Effect of Al2O3 particles on mechanical properties of directionally solidified intermetallic Ti–46Al–2W–0.5Si alloy

The effect of Al₂O₃ particles on microhardness and room-temperature compression properties of directionally solidified (DS) intermetallic Ti–46Al–2W–0.5Si (at.%) alloy was studied. The ingots with various volume fractions of Al₂O₃ particles and mean ₂–₂ interlamellar spacings were prepared by directional solidification at constant growth rates ranging from 2.78×10⁻⁶ to 1.18×10⁻⁴ ms⁻¹ in alumina moulds. The ingots with constant volume fraction of Al₂O₃ particles and various mean interlamellar spacings were prepared by directional solidification at a growth rate of 1.18×10⁻⁴ ms⁻¹ and subsequent solution annealing followed by cooling at constant rates varying between 0.078 and 1.889 K s⁻¹. The mean ₂–₂ interlamellar spacing λ for both DS and heat-treated (HT) ingots decreased with increasing cooling rate according to the relationship λ∝ ^−0.46. In DS ingots, microhardness, ultimate compression strength, yield strength and plastic deformation to fracture increased with increasing cooling rate. In HT ingots, microhardness and yield strength increased and ultimate compression strength and plastic deformation to fracture decreased with increasing cooling rate. The yield stress increased with decreasing interlamellar spacing and increasing volume fraction of Al₂O₃ particles. A linear relationship between the Vickers microhardness and yield stress was found for both DS and HT ingots. A simple model including the effect of interlamellar spacing and increasing volume fraction of Al₂O₃ particles was proposed for the prediction of the yield stress.     

Spectra and laser properties of Er, Yb:phosphate glasses

The effects of Al₂O₃, Yb₂O₃, Er₂O₃ and OH on spectral properties of P₂O₅·Na₂O·SrO·Al₂O₃·Yb₂O₃·Er₂O₃ erbium phosphate glass were studied. 5, 8, 13 mol% Al₂O₃, 4, 5, 6, 7 and 8 mol% Yb₂O₃ and 0.05, 0.2, 0.4 mol% Er₂O₃ were used. It was found Al₂O₃ improves fluorescent lifetime of Er³⁺ ions, but the integrated absorption cross-section of Er³⁺ ions decreases with the increase of Al₂O₃ concentration. Evaluating from energy transfer efficiency of Yb³⁺ to Er³⁺ and spectral parameters of Yb³⁺ and Er³⁺, lower Al₂O₃ content, 6 mol% Yb₂O₃ and 0.2–0.4 mol% Er₂O₃ are preferred for LD pumped microchip laser application. OH groups in glass greatly affect fluorescent intensity and lifetime of Er³⁺, Yb³⁺:phosphate glass. The OH absorption coefficient at 3000 cm⁻¹ should be <1 cm⁻¹ for laser applications. Pumped with a 2 W, 974 nm InGaAs laser diode, CW laser centered at 1530 nm with slope efficiency of 10.6% and maximum output of 43 mW was achieved in our 2 mm thick Er³⁺, Yb³⁺:phosphate glass at room temperature.     

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.     

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。     

Ag glasses based on Zn-phosphate

The partial substitution of Zn²⁺ for Ag⁺ in Ag₄P₂O₇ leads to the formation of a wide glassy domain of composition [Ag₄P₂O₇] _(1−y) [Zn₂P₂O₇] _(y) with 0.20y0.87. The introduction of AgI in these materials results in a new series of glasses of formula [(Ag₄P₂O₇)_(1−y) (Zn₂P₂O₇)_(y)] _(1−X) [AgI] _(x), which domain for the composition y = 0.25 corresponds to 0x 0.64. The structure as well as the thermal and electrical properties of these materials are compared with those of the [AgPO₃] _(1−X) [AgI] _(x) and [Ag₄P₂O₇] _(1−x) [AgI] _(x) glasses.     

