAl2O4) interphase layers ∼ 1 μm thick formed under high vacuum bonding conditions. Very high vacuum (VHV) annealing caused the spinel to disappear, indicating that its stability depends critically upon the oxygen activity. High vacuum diffusion bonding utilizing initially oxygen-free Ni and oxygen-containing Ni established that spinel formation requires a threshold oxygen activity, and furthermore, that the source of the required oxygen can be oxygen initially dissolved in the Ni. Thermodynamic calculations confirm that the threshold oxygen level necessary to stabilize the spinel increases from 0.006 at.% (60 at.ppm) at 1273 K to 0.025 at.% (250 at. ppm) at 1663 K. Further analysis indicates the spinel exhibits a maximum thickness determined by the difference between the initial and threshold oxygen concentrations and the Ni thickness. Considering the solubility limit of oxygen in solid Ni, the spinel thickness is limited to ∼0.005 times the Ni thickness. The reaction is explored further in the context of diffusion path concepts with a calculated NiAlO phase diagram. 相似文献
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Wettability is an important phenomenon in the liquid phase sintering of silicon carbide (SiC) ceramics. This work involved a study of the wetting of SiC ceramics by two oxide systems, Al2O3 /Dy2O3 and Al2O3 /Yb2O3, which have so far not been studied for application in the sintering of SiC ceramics. Five mixtures of each system were prepared, with different compositions close to their respective eutectic ones. Samples of the mixtures were pressed into cylindrical specimens, which were placed on a SiC plate and subjected to temperatures above their melting points using a graphite resistance furnace. The behavior of the melted mixtures on the SiC plate was observed by means of an imaging system using a CCD camera and the sessile drop method was employed to determine the contact angle, the parameter that measures the degree of wettability. The results of variation in the contact angle as a function of temperature were plotted in graphic form which showed that the curves displayed a fast decline and good spreading. All the samples of the two systems presented final contact angles of 40° to 10° indicating their good wetting on SiC in the argon atmosphere. The melted/solidified area and interface between SiC and melted/solidified phase were evaluated by scanning electron microscopy (SEM) and their crystalline phases were identified by X-ray diffraction (DRX). The DRX analysis showed that Al2O3 and RE2O3 reacted and formed the Dy3Al5O12 (DyAg) and Yb3Al5O12 (YbAg) phases. The results indicated that the two systems had a promising potential as additives for the sintering of SiC ceramics. 相似文献
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S. Nourbakhsh H. Margolin F. L. Liang 《Metallurgical and Materials Transactions A》1989,20(10):2159-2166
Pressure castings of Ni3Al(IC218)/Al2O3 and Ni/Al2O3 composites, made with continuous DuPont FP α-Al2O3 and DuPont PRD166 α-Al2O3+20 wt pct partially stabilized ZrO2 20 μm diameter fibers, were examined by optical, scanning electron microscope (SEM), and transmission electron microscope
(TEM) techniques. According to optical magnifications, excellent infiltration took place. However, in SEM and TEM magnifications,
small gaps were found adjacent to regions where bonding had taken place between fibers. On the basis of available evidence,
the gap formation was attributed to trapped gases and microshrinkage. Titanium was added to the metal to promote infiltration.
Diffusion of Ti into the fibers of the Ni/Al2O3 composites occurred, but similar diffusion into the fibers of the IC218/Al2O3 composites did not take place. The qualitatively higher bond strength of the interfaces of the Ni/Al2O3 composites was ascribed to the diffusion of Ti into Al2O3. No interface reaction layer was found in any of the composites. Very little grain growth was found to take place in either
the FP or PRD 166 fibers after casting and after a subsequent ten day anneal at 1150 °C. 相似文献
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We studied the reactions of Ti and Zr with AlN, 99.8% Al2O3 and 95% Al2O3. The substrates were chosen to represent a simple nitride (AlN), a simple oxide (99.8% Al2O3), and a simple oxide with a silicate grain boundary phase (95% Al2O3). The activities of the Ti and the Zr were varied by dissolving them at 1 and 5 wt% in the 72 Ag-28 Cu eutectic composition, which is otherwise unreactive with the ceramics. Reactions were studied by measuring the variation of the alloy contact angle on the ceramic with time at temperature and by determining the compositions of interfacial reaction products. Contact angles were lower for Ti alloys than for those containing Zr. Reaction products were primarily the nitrides of Zr and Ti for reaction with AlN and the respective oxides for reaction with Al2O3. Complex alloy phases were found in the metal away from the ceramic-metal reaction zone. 相似文献
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应用热压技术制备了添加不同含量Cr3C2和(W,Ti)C的Al2O3/Cr3C2/(W,Ti)C复合陶瓷材料。利用光学显微镜、环境扫描电镜、透射电镜和能谱分析仪等对~203/30%Cr3C2、Al2O3/30%(W,Ti)C、Al2O3/20%Cr3C2/10%(W,Ti)C三种复合陶瓷材料的显微组织结构进行了观察分析。研究表明:同其它两种材料相比,Al2O3/20%Cr3C2/10%(W,Ti)C陶瓷复合材料组织细化均匀,有连续骨架结构生成。Cr3G和(W,Ti)C颗粒的共同加入有利于晶粒生长的制约,裂纹分枝与偏转、晶粒拔出、以及纳米相等等,有效提高了氧化铝陶瓷材料的力学性能。 相似文献
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Nd2O3 was used to support Al2O3 and ZnO to prepare a supported solid base catalyst and investigate the effect of catalyst and reaction conditions on the synthesis of tert-butyl acetate. The composited oxide of Nd2O3/Al2O3-Nd2O3/ZnO exhibited excellent catalytic activity for the synthsis of tert-butyl acetate. The molar ratio of tert-butanol to acetic anhydride is 31, the catalyst in total amount of reactant nearly 0.5%, and reaction time 6 h. With the above conditions, yield of the reaction could reach to 65%. The structure of product were verified by the FT-IR, Element analysis, and MS, which proved that the product was tert-butyl acetate. 相似文献
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采用喷射沉积和内氧化法制备出Al2O3La2O3Y2O3/Cu复合材料,研究该材料在直流20 V/20 A的工作条件下触点的电弧侵蚀特性,并与Al2O3/Cu材料进行了对比分析.利用电子天平、扫描电镜等方法分析电弧侵蚀后触点的质量变化和表面微观结构.结果表明,通过添加Y2O3、La2O3稀土氧化物颗粒,可有效降低触头材料的材料转移量.Al2O3La2O3Y2O3/Cu材料的抗熔焊性和抗烧损性优于Al2O3/Cu材料的性能.在直流阻性负载条件下Al2O3La2O3Y2O3/Cu阳极触头表面形成凹坑,阴极触头表面形成凸起,触点表面显示出浆糊状凝固物和喷发坑等电弧侵蚀形貌特征. 相似文献
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本研究采用高温氧化的方法制备出纳米NiAl2O4/Al2O3粉体。在纳米Al2O3粉体表面包覆一层金属Ni,在1350℃高温下焙烧Ni/Al2O3复合粉体得到纳米NiAl204/Al2O3粉体。利用TEM对Ni/Al2O3复合粉体进行观察,发现Ni/Al2O3复合粉体颗粒成球形,大小为50~60nm;通过对Ni/Al2O3复合粉体的DTA析,显示Ni/Al2O3复合粉体在900℃和1300℃下有新相生成,经XRD检测,新相分别为NiO和NiAl2O4。 相似文献
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Bing Zhou Quanli Ke Meijun Wen Tianbiao Ying Guokai Cui Ying Zhou Zhenyu Gu Hanfeng Lu 《中国稀土学报(英文版)》2023,41(8):1171-1178
CeO2,La2O3,and CeO2-Y2O3 oxides were coated on the surface of spherical granular AI2O3(3-5 mm)through impregnation method,and proved as better supports of Pd and Pt catalysts.The influences of rare earth metal doping on the adsorption rates of Pd and Pt ions,as well as the catalytic performance,were investigated.Results show that the H2PtCl6·6H2O adsorption rates of the Al 相似文献