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1.
TiB 2–Al 2O 3 composites with Ni–Mo as sintering aid have been fabricated by a hot-press technique at a lower temperature of 1530 °C for 1 h, and the mechanical properties and microstructure were investigated. The microstructure consists of dispersed Al 2O 3 particles in a fine-grained TiB 2 matrix. The addition of Al 2O 3 increases the fracture toughness up to 6.02 MPa m 1/2 at an amount of 40 vol.% Al 2O 3 and the flexural strength up to 913.86 MPa at an amount of 10 vol.% Al 2O 3. The improved flexural strength of the composites is a result of higher density than that of monolithic TiB 2. The increase of fracture toughness is a result of crack bridging by the metal grains on the boundaries, and crack deflection by weak grain boundaries due to the bad wetting characters between Ni–Mo and Al 2O 3. 相似文献
2.
2r0 2 and its modified versions containing MgO and Y 20 3 were selected as particulate reinforcement in order to achieve better mechanical properties in fused mullite. Particulate composites containing up to 25 vol% Zr0 2 and its modifications were pressed to 65% relative density at 350 MPa followed by sintering at 1650°C and 1700°C for one hour. Studies were conducted on fracture toughness, transverse rupture strength, dielectric constant, microstructure, fractography and thermal shock resistance. Composites sintered at 1700°C were found superior in properties than those sintered at 1650°C. 相似文献
3.
The C40 Mo(Si 0.75Al 0.25) 2/Al 2O 3 composites were prepared by spark plasma sintering (SPS) of mechanically alloyed (MA) powders. The Mo(Si 0.75Al 0.25) 2/0–20 vol.% Al 2O 3 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.% Al 2O 3 leads to the formation of the micron C40 Mo(Si 0.75Al 0.25) 2/Al 2O 3 composite with an intergranular distribution of Al 2O 3, 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 Al 2O 3 is assumed as the main toughening mechanism. 相似文献
4.
Grain growth in the two-phase (liquid + solid) region of Ni 3Al reinforced with 0.8 vol.% Al 2O 3 participates synthesized by a spray atomization and co-injection technique was investigated. The grain growth of the as-sprayed and hot isostatically pressed (HIPed) materials in the two-phase region was found to be consistent with cube law kinetics, i.e., grain growth exponent was approximately 3. The activation energy for grain growth for the as-sprayed material was determined to be 308 ± 19 kJ mol −1 while that of the HIPed material was calculated to be 327 ± 23 kJ mol −1. The activation energy for grain growth was not a function of the amount of liquid phase or the composition of the liquid. Furthermore, the activation energy for grain growth was higher than that for diffusion through the liquid phase, suggesting that the mechanism for grain growth of the as-sprayed and HIPed Ni 3Al composite in the two-phase region was controlled by an interface reaction. The role of the second-phase Al 2O 3 particles on grain growth for the as-sprayed and HIPed Ni 3Al materials was not significant. 相似文献
5.
High performance nanocomposites were prepared by incorporating 0–12 vol.% nano-sized (39 nm) Al 2O 3 particles into PEEK matrix using compression molding. The microhardness and dynamic mechanical properties of the nanocomposites increase with increasing Al 2O 3 content. The wear resistance of the nanocomposites evaluated at a sliding speed of 1.0 m/s and nominal pressure from 0.5 MPa to 1.25 MPa under dry sliding conditions was improved more than threefold at 0.8 vol.% Al 2O 3 content. However, the wear resistance of the nanocomposites containing above 1.67 vol.% Al 2O 3 was deteriorated, despite their higher hardness and stiffness as compared to that of nanocomposites containing lower Al 2O 3 content. The surface roughness of the wear track formed over the countersurface increases with increasing Al 2O 3 content. The coefficient of friction of nanocomposites was higher than that of pure PEEK. SEM and optical microscopy have shown that wear of pure PEEK occurs by the mechanism of adhesion mainly, whereas of nanocomposites by microploughing and abrasion. Energy dispersive spectrometry (EDS) shows that Fe and alloying elements of countersurface transfer to the wear debris at higher Al 2O 3 content. 相似文献
6.