Controllable formation of Er–Yb codoped Al2O3 films by the non-aqueous sol–gel method

1 mol%Er³⁺–10 mol%Yb³⁺ codoped Al₂O₃ thin films have been prepared on thermally oxidized SiO₂/Si(110) substrates by a dip-coating process in the non-aqueous sol–gel method from the hydrolysis of aluminum isopropoxide [Al(OC₃H₇)₃] under isopropanol environment. Addition of N,N-dimethylformamide (DMF) as a drying control chemical additive (DCCA) into the sol suppresses formation of the cracks in the Er³⁺–Yb³⁺ codoped Al₂O₃ thin films when the rare-earth ion is doped with a high doping concentration. Homogeneous, smooth and crack-free Er³⁺–Yb³⁺ codoped Al₂O₃ thin films form at the conditions by a molar ratio of 1:1 for DMF:Al(OC₃H₇)₃. A strong photoluminescence spectrum with a broadband extending from 1.400 to 1.700 µm centered at 1.533 µm is obtained for the Er³⁺–Yb³⁺ codoped Al₂O₃ thin films, which is unrelated to the addition of DMF. Controllable formation of the Er³⁺–Yb³⁺ codoped Al₂O₃ thin films may be explained by the fact that the DMF assisted the deprotonation process of Al–OH at the surfaces of gel particles, resulting in enhancement of the degree of polymerization of sols and improvement of the mechanical properties of gel thin films.     

A New Unidirectional Solidified Ceramic Eutectic with High Strength at High Temperature

New eutectic composites such as Al₂O₃/Er₃Al₅O₁₂ or Al₂O₃/GdAlO₃ have recently been fabricated by unidirectional solidification. The eutectic composite has a new microstructure, in which continuous networks of Al₂O₃ phases and oxide compounds (Er₃Al₅O₁₂ or GdAlO₃) interpenetrate without grain boundaries. The eutectic composite is thermally stable and has the following properties. In case of Al₂O₃/Er₃Al₅O₁₂ composite,

1. The flexural strength at room temperature can be maintained up to 2073 K (just below its melting point of about 2130 K),

2. The compressive flow stress at 1873 K and a strain rate of 10^-4/sec is about 8 times higher than that of sintered composites of the same composition,

3. It shows neither weight gain nor grain growth, even upon heating at 1973 K in an air atmosphere for 500 hours. In case of Al₂O₃/GdAlO₃ composite, and

4. It shows substantial plastic deformation at 1873 K with a flexural yield stress of about 700 MPa. It is found that the plastic deformation occurred by dislocation motion in each phase.     

On the structure of the NiO–Al2O3 systems, studied by diffuse-reflectance spectroscopy

Diffuse-reflectance spectra of the NiO–Al₂O₃ systems in the 350–800 nm spectral domain are analysed. Two types of Ni²⁺complexes in γ-Al₂O₃ have been found at low concentrations (<5%): [Ni²⁺6O²⁻] and [Ni²⁺4O²⁻] with octahedral (O_h) and tetrahedral (T_d) symmetries, respectively. Coexistence of these two complexes is discussed in connection with the sample preparation and their thermal treatment.     

Mechanical Properties and Thermal Stability of Oxide Eutectic Composites at High Temperatures

New unidirectionally solidified eutectic composites such as Al₂O₃/YAG and Al₂O₃/GdAlO₃(GAP) have been fabricated by unidirectional solidification. The eutectic composites have a microstructure, in which single crystal Al₂O₃ and single crystal complex oxide compounds (YAG or GdAlO₃) are continuously connected and finely entangled in three-dimensions without grain boundaries. The eutectic composites are thermally stable and have the following properties: (1) The flexural strength at room temperature can be maintained almost up to the melting point, (2) In case of Al₂O₃/YAG composite, the compressive flow stress at 1873 K and a strain rate of 10^-4sec is about 13 times higher than that of sintered composites of the same composition, (3) Al₂O₃/YAG composite shows neither weight gain nor grain growth, even upon heating at 1973 K in an air atmosphere for 1000 hours, and (4) The Al₂O₃/GdAIO₃ eutectic composite shows substantial plastic deformation at 1873 K with a flexural yield stress of about 690 MPa, where the plastic deformation occurred by dislocation motion in each phase. Consequently, these composites can be considered for several useful applications such as new aero gas turbines and power generation systems with non-cooled turbine blades at above 1773 K.     

高功率激光照明用Al2O3-YAG:Ce复相陶瓷荧光体的组分设计与性能优化

结合蓝色激光二极管和黄色荧光转换器制备的固态激光照明引起了人们极大的关注, 但荧光转换材料的热猝灭效应显著影响了高功率激光照明的实现。通过组分设计和性能优化可以提高荧光转换器的热导率和发光均匀性。本工作采用固相反应烧结技术制备了一系列不同Al₂O₃含量的Al₂O₃-YAG:Ce复相陶瓷荧光体, 研究了Al₂O₃含量对Al₂O₃-YAG:Ce陶瓷荧光体微观结构、相组成、光学性能和热学性能的影响。Al₂O₃-YAG:Ce陶瓷荧光体在800 nm处的总透过率随着Al₂O₃含量的增加(0→90%)而下降(82.6%→23.6%)。Al₂O₃-YAG:Ce陶瓷荧光体的激发和发射强度随Al₂O₃含量的增加先增大后减小。当Al₂O₃/Al₂O₃-YAG:Ce的质量比为70%时, 陶瓷荧光体在室温下的热导率高达25.7 W·m^-1·K^-1, 且表现出最高的发射强度。当采用功率密度为20 W·mm^-2的蓝光二极管泵浦 70% Al₂O₃-YAG:Ce复相陶瓷荧光体时, 可获得3724 lm的高光通量和239.4 lm·W^-1的高流明效率。此外, 当功率密度从1 W·mm^-2增大到20 W·mm^-2时, 流明效率仅下降10.5%, 光通量持续增加且未出现发光饱和。上述结果显示, Al₂O₃-YAG:Ce复相陶瓷荧光体具有良好的发光效率和热稳定性, 将在高功率激光照明中具有广阔的应用前景。     

Elevated temperature creep behavior of three rapidly solidified Al-Fe-Si materials containing Cr, Mn, or Mo

Research on the high temperature creep behavior of three rapidly solidified Al-Fe-X-Si (where X = Cr, Mn or Mo) dispersion strengthened materials with three different alloying compositions has been conducted. Firstly, microstructural examinations have been carried out on the as-received, thermally treated and tested samples. The microstructure consists of a fine Al matrix embedding small round-shaped Al₁₂(Fe,X)₃Si and Al₁₃(Fe,X)₄ dispersoids. Grain sizes ranging from 0.85 to 1.45 μm and dispersoid sizes ranging from 45 to 54 nm were observed. Secondly, tensile tests were performed at high temperature from 573 to 823 K at strain rates ranging from 2.5×10⁻⁶ to 10⁻²s⁻¹. The experimental data exhibited high apparent stress exponent, n_ap, and high activation energy, Q_ap. The rnicrostructure remained stable and fine after testing. The results are analyzed by means of various models used in the literature.     

Al2O3 formation on Si by catalytic chemical vapor deposition

Catalytic chemical vapor deposition (Cat-CVD) has been developed to deposit alumina (Al₂O₃) thin films on silicon (Si) crystals using N₂ bubbled tri-methyl aluminum [Al(CH₃)₃, TMA] and molecular oxygen (O₂) as source species and tungsten wires as a catalyzer. The catalyzer dissociated TMA at approximately 600 °C. The maximum deposition rate was 18 nm min⁻¹ at a catalyzer temperature of 1000 °C and substrate temperature of 800 °C. Metal oxide semiconductor (MOS) diodes were fabricated using gates composed of 32.5-nm-thick alumina film deposited at a substrate temperature of 400 °C. The capacitance measurements resulted in a relative dielectric constant of 7.4, fixed charge density of 1.74×10¹² cm⁻², small hysteresis voltage of 0.12 V, and very few interface trapping charges. The leakage current was 5.01×10⁻⁷ A cm⁻² at a gate bias of 1 V.     

