Fe－40Al合金与Al2O3陶瓷的界面润湿现象

本文采用座滴法研究了金属间化合物Fe-40 Al与Al₂O₃陶瓷的润湿性及界面的相互作用,重点考察了温度、保温时间以及合金元素对Fe-40A1合金/Al₂O₃润湿行为和界面反应的影响。     

Deformation and damage in Al/Al2O3

Al/Al₂O₃-composites as an example of light weight materials are very interesting for many industrial applications because of a favourable combination of low density and improved mechanical properties. The prediction of the macroscopic mechanical behaviour of these materials related to their microstructure requires the knowledge of damage initiation and crack development under external loading conditions and, if present, residual stresses have to be taken into consideration. Different types of material degradation like particle/matrix-debonding, particle failure and matrix cracking can be observed in these types of metal matrix composites. The aim of the present work is to introduce damage criteria into a FE-microstructural model in order to foresee the degradation process in an Al₂O₃-particle reinforced Al(6061) composite during mechanical loading. Presently, the conventional fabrication route of the Al/Al₂O₃-composite is a metallurgical method with extrusion for homogenisation of the microstructure and final heat treatment to achieve a defined precipitation state. The influence of thermal residual stresses due to cooling down from annealing temperature on the deformation and damage initiation of Al(6061)/10vol%Al₂O₃-composites is investigated through finite element analyses using the experimentally mapped real microstructure as binary data. Especially, the stresses in the ceramic particles which are responsible for particle cracking and the hydrostatic stresses in the Al-matrix making the particle–matrix interface prone to debonding were analysed. The results show the importance of the thermal residual stresses with respect to damage criteria as obtained by micromechanical FE-calculations.     

Formation process of Al2O3 thin film by reactive sputtering

Al and Al₂O₃ films were deposited by RF magnetron sputtering using a mixed gas of Ar and O₂. The surface of the Al target was changed from the metallic mode to the oxide mode at a critical O₂ flow ratio of 8%. The atomic ratio of sputtered Al atoms to supplied oxygen atoms was found to be approximately 2:3 at the critical O₂ flow ratio. The oxide layer thickness formed on the Al target was estimated to be 5-7 nm at an O₂ flow ratio of 100% by ellipsometry.     

Al/Al2O3多层膜的表面和界面的分析研究

用热蒸发沉积和自然氧化及加热法制备纳米量级的Al/Al2O3薄膜和多层膜.用X射线光电子谱仪(XPS)和透射电镜(TEM)对样品进行检测.XPS实验说明自然氧化的Al2O3膜层厚在2～5 nm.Al/Al2O3薄膜及多层膜的O与Al的原子浓度比为1.43～1.85.Ar离子刻蚀的XPS实验结果(刻蚀速率为0.09 nm/s)说明2个对层的Al/Al2O3多层膜截面样品具有周期性结构.TEM观察到了5个对层的Al/Al2O3多层膜的层状态结构,其周期为4 nm.由此说明,热蒸发及自然氧化法是制备纳米量级的Al/Al2O3多层膜的有效方法.     

Mechanomaking of Fe/Al2O3 and FeCr/Al2O3 nanocomposites powders fabrication

Nanocomposite powders (Fe or Fe-Cr alloy)/-Al₂O₃ (75 and 85 vol.%) were obtained by room-temperature high-energy milling powder mixtures of hematite (and chromium oxide) with aluminum and alumina in a high-capacity mill for 8-10 h. The composition of iron and iron alloys was followed by Mössbauer spectroscopy, while the appearance of other phases was revealed by X-ray diffraction. The powder particles produced are assemblies of grains (10–20 nm in size) with a wide size distribution (from well below 1 μm up to several hundreds) and low porosity (fully dense particles). Both the metallic and ceramic phases have crystallite sizes below 15 nm for all the compositions investigated. Nano-nano type ceramic nanocomposites were, therefore, obtained.     

Bond strength and microstructure investigation of Al2O3/Al/Al2O3 joints with surface modification of alumina by titanium

Joints of Al₂O₃/Al/Al₂O₃ are formed by liquid-state bonding of alumina substrates covered with thin titanium film of 800 nm thickness using an Al interlayer of 30 or 300 μm at 973 K under a vacuum of 0.2 mPa for 5 min and an applied pressure of 0.01 MPa. The bond strength of the joints is examined by a four-point bend testing at room temperature coupled with optical, scanning and transmission electron microscopy. Results show that: (i) bonding occurs due to the formation of a reactive interface on the metal side of the joint with the presence of Al₃Ti precipitates (ii) a decrease in Al layer thickness leads to stronger Al₂O₃/Al/Al₂O₃ bonds accompanied by a change of both the distribution of reaction products (Al₃Ti) in the region of the interface and the failure surface characteristics.     

