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.     

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.     

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.     

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.     

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.     

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。     

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。     

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。     

In-situ high temperature X-ray diffraction study of Fe/Al2O3 interface reactions

In-situ experiments on the Fe/Al2O3 interface reaction were carried out with a high temperature X-ray diffractometer capable of measuring the X-ray diffraction pattern in 1–4s, using an imaging plate. The kinetic formation processes of the interface reaction layer were measured in short-period exposure experiments using the apparatus. The time-temperature phase diagram of Fe/Al2O3 in air was determined. Fe/Al2O4 was formed at the FeAl2O3 interface between 1595 K and 1675 K in air. The formation of FeAl2O4 obeyed the parabolic rate law. The value of the activation energy suggests that the diffusion of Al into FeAl2O4 controls the rate of formation. The results of thermal expansion coefficient measurements suggest that when a sample is cooled to room temperature, compressive strain caused by FeAl2O4 occurs on Al2O3.     

Influence of surface modification of alumina on bond strength in Al2O3/Al/Al2O3 joints

The subject of the work was to study the effect of Ti thin film on alumina ceramic on mechanical strength and fracture character of Al₂O₃/Al/Al₂O₃ joints. The joints were formed by liquid state bonding of alumina substrates covered with titanium thin film of 800 nm thickness using Al interlayer of 30μm thickness at temperature of 973 K in a vacuum of 0.2 mPa for 5 min. The bend strength was measured by four–point bending test at room temperature. Scanning and transmission electron microscopy were applied for detailed characterization of interface structure and failure character of fractured joint surfaces. Result analysis has shown that application of the Ti thin film on alumina leads to decrease of bond strength properties of Al₂O₃/Al/Al₂O₃ joints along with the change either of structure and chemistry of interface or of failure character.     

原位热压合成Ti3AlC2/Al2O3复合材料的研究

以Ti,Al,Tic,TiO2粉末为原料,采用原位热压合成法制备了Ti3AlC2/Al2O3复合材料.主要考察不同Al2O3含量对复合材料性能的影响.在1 400℃,30 MPa压力,保温2 h条件下烧结制得致密的Ti3Alc2/Al2O3块体材料.采用XRD分析了不同Al2O3,含量的复合材料的相组成.用SEM观察组织结构特征.测量了维氏硬度和电导率同Al2O3含量的关系曲线.研究结果表明,A12O3,的加入可大幅度提高复合材的硬度.Ti3AlC2/25%A12O3的维氏硬度可达8.7 GPa.虽然添加Al2O3后复合材料的电导率有所下降,但Al2O3对复合材料强度和硬度的增加有显著的贡献.Ti3Al2C2/Al2O3乃不失为一种性能良好的高温结材材料.     

Eutectic solidification in the system Al2O3/Y3Al5O12

The eutectic solidification in the system Al₂O₃/Y₂Al₅O₁₂ has been investigated. A Bridgman-type crystal-growing furnace was used in this investigation. A temperature gradient of 190° C/cm and growth rates which were varied between 2 and 12 cm/h were employed in the directional solidification studies. Three types of microstructure were observed depending upon the composition and the growth rate. At a growth rate of 4 cm/h and at compositions removed from the eutectic composition, a mixture of primary phase and fine eutectic dispersion was found. At growth rates between 2 and 12 cm/h at the eutectic composition, a colony type microstructure was most commonly observed. At growth rates above 4 cm/h at the eutectic composition, regions in the solidified ingot were found to have a highly oriented eutectic microstructure consisting of both rods and platelets. These eutectic microstructures indicate that coupled growth can occur in this system. The method of Sunquist and Mondolfo [15] was used to determine whether Y₃Al₅O₁₂ was the first phase to nucleate at the eutectic.     

Al/Al2O3陶瓷接合基板的制备及性能研究

在675～825°C、氮气气氛下,使用石墨模具压铸的方法制备出Al/Al2O3电子陶瓷基板,利用力学拉伸试验机测试了Al和Al2O3的结合强度,界面抗拉强度＞15.94MPa,使用金相显微镜、SEM等微观分析仪器研究了其界面的微观结构.