Ti/Al2O3复合材料性能研究

本文利用放电等离子烧结技术制备了致密的Ti/Al2O3复合材料.实验结果表明,60vol%Al2O3和80vol%Al2O3的Ti/Al2O3复合材料,界面处生成少量的TiAl,使得Ti与Al2O3间的界面能大于其单个晶粒的界面能,复合材料性能随Ti含量的增加而增大;40vol%Al2O3和20vol%Al2O3的Ti/Al2O3复合材料,界面处生成脆性的Ti3Al相,使得Ti与Al2O3间的界面能小于各自晶粒的界面能,材料的性能随Ti含量的增加而降低,同时断裂的模式也发生改变,由穿晶断裂为主转变为沿晶断裂,脆性的Ti3Al相是Ti/Al2O3复合材料力学性能降低的主要原因.     

Ti/Al2O3复合材料制备及其力学性能

利用放电等离子烧结(SPS)制备了性能优异的40%(体积分数)Ti/Al2O3复合材料,其弯曲强度、断裂韧性、显微硬度和相对密度分别为897.29MPa、17.38MPa·m1/2、17.13GPa和99.24%.SEM和HREM对复合材料的微观结构分析发现,晶粒细化、位错环强化等是材料强度提高的主要原因;裂纹的偏转和桥联是材料韧性提高的关键所在.     

Al2O3/Ti3SiC2层状复合材料的制备与性能

采用两种方法制备Al2O3／Ti3SiC2层状复合材料，一是原位-热压法，即Ti3SiC2是在层状材料的制备过程中同时被合成的；一是分步法，即制备过程分两步进行，首先制备出Ti3SiC2高纯粉，再采用热压法进行烧结制备层状材料。两种方法制备的Al2O3／Ti3SiC2层状复合材料强度保持在450MPa以上，断裂功达到1200-1560J／m^2，相对Al2O3块体材料提高十余倍。另外，不同的制备方法得到不同的组成和显微结构，决定了这两种Al2O3／Ti3SiC2层状复合材料性能的差异：前者强度较高韧性较低，后者强度较低而韧性较高。     

Synthesis of Ti3AlC2/Al2O3 nanopowders by mechano-chemical reaction

Ti₃AlC₂/Al₂O₃ nanopowders were synthesized by the combination of mechanically-induce self-propagating reaction (MSR) of Ti, C, Al and TiO₂ powder mixtures and subsequently heat treatment. Effects of high energy milling and heat treatment temperatures on the phase transformation were investigated in detail. X-ray diffraction (XRD) was used to characterize the powders of milled and annealed, respectively. The morphology and microstructure of as fabricated products were also studied by scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS). Results show that TiC, Ti_xAl_y and Al₂O₃ transitional phases were formed when the initial powder mixtures were milled for 24 h. The desired Ti₃AlC₂/Al₂O₃ nanopowders with high purity were obtained when annealed the as-milled powders at 1100 °C. SEM image confirmed that the as fabricated Ti₃AlC₂/Al₂O₃ particles has nanocrystalline layered structural matrix of Ti₃AlC₂, and the second phase of nanosized Al₂O₃ disperses uniformly in the Ti₃AlC₂ matrix.     

Interfacial reactions in K2Ti6O13(w)/Al2O3/Al composite

Abstract

A pure Al matrix composite, reinforced by potassium titanate whiskers coated with sol–gel alumina, was fabricated by squeeze casting. Good interface bonding was achieved in the coated composite. Interfacial reactions in the composite were found to be less severe than those in an uncoated composite, owing to the barrier effect of sol–gel -Al₂O₃ coating. After the composite was thermally exposed at 530°C for 30 h, the alumina coating still restrained the decomposition of the whisker structure, and thus prevented a decrease in the strength of the composite. However, after a thermal exposure at 700°C for 10 h, the coating was no longer held on whisker surfaces. Mechanical testing showed that tensile fracturing of the coated composite tended to occur at the coating/matrix interface where the interfacial bonding is weaker than at the coating/whisker interface.     

Development and Characterization of Al2O3 Dispersed Al/Mg/Cu/Ti Matrix Composite

The effect of dispersion with different weight fractions of Al2O3 particles in metallic matrices （AI/Mg/Ti/Cu） fabricated by powder metallurgy was investigated. In the case of 15 wt% Al2O3 reinforced composites, peak hardness was attained which subsequently decreased with increasing the content of Al2O3. A correlation between the microhardness and nanomechanical properties at submicron scale was examined for all the composites. Specific strength and specific modulus were measured in order to figure out the performance of the composites.     