Effects of TiO 2/Al ratio on the microstructures and mechanical properties of in situ Al 2O 3/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 Al 2O 3 particles. A 43.9Ti-38.6Al-17.5TiO 2-nNb 2O 5 system was compared to 57.46Ti-36.78Al-5.76TiO 2-nNb 2O 5 system. The lamellar spacing of the products increases and the ? 2 phase volume decreases with decreasing TiO 2/Al ratio. For each system, as the volume of ? 2 phase increases, the average lamellar spacing decreases. Strength increases with an increasing TiO 2/Al ratio due to the amount of ? 2 phase. Al 2O 3 phase increases with increasing TiO 2/Al ratio. Toughness increases with decreasing TiO 2/Al ratio. When the Nb 2O 5 content is smaller than 6 wt.%, the lamellar spacing plays an important role in toughness than the Al 2O 3 content. When the Nb 2O 5 content is larger than 6 wt.%, the Al 2O 3 content exhibits significantly increases the values of toughness than lamellar spacing. 相似文献
7.
用石墨埋烧方法制备Fe/Al 2O 3复合材料,对其力学性能和微观结构进行了分析。结果表明:Fe/Al 2O 3复合材料的弯曲强度与断裂韧性均随Al 2O 3含量的升高先升高后降低,当Al 2O 3含量(质量分数)为70%时,其弯曲强度与断裂韧性分别达到602.49 MPa和9.33 MPa·m 1/2,其硬度随Al 2O 3含量先降低后升高。在烧结过程中在Fe颗粒周围形成一种成分为FeO与FeAl 2O 4的壳体,在壳体与Fe颗粒之间存在微裂纹缺陷。壳体的形成和壳体与金属颗粒间的微裂纹钝化了外部应力,从而提高了复合材料的韧性。 相似文献
8.
Samarium-doped ceria (SDC) thin films were prepared from Sm(DPM) 3 (DPM = 2,2,6,6-tetramethyl-3,5-heptanedionato) and Ce(DPM) 4 using the aerosol-assisted metal–organic chemical vapor deposition method. -Al 2O 3 and NiO-YSZ (YSZ = Y 2O 3-stabilized ZrO 2) disks were chosen as substrates in order to investigate the difference in the growth process on the two substrates. Single cubic structure could be obtained on either -Al 2O 3 or NiO-YSZ substrates at deposition temperatures above 450 °C; the similar structure between YSZ and SDC results in matching growth compared with the deposition on -Al 2O 3 substrate. A typical columnar structure could be obtained at 650 °C on -Al 2O 3 substrate and a more uniform surface was produced on NiO-YSZ substrate at 500 °C. The composition of SDC film deposited at 450 °C is close to that of precursor solution (Sm : Ce = 1 : 4), higher or lower deposition temperature will both lead to sharp deviation from this elemental ratio. The different thermal properties of Sm(DPM) 3 and Ce(DPM) 4 may be the key reason for the variation in composition with the increase of deposition temperature. 相似文献
9.
为了制备低膨胀、高强、轻质复合材料,采用模压法制备了ZrW_(2)O_(8)-Cf/E51复合材料,并研究了超声时间对其微观组织、热膨胀行为和极限抗拉强度的影响。结果表明:在制备过程中颗粒团聚后容易受到纤维单丝阻挡并在纤维束表面聚集。在20 min之内,延长超声时间会减少ZrW_(2)O_(8)颗粒团聚。随着颗粒团聚的减少,复合材料断口会由平面状、无纤维拔出变为台阶状、有纤维拔出。在碳纤维和ZrW_(2)O_(8)颗粒的综合作用下,ZrW_(2)O_(8)-Cf/E51复合材料在热膨胀过程中膨胀量dL/L0会出现增大、减小和缓慢上升三个阶段,平均热膨胀系数也会出现相应的三个阶段。超声时间从5 min延长到20 min,ZrW_(2)O_(8)-Cf/E51复合材料的平均热膨胀系数降低了约130%,极限抗拉强度提高了约8%。 相似文献
10.