Hot deformation of ultrafine-grained Al6063/Al2O3 nanocomposites

Ultrafine-grained (UFG) Al6063 alloy reinforced with 0.8 vol% nanometric alumina particles (25 nm) was prepared by reactive mechanical alloying and direct powder extrusion. Transmission electron microscopy and electron backscatter diffraction analysis showed that the grain structure of the nanocomposite composed of nanosize grains (<0.1 μm), ultrafine grains (0.1–1 μm) and micronsize grains (>1 μm) with random orientations. Mechanical properties of the material were examined at room and high temperatures by compression test. It was found that the yield strength of the UFG composite material is mainly controlled by the Orowan mechanism rather than the grain boundaries. The deformation activation energy at temperature ranges of T < 300 °C and 300 °C ≤ T < 450 °C was determined to be 74 and 264 kJ mol⁻¹, respectively. This observation indicated a change in the deformation mechanism at around 300 °C. At the higher temperatures, significant deformation softening was observed due to dynamic recrystallization of non-equilibrium grain boundaries. The reinforcement nanoparticles, however, renders the high strength of the material at the elevated temperatures mainly by dislocation pinning.     

Al2O3颗粒形貌对注凝成型ZrO2/Al2O3陶瓷性能的影响

采用3种不同形貌的Al₂O₃原料对注凝成型制备ZrO₂/Al₂O₃（ZTA）陶瓷工艺中悬浮体的流变性能进行了研究。以低毒的单体N,N-二甲基丙烯酰胺（DMAA）制备了ZrO₂/Al₂O₃坯体和陶瓷。讨论了3种不同形貌的Al₂O₃原浆料的分散剂用量、球磨时间和固含量对浆料流变性的影响。Al₂O₃粉体呈扁平状有利于降低浆料的黏度,Al₂O₃粉体呈棒状对生坯强度的提高有利。制得的3种ZrO₂/Al₂O₃坯体颗粒间结合紧密,抗弯强度分别达到21.45,19.87,25.90 MPa。Al₂O₃粉体呈颗粒状有利于最终陶瓷力学性能的提高,陶瓷的抗弯强度及断裂韧性分别为680 MPa和7.49 MPa·m^1/2,453.1 MPa和6.8 MPa·m^1/2,549.4 MPa和6.34 MPa·m^1/2。     

Al2O3颗粒对Al2O3p/Al复合材料时效析出的影响

本文通过采用硬度测量,差热分析及透射电镜综合研究了Al₂O₃p/6061复合材料在时效过程中的析出变化。结果表明,在Al₂O₃p/6061时效过程中,峰时效的主要强化相是β'相,并且以160℃,8小时时效的效果为最佳。     

Al2O3基多孔隔热材料表面Al2O3/MoSi2涂层的制备及其性能

采用刷涂法在Al₂O₃基多孔隔热材料表面制备Al₂O₃/MoSi₂涂层,涂层以硅溶胶作为粘结剂,纳米Al₂O₃与Al₂O₃纤维作为耐高温组分,MoSi₂为高发射率组分。通过SEM、XRD对Al₂O₃/MoSi₂涂层微观表面结构、物相组成进行分析。研究纳米Al₂O₃与Al₂O₃纤维的质量比和MoSi₂含量对Al₂O₃/MoSi₂涂层耐温性能的影响,并对Al₂O₃/MoSi₂涂层的抗热震性能、发射率进行表征。结果表明,当纳米Al₂O₃与Al₂O₃纤维的质量比小于1∶1时,热考核后Al₂O₃/MoSi₂涂层表面无裂纹产生;当纳米Al₂O₃与Al₂O₃纤维的质量比在1∶2~1∶4之间时,Al₂O₃/MoSi₂涂层中的纤维网络较完整。MoSi₂的含量为20%时,Al₂O₃/MoSi₂涂层抗热震实验循环25次后表面保持完好,热考核后在2.5~25 μm波段的平均发射率在0.85左右,具有较高的发射率。      

Processing, microstructure and properties of C40 Mo(Si,Al)2/Al2O3 composites

The C40 Mo(Si_0.75Al_0.25)₂/Al₂O₃ composites were prepared by spark plasma sintering (SPS) of mechanically alloyed (MA) powders. The Mo(Si_0.75Al_0.25)₂/0–20 vol.% Al₂O₃ materials, showing micron and submicron composite structure, possess a hardness of 13.9–14.6 GPa but a poor toughness of 1.78–1.80 MPa m^1/2. The addition of 30 vol.% Al₂O₃ leads to the formation of the micron C40 Mo(Si_0.75Al_0.25)₂/Al₂O₃ composite with an intergranular distribution of Al₂O₃, that results in a drop of the hardness to 10.2 GPa and an improvement of the toughness to 3.67 MPa m^1/2. The transition of the cleavage facets to the intergranular fracture with the addition of Al₂O₃ is assumed as the main toughening mechanism.     