Mechanically activated combustion synthesis of Ti3AlC2/Al2O3 nanocomposite from TiO2/Al/C powder mixtures

Ti₃AlC₂/Al₂O₃ nanocomposite powder was synthesized by mechanical-activation-assisted combustion synthesis of TiO₂, Al and C powder mixtures. The effect of mechanical activation time of 3TiO₂-5Al-2C powder mixtures, via high energy planetary milling (up to 20?h), on the phase transformation after combustion synthesis was experimentally investigated. X-ray diffraction (XRD) was used to characterize as-milled and thermally treated powder mixtures. The morphology and microstructure of as-fabricated products were also studied by scanning electron microscopy (SEM) and field-emission gun electron microscopy (FESEM). The experimental results showed that mechanical activation via ball-milling increased the initial extra energy of TiO₂-Al-C powder mixtures, which is needed to enhance the reactivity of powder mixture and make it possible to ignite and sustain the combustion reaction to form Ti₃AlC₂/Al₂O₃ nanocomposite. TiC, AlTi and Al₂O₃ intermediate phases were formed when the initial 10?h milled powder mixtures were thermally treated. The desired Ti₃AlC₂/Al₂O₃ nanocomposite was synthesized after thermal treatment of 20?h milled powder and consequent combustion synthesis and FESEM result confirmed that produced powder had nanocrystalline structure.     

In situ synthesis and characterization of a hierarchically structured Al2O3/Al3Ti composite

A hierarchically structured α-Al₂O₃/Al₃Ti composite was fabricated by an in situ process called exothermic dispersive synthesis from a powder blend of Al and TiO₂. The microstructure of the composite was investigated by X-ray diffraction, scanning electron microscopy, and X-ray energy dispersive spectroscopy. Three transitional phases, specifically TiO, Ti₂O₃, and γ-Al₂O₃, were found to form during the reactive process. Using differential scanning calorimetry, it was found that the reaction between the Al and TiO₂ occurred through three intermediate steps and their corresponding activation energies were 390, 205, and 197 kJ/mol, respectively. Moreover, the reaction rate of the third step was found to be much higher than that of the second step, and the time taken by each reaction step decreased with the increase of the heating rate. The findings are critical to understanding the microstructural development in the synthesis of strong and tough Al₂O₃/Al₃Ti composites.     

Al2O3/Al2O3 Joint Brazed with Al2O3-particulate-contained Composite Ag-Cu-Ti Filler Material

1.IntroductionTo improve the mechanical properties and relieve mis-matches between the filler metals and base materials,the particulates of superalloys,ceramic or carbon fiberswere added into the conventional brazing filler metal toform composite filler material.The method has beenused in aero-engine component repairing[1,2],fine castcomponent joining[3],wide clearance butt jointing[4],ce-ramic brazing[5,6]and electronic package[7].However,the method was used mostly in metal brazing.The mi-cro…     

Slip casting of Al2O3 and Al2O3/ZrO2 composites

Al₂O₃ and Al₂O₃/ZrO₂ composites have been fabricated by slip casting from aqueous suspensions. The physical and structural characteristics of the starting powders, composition of the suspensions, casting behaviour, microstructure of the green and fired bodies and the mechanical properties of the products were investigated. The addition of ZrO₂ to Al₂O₃ leads to a significant increase in fracture toughness when ZrO₂ particles are retained in the tetragonal form (transformation-toughening mechanism) but when microcracking (due to the spontaneous transformation of ZrO₂ from the tetragonal phase to the monoclinic one) is dominant, an excellent toughness value is accompanied by a drastic drop in strength and hardness.     

Ti/Al2O3 Functionally Gradient Material Prepared by the Explosive Compaction/SHS Process

1.IntroductionDistinctinterfacesoccurincompositesorasare-sultofthefabricationprocessasincoatingandbond-ing.Thepresenceofadistinctillterfacecanleadtoproblemsduringfabricationorserviceuse.Forexam-ple,delaminationorcrackingalongabondinglayerformetal-ceramiccompositemayoccurasaresultofmechanicalstressesorthermalstressesthataredevelopedfromthedifferenceinthermalexpansionbetweenmaterialsifthebondinglayerissubjectedtotemperaturevariation[1].Therecentdevelopmentintheprocessingoffunctionallygradientmat…     

Al_2O_3/Al复合材料型内处理成型工艺研究

论述了Ａｌ２Ｏ３（ｐ）／Ａｌ复合材料型内处理成型工艺，并讨论了影响复合区域凝固过程的有关因素，指出了控制复合区域内Ａｌ２Ｏ３粒子的分布的途径。     

XRCT characterisation of Ti particles inside porous Al2O3

Computed X-ray tomography was used to characterise distribution and sphericity of Ti granules within highly porous (> 35%) Al₂O₃ powder compacts, as they are key parameters for a successful infiltration by Fe-based alloys. Setting of reconstruction constraints, image editing as well as data processing are the most challenging parts of computed X-ray tomography and principal sources of errors that bias the generated data. Thus, corrective measures have to be applied and the reliability of generated data has to be proved with respect to statistical, stereological and volumetric aspects. Combining an adapted Interface Particle Treatment Algorithm with the Marching Cube Method, Equilibrium Random State Model, cluster splitting and conventional laser diffraction measurements a significant improvement of the three-dimensional reconstructed data was achieved. This study points out the need of the applied algorithms for the proof and improvement of generated data by computed X-ray tomography and gives a short survey of methods that can be applied.     