An effective method is developed for low temperature metal oxide deposition through thermal decomposition of metal diketonates in supercritical carbon dioxide (scCO 2) solvent. The rates of Al(acac) 3 (Aluminum acetyl acetonate) and Ga(acac) 3 (Gallium acetyl acetonate) thermal decomposition in scCO 2 to form conformal Al 2O 3 and Ga 2O 3 thin films on planar surfaces were investigated. The thermal decomposition reaction of Al(acac) 3 and Ga(acac) 3 was found to be initialized at 150 °C and 160 °C respectively in scCO 2 solvent, compared to 250 °C and 360 °C in analogous vacuum-based processes. By measuring the temperature dependence of the growth rates of metal oxide thin films, the apparent activation energy for the thermal decomposition of Al(acac) 3 in scCO 2 is found to be 68 ± 6 kJ/mol, in comparison with 80–100 kJ/mol observed for the corresponding vacuum-based thermal decomposition reaction. The enhanced thermal decomposition rate in scCO 2 is ascribed to the high density solvent which effectively reduces the energy of the polar transition states in the reaction pathway. Preliminary results of thin film deposition of other metal oxides including ZrO x, FeO x, Co 2O 3, Cr 2O 3, HfO x from thermal decomposition of metal diketonates or fluorinated diketonates in scCO 2 are also presented. 相似文献
11.
Calcium oxide and calcium hafnium oxide thin films were grown by atomic layer deposition on borosilicate glass and silicon substrates in the temperature range of 205–300 °C. The calcium oxide films were grown from novel calcium cyclopentadienyl precursor and water. Calcium oxide films possessed refractive index 1.75–1.80. Calcium oxide films grown without Al 2O 3 capping layer occurred hygroscopic and converted to Ca(OH) 2 after exposure to air. As-deposited CaO films were (200)-oriented. CaO covered with Al 2O 3 capping layers contained relatively low amounts of hydrogen and re-oriented into (111) direction upon annealing at 900 °C. In order to examine the application of CaO in high-permittivity dielectric layers, mixtures of Ca and Hf oxides were grown by alternate CaO and HfO 2 growth cycles at 230 and 300 °C. HfCl 4 was used as a hafnium precursor. When grown at 230 °C, the films were amorphous with equal amounts of Ca and Hf constituents (15 at.%). These films crystallized upon annealing at 750 °C, showing X-ray diffraction peaks characteristic of hafnium-rich phases such as Ca 2Hf 7O 16 or Ca 6Hf 19O 44. At 300 °C, the relative Ca content remained below 8 at.%. The crystallized phase well matched with rhombohedral Ca 2Hf 7O 16. The dielectric films grown on Si(100) substrates possessed effective permittivity values in the range of 12.8–14.2. 相似文献
12.
以CaO-B 2O 3-SiO 2(CBS)玻璃粉体和Al 2O 3陶瓷粉体为原料,通过在CBS与Al 2O 3的质量比固定为50:50的玻璃-陶瓷复合材料中添加适量的Bi 2O 3作为烧结助熔剂,探讨了Bi 2O 3助熔剂对CBS/Al 2O 3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:Bi 2O 3助熔剂能通过降低CBS玻璃的转变温度和黏度促进CBS/Al 2O 3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/Al 2O 3复合材料.然而,过量添加Bi 2O 3将使玻璃的黏度过低,从而恶化CBS/Al 2O 3复合材料的烧结性能、介电性能及抗弯强度.当Bi 2O 3的添加量为CBS/Al 2O 3复合材料的1.5wt%时,于880 ℃下烧结即能获得最为致密的CBS/Al 2O 3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. 相似文献
13.
This paper describes an experimental study of the compressive failure of T800/924C carbon-fibre/efoxy composite laminates. Undirectional laminates loaded parallel to the fibres have compressive strengths that are 70% of the tensile strength and fail by fibre-microbuckling. During microbuckling the fibre debonds from the matrix, and the fibres break in bending. Multidirectional [(±45/0 2) 3] sm laminates were also tested in compression, and the critical failure mechanism observed was microbuckling of the 0° plies. The failure strain was almost the same as for the undirectional laminate, The failure strain was almost the same as for the unidirectional laminate, which indicated that the ±45° plies have no significant influence on the failure strength of the 0° plies. 相似文献
14.