ZnO·2.56Al2O3透明陶瓷凝胶注模成型与烧结制备

锌铝尖晶石透明陶瓷是典型的结构功能一体化材料, 具有优异的光学、热学以及介电性能。本研究以ZnAl₂O₄和Al₂O₃为原料, 通过凝胶注模成型制备ZnAl₂O₄-Al₂O₃复相陶瓷初坯。实验探究了分散剂含量、pH以及固相量对ZnAl₂O₄-Al₂O₃混合料浆流变学特性的影响, 制得固相量为50vol%的低黏度稳定料浆。浇注成型后的坯体通过无压烧结和热等静压反应烧结制备透明陶瓷。最终获得的ZnO·2.56Al₂O₃透明陶瓷样品在厚度为1.8 mm下可见光波段透过率达到70%, 红外波段透过率达到80%以上, 维氏硬度为(11.34±0.17) GPa, 杨氏模量为285 GPa。     

Ionic Conductivity and Mechanical Properties of Post-HIPed Cubic Zirconia/Alumina Composites

8 mol.% yttria-doped cubic zirconia (8Y-CSZ)/AI₂O₃ composites containing 0-30 vol.% Al₂O₃ particles were fabricated by sintering, followed by hot isostatic pressing (post-HIPing). All composites were densified to at least 99·5% of the theoretical density by post-HIPing. The bending strength of composites sintered at 1500°C in air was independent of A1₂O₃ content, but a significant improvement in the bending strength was achieved by the post-HIPing technique. The bending strength and the fracture toughness of the HIPed composites increased with increasing A1₂O₃ content. Ionic conductivity of the composites was evaluated and the total, lattice, and grain boundary conductivities slightly decreased with increasing A1₂O₃ content. The HIPed composites containing up to 20 vol.% A1₂0₃ appear to be suitable candidate materials as electrolyte for solid oxygen fuel cell.     

Preparation and characterization of LiAl0.23Mn1.77O4 for supercapacitor electrodes

LiAl_0.23Mn_1.77O₄ was synthesized by high temperature solid-state reaction. The structure and morphology of LiAl_0.23Mn_1.77O₄ were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). The supercapacitive performances of LiAl_0.23Mn_1.77O₄ materials were studied using galvanostatic charge/discharge measurements, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods in 2 mol L⁻¹ (NH₄)₂SO₄ solution. The results show that the LiAl_0.23Mn_1.77O₄ electrode exhibits typical supercapacitive characteristics in aqueous (NH₄)₂SO₄ electrolyte. The specific capacitance is up to 185 F g⁻¹ at current density of 2 mA cm⁻². The ohmic resistance (R_sol) is only 0.22 Ω. Besides, the electrodes showed a stable cycle life in the potential range of 0–1.0 V and retained 93% of initial specific capacitance over 100 cycles.     

Microstructures, densification and mechanical properties of TiC–Al2O3–Al composite by field-activated combustion synthesis

Dense TiC–Al₂O₃–Al composite was prepared with Al, C and TiO₂ powders by means of electric field-activated combustion synthesis and infiltration of the molten metal (here Al) into the synthesized TiC–Al₂O₃ ceramic. An external electric field can effectively improve the adiabatic combustion temperature of the reactive system and overcome the thermodynamic limitation of reaction with x < 10 mol. Thereby, it can induce a self-sustaining combustion synthesis process. During the formation of Al₂O₃–TiC–Al composite, Al is molten first, and reacted with TiO₂ to form Al₂O₃, followed by the formation of TiC through the reaction between the displaced Ti and C. Highly dense TiC–Al₂O₃–Al with relative density of up to 92.5% was directly fabricated with the application of a 14 mol excess Al content and a 25 V cm⁻¹ field strength, in which TiC and Al₂O₃ particles possess fine-structured sizes of 0.2–1.0 μm, with uniform distribution in metal Al. The hardness, bending strength and fracture toughness of the synthesized TiC–Al₂O₃–Al composite are 56.5 GPa, 531 MPa and 10.96 MPa m^1/2, respectively.     