Palladium nanoparticle seeded electroless metallization of Al/Al2O3 surfaces

A simple method for the formation of palladium nanoparticles on aluminum and aluminum oxide surface is demonstrated. In the present method, the palladium nanoparticles obtained directly on the solid surface by immersing the specimen in palladium(II)acetate solution followed by reduction to metallic palladium by using sodium hypophosphite. In the investigation, as-received, boiled, electropolished and anodized aluminum was used as substrate. Additionally, the method is combined with the electroless nickel plating, which facilitates two steps metallization technique on the respective surfaces. In these cases, specimens were first immersed in palladium(II)acetate solution followed by immersion in electroless nickel plating solution, where, palladium reduced on the specimen surface providing catalytic site for the subsequent electroless nickel deposition. Using the technique, about 6 to 8.5 µm thick Ni-P metallic layer was deposited on the specimen surface.     

Growth of La2Mo2O9 films on porous Al2O3 substrates by radio frequency magnetron sputtering

Synthesis conditions of La₂Mo₂O₉ thin film by radio frequency (RF) sputtering technique on Al₂O₃ ceramic substrates are studied. It is found that the deposition temperature and oxygen partial pressure are the most important factors for obtaining pure La₂Mo₂O₉ films. Varying both parameters, Mo-rich, stoichiometric, and Mo-deficient films are obtained. With increasing the La:Mo ratio, films become denser. A crust layer is observed on top of the Mo-rich and the Mo-deficient films. The formation of the La₂Mo₂O₉ phase is discussed with respect to the sputtering mechanism.     

(Al2O3)f/Al复合材料在强界面结合下的疲劳损伤模式

在拉-拉载荷下测定了(Al₂O₃)_f/Al复合材料的疲劳寿命(S-N)曲线。通过夭折试验以及SEM疲劳断口和纵截面组织结构分析,研究了复合材料的疲劳损伤模式。研究结果表明,(Al₂O₃)_f/Al复合材料的疲劳极限为750MPa,远高于SCS-6碳化硅纤维增强钛基复合材料。该复合材料兼有钛基和树脂基纤维复合材料疲劳损伤的特点,高应力下由单个裂纹的起源和生长导致复合材料的失效;低应力下,疲劳损伤模式包括纤维劈裂、众多基体裂纹和单个基体裂纹的横向扩展。其中纤维劈裂是主控机制。其更高的疲劳极限可归因于低应力下纤维的纵向劈裂。     

Growth of Al2O3 thin film by oxidation of resistively evaporated Al on top of SnO2, and electrical properties of the heterojunction SnO2/Al2O3

Aiming for the investigation of insulating properties of aluminum oxide (Al₂O₃) layers, as well as the combination of this oxide with tin dioxide (SnO₂) for application in transparent field effect transistors, Al thin films are deposited by resistive evaporation on top of SnO₂ thin films deposited by sol–gel dip-coating process. The oxidation of Al films to Al₂O₃ are carried out by thermal annealing at 500 °C in room conditions or oxygen atmosphere. X-ray diffraction data indicate that tetragonal Al₂O₃ is indeed obtained. A simple device and electric circuit is proposed to measure the insulating properties of aluminum oxide and the transport properties of SnO₂ as well. Results indicate a fair insulation when four layers or Al₂O₃ are grown on the tin dioxide film, concomitant with thermal annealing between each layer. The current magnitude through the insulating layer is only 0.2% of the current through the semiconductor film, even though the conductivity of the SnO₂ alone is not very high (the average resistivity is 2 Ω cm), because no doping is used. The presented results are a good indication that this combination may be useful for transparent devices.     

Effect of Al2O3 particle size on vacuum breakdown behavior of Al2O3/Cu composite

In order to clarify the effect of Al₂O₃ particle size on the arc erosion behavior of the ceramic-reinforced Al₂O₃/Cu composite, Al₂O₃/Cu composites with different sizes of Al₂O₃ particles were prepared by powder metallurgy, the effect of Al₂O₃ particle size on the characteristics of arc motion was studied, and the mechanism of arc erosion of Al₂O₃/Cu composites was discussed as well. The results show that with decrease in the size of Al₂O₃ particles, the erosion area increases significantly and the erosion pits become shallower. The vacuum breakdown is preferred to appear in the area between Al₂O₃ particle and the copper matrix. Based on the experimental results and theoretical analysis, a particle partition arc model is proposed.     