Comparative study of the luminescence of Al2O3:Ti and Al2O3 crystals under VUV synchrotron radiation excitation

The comparative study of the luminescent properties of Al₂O₃:Ti crystal in comparison with those for undoped Al₂O₃ crystal counterpart is performed under synchrotron radiation excitation with an energy of 3.7–25 eV. Apart from the main emission band peaked at 725 nm related to the ²E → ²T₂ radiative transitions of Ti³⁺ ions, the luminescence of excitons localized around Ti ions in the band peaked at 290 nm and the luminescence of F⁺–Ti and F–Ti centers in the bands peaked at 325 and 434 nm are also found in the emission spectra of Al₂O₃:Ti crystal. We show also that the luminescence of Ti³⁺ ions in Al₂O₃:Ti crystal can be effectively excited by the luminescence of excitons localized around Ti dopant as well as by the luminescence of F–Ti centers.     

Optical properties of the Al2O3/SiO2 and Al2O3/HfO2/SiO2 antireflective coatings

Investigations of bilayer and trilayer Al₂O₃/SiO₂ and Al₂O₃/HfO₂/SiO₂ antireflective coatings are presented in this paper. The oxide films were deposited on a heated quartz glass by e-gun evaporation in a vacuum of 5 × 10^?3 [Pa] in the presence of oxygen. Depositions were performed at three different temperatures of the substrates: 100 °C, 200 °C and 300 °C. The coatings were deposited onto optical quartz glass (Corning HPFS). The thickness and deposition rate were controlled with Inficon XTC/2 thickness measuring system. Deposition rate was equal to 0.6 nm/s for Al₂O₃, 0.6 nm ? 0.8 nm/s for HfO₂ and 0.6 nm/s for SiO₂. Simulations leading to optimization of the thin film thickness and the experimental results of optical measurements, which were carried out during and after the deposition process, have been presented. The optical thickness values, obtained from the measurements performed during the deposition process were as follows: 78 nm/78 nm for Al₂O₃/SiO₂ and 78 nm/156 nm/78 nm for Al₂O₃/HfO₂/SiO₂. The results were then checked by ellipsometric technique. Reflectance of the films depended on the substrate temperature during the deposition process. Starting from 240 nm to the beginning of visible region, the average reflectance of the trilayer system was below 1 % and for the bilayer, minima of the reflectance were equal to 1.6 %, 1.15 % and 0.8 % for deposition temperatures of 100 °C, 200 °C and 300 °C, respectively.     

Ti3SiC2/SiC在Na3AlF6/Al2O3高温熔盐中的热腐蚀行为

研究了不同组成的Ti3SiC2／SiC复合材料在Na3AlF6／Al2O3高温（960℃）熔盐中的热腐蚀行为,从理论上进行了热腐蚀动力学分析,并通过XRD和SEM分析了腐蚀产物的成分、结构和形貌。结果表明,该材料能够长时间处于高温熔盐气氛中而不发生组织、结构的变化,在高温电解铝熔盐中具有优良的耐腐蚀性能,可以作为高温结构材料使用。     

Al2O3含量对Al2O3/W复合材料合成的影响

以铝热法为基础制备了A12O3/W复合材料，探讨了A12O3含量对复合材料合成的影响。研究表明：主要物相为α-A12O3、金属W。刚玉含量小于0．3时，温度影响不显著，大于0．3时，温度影响显著，有大量碳化物生成，且WC/W2C相对含量随A12O3含量增加及煅烧温度的提高而增加。当刚玉含量为0．5mol时，有正交晶钨酸铝生成。随刚玉含量变化，金属钨分布从连续分布向弥散分布变化。连续分布的金属钨因被氧化铝包裹因此难以碳化，而弥散分布的金属钨则易于被碳化。     

Microstructure of the Al2O3/Al2O3 Joint Brazed with Cu-Zn-Ti Filler Metal

Microstructure and interface reactions of Al2O3 joints brazed by Cu-Zn-Ti alloy were studied by using SEM, EDS and XRD. The effects of brazing temperature and Ti content on interfacial reactions and microstructure were investigated, and the action of adding Zn into brazing alloy was also studied. TiO, Ti3Al and CuTi were formed at the interface of ceramics and the filler metal, while CuTi, Cu3Ti and alpha -Cu were found in the brazing. The thickness of the reaction layer increased with increasing of brazing temperature, under the same brazing process, the thickness increased with the Ti content.     

Al/Al2O3多层膜的研究

用真空蒸镀及自然氧化方法在玻璃基底上制备纳米量级的4、5、6、7对层的Al／Al2O3多层膜。采用称重法测定薄膜的厚度；在常温和低温下使用三点法测定多层膜的电特性；用扫描电镜（sEM）观察薄膜的表面和截面的形貌及成分。结果表明：制备的是纳米量级非晶态的Al／Al2O3多层膜，在常温和低温（77K）下均具有类似负阻的特性。