Bi2O3助熔剂对CaO-B2O3-SiO2/Al2O3玻璃陶瓷复合材料性能的影响

以CaO-B₂O₃-SiO₂(CBS)玻璃粉体和Al₂O₃陶瓷粉体为原料,通过在CBS与Al₂O₃的质量比固定为50:50的玻璃-陶瓷复合材料中添加适量的Bi₂O₃作为烧结助熔剂,探讨了Bi₂O₃助熔剂对CBS/Al₂O₃复合材料的烧结性能、介电性能、抗弯强度和热膨胀系数的影响规律.研究表明:Bi₂O₃助熔剂能通过降低CBS玻璃的转变温度和黏度促进CBS/Al₂O₃复合材料的致密化进程,于880 ℃下烧结即能获得结构较致密、气孔较少的CBS/Al₂O₃复合材料.然而,过量添加Bi₂O₃将使玻璃的黏度过低,从而恶化CBS/Al₂O₃复合材料的烧结性能、介电性能及抗弯强度.当Bi₂O₃的添加量为CBS/Al₂O₃复合材料的1.5wt%时,于880 ℃下烧结即能获得最为致密的CBS/Al₂O₃复合材料,密度为2.82 g·cm^-3,这一材料具有良好的介电性能(介电常数为7.21,介电损耗为1.06×10^-3),抗弯强度为190.34 MPa,0~300 ℃的热膨胀系数为3.52×10^-6 K^-1.     

Effects of TiO/Al ratio on microstructures and mechanical properties of TiAl base composites

Effects of TiO₂/Al ratio on the microstructures and mechanical properties of in situ Al₂O₃/TiAl based composites were investigated. The results indicate that the as-sintered products consist of grains of nearly lamellar ?₂ + ? structure with a dispersion of randomly oriented Al₂O₃ particles. A 43.9Ti-38.6Al-17.5TiO₂-nNb₂O₅ system was compared to 57.46Ti-36.78Al-5.76TiO₂-nNb₂O₅ system. The lamellar spacing of the products increases and the ?₂ phase volume decreases with decreasing TiO₂/Al ratio. For each system, as the volume of ?₂ phase increases, the average lamellar spacing decreases. Strength increases with an increasing TiO₂/Al ratio due to the amount of ?₂ phase. Al₂O₃ phase increases with increasing TiO₂/Al ratio. Toughness increases with decreasing TiO₂/Al ratio. When the Nb₂O₅ content is smaller than 6 wt.%, the lamellar spacing plays an important role in toughness than the Al₂O₃ content. When the Nb₂O₅ content is larger than 6 wt.%, the Al₂O₃ content exhibits significantly increases the values of toughness than lamellar spacing.     

低温制备不锈钢表面含铜磷酸铝涂层及抗菌性能研究

利用磷酸二氢铝的固化反应在316不锈钢表面制备了不同含量Cu²⁺的磷酸铝涂层(Cu: Al=0.025、0.05、0.1)。差示扫描量热分析及X射线衍射表明涂层材料可在≤250℃下固化, 主要固化产物为AlH₂P₃O₁₀∙2H₂O、AlPO₄和Al₈H₁₂(P₂O₇)₉。Cu²⁺加入后产生了含铜的新相Cu₂P₂O₇。与大肠杆菌共培养12 h后各含Cu²⁺涂层表现出抗菌性, 且抗菌能力与Cu²⁺含量正相关; 接触24 h后, 所有含Cu²⁺涂层表面均无活菌检出。菌悬液中加入EDTA有效抑制了涂层抗菌活性, 表明涂层抗菌性能来自表面溶出的Cu²⁺。拉伸试验表明涂层结合强度在14.5~18.1 MPa范围。与无涂层的不锈钢相比, 涂覆涂层后样品的腐蚀电流密度下降了2个数量级。     

Multi-composition oxidation resistant coating for SiC-coated carbon/carbon composites at high temperature

This work proposes a multi-composition oxidation resistant coating for SiC-coated carbon/carbon (C/C) composites by slurry method using the mixture of Y₂O₃, ZrO₂, Al₂O₃, Si and C. XRD analysis shows that the phases of the composite coating are composed of SiC, Al₂O₃, Y₂O₃, ZrO₂, Al₄SiC₄ and Y₃Al₂(AlO₄)₃. SEM analysis of the cross section of the coating displays the microstructure with 500 μm thickness which filled the porous SiC. Oxidation test shows that, after 19 h oxidation in air at 1873 K, the weight loss of the coated SiC-C/C is only 1.76%. The oxidation of the coated C/C composites was primarily due to the reaction of C/C matrix and oxygen diffusing through the penetrable cracks and bubble holes in the coating.