CoAl2O4/Al2O3纳米复合陶瓷的结构与表征

利用溶胶-凝胶方法制备了的CoAl2O4/Al2O3纳米复合陶瓷,并用X-ray分析(XRD)、红外光谱(IR)和扫描电镜分析(SEM)对其结构进行了分析.结果表明,随Al2O3含量增多,CoAl2O4尖晶石相从CoAl2O4/Al2O3凝胶中的析晶温度升高.SEM形貌也说明,随Al2O3含量增多,CoAl2O4/Al2O3陶瓷中形成一定的层状结构.     

机械化学合成Ni2Al3/Al2O3去合金化制备Raney-Ni/Al2O3复合粉体

以NiO粉和Al粉为原料,采用机械球磨诱发化学反应制备了Ni_2Al_3/Al_2O_3复合粉体。利用X射线衍射仪(XRD)和附带能量色散谱仪(EDS)的扫描电子显微镜(SEM)对复合粉体球磨过程中的固态反应过程、表面形貌进行表征。将Ni_2Al_3/Al_2O_3复合粉体用浓度为20%的NaOH溶液腐蚀2h,可得到纳米晶结构的Ni/Al_2O_3复合粉体。利用XRD和TEM对其物相和结构进行了表征。结果表明,球磨1h后混合粉末仍为NiO粉和Al粉,球磨3h后NiO粉和Al粉在机械力的作用下反应形成Ni_2Al_3和Al_2O_3粉体,机械力诱发的NiO和Al之间的反应属于突发型反应,继续球磨10h后形成Ni_2Al_3/Al_2O_3复合粉体。Ni_2Al_3/Al_2O_3复合粉体在70℃、质量比为20%NaOH溶液中刻蚀2h,可获得Ni/Al_2O_3复合粉体。     

Al2O3-TiC/Al2O3-TiC-CaF2复合叠层陶瓷材料摩擦磨损性能

将Al₂O₃-TiC陶瓷材料与具有固体润滑特性的Al₂O₃-TiC-CaF₂陶瓷材料进行叠层, 通过真空热压烧结制备Al₂O₃-TiC/Al₂O₃-TiC-CaF₂复合叠层陶瓷材料。在环盘式摩擦磨损试验机上进行摩擦磨损实验, 研究该材料在不同载荷、 转速条件下的摩擦系数和磨损率, 分别用SEM及EDS观察材料磨损前后的微观形貌和分析其成分组成, 研究其磨损机制。结果表明: 在相同载荷条件下, Al₂O₃-TiC/Al₂O₃-TiC-CaF₂复合叠层陶瓷材料的摩擦系数和磨损率随着转速的升高而下降, 在相同转速条件下, 其摩擦系数和磨损率随着载荷的增加而下降; Al₂O₃-TiC/Al₂O₃-TiC-CaF₂复合叠层陶瓷材料的磨损机制主要是磨粒磨损和黏着磨损。     

Charge trapping characteristics of Al2O3/Al-rich Al2O3/SiO2 stacked films fabricated by radio-frequency magnetron co-sputtering

A thin-film structure comprising Al₂O₃/Al-rich Al₂O₃/SiO₂ was fabricated on Si substrate. We used radio-frequency magnetron co-sputtering with Al metal plates set on an Al₂O₃ target to fabricate the Al-rich Al₂O₃ thin film, which is used as a charge storage layer for nonvolatile Al₂O₃ memory. We investigated the charge trapping characteristics of the film. When the applied voltage between the gate and the substrate is increased, the hysteresis window of capacitance-voltage (C-V) characteristics becomes larger, which is caused by the charge trapping in the film. For a fabricated Al-O capacitor structure, we clarified experimentally that the maximum capacitance in the C-V hysteresis agrees well with the series capacitance of insulators and that the minimum capacitance agrees well with the series capacitance of the semiconductor depletion layer and stacked insulator. When the Al content in the Al-rich Al₂O₃ is increased, a large charge trap density is obtained. When the Al content in the Al-O is changed from 40 to 58%, the charge trap density increases from 0 to 18 × 10¹⁸ cm^− 3, which is 2.6 times larger than that of the trap memory using SiN as the charge storage layer. The device structure would be promising for low-cost nonvolatile memory.