Metal-organic chemical vapour deposition (MOCVD) of various phases in PrO x system has been studied in relation with deposition temperature (450–750 °C) and oxygen partial pressure (0.027–100 Pa or 0.2–750 mTorr). Depositions were carried out by pulsed liquid injection MOCVD using Pr(thd) 3 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) precursor dissolved in toluene or monoglyme. By varying deposition temperature and oxygen partial pressure amorphous films or various crystalline PrO x phases (Pr 2O 3, Pr 7O 12, Pr 6O 11) and their mixtures can be grown. The pure crystalline Pr 2O 3 phase grows only in a narrow range of partial oxygen pressure and temperature, while high oxygen pressure (40–100 Pa) always leads to the most stable Pr 6O 11 phase. The influence of annealing under vacuum at 750 °C on film phase composition was also studied. Near 90% step coverage conformity was achieved for PrO x films on structured silicon substrates with aspect ratio 1:10. In air degradation of Pr 2O 3 films with transformation to Pr(OH) 3 was observed in contrast to Pr 6O 11 films. 相似文献
15.
Wear behavior of Al/Al 2O 3/C hybrid metal matrix composites fabricated by squeeze casting method was characterized. The effects of volume fraction of carbon fiber on wear behavior of hybrid composites was investigated. Wear behavior of Al/Al 2O 3/C composites was characterized by the dry spindle wear test under various sliding speeds. The wear resistance of Al/Al2O3/C composites was remarkably improved over Al/Al2O3 composites by adding carbon fibers to Al/Al2O3/C composites. Specifically, at the intermediate sliding speed the wear resistance of Al/Al2O3/C composites containing 8 vol.% carbon fiber was found to be better than that of the rest of the carbon hybrid composites. From fractographic studies, damaged sections in wear surfaces of hybrid composites at intermediate sliding speed were not observed due to the formation of solid lubrication film. The solid lubrication film which was formed as a result of adding carbon fibers improved the wear resistance of carbon hybrid composites because this film reduced the high friction force between MMCs and counter material. 相似文献
16.
The effect of Al 2O 3 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 Al 2O 3 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 Al 2O 3 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 Al 2O 3 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 Al 2O 3 particles was proposed for the prediction of the yield stress. 相似文献
17.
In general, it is very difficult to obtain obviously reinforced effect in discontinuously reinforced aluminum matrix composites at the temperature above 400 °C. In the present study, we report an effective method to improve the high-temperature tensile strength of Al 18B 4O 33w/Al composite by change of interfacial state. The pure aluminum matrix composites reinforced by Al 18B 4O 33w with different ZnAl 2O 4 coating contents were fabricated by squeeze casting. The results indicate that ZnAl 2O 4 coating of the whiskers can effectively improve the high-temperature tensile strength of Al 18B 4O 33w/Al composite, although the tensile strength of the composite decreases with increasing the tensile temperature. On the basis of fractograph analysis, the fracture mechanism of the composites at elevated temperatures was investigated. 相似文献
18.
A1 2O 3 and its mixture with 3 wt% Ti0 2 powders were prepared by fusion and crushing methods. Al 2O 3 + 13 wt% TiO 2 and A1 2O 3 + 40 wt% TiO 2 powders were mixtures of fused AI 2O 3 + 3 wt% TiO 2 and 10 wt% and 37 wt% of TiO 2respectively. Chemical analysis of the powders showed that: approximately 1 wt% of impurities were present in each powder. True and tap densities were measured and are discussed for all powders. Powder size study showed narrow range of distribution of particle size in each powder. SEM study showed that the particles were in round and other irregular shapes in all the powders. A1 2O 3 was found to be in alpha phase and TiO 2 in rutile phase. All the powders were coated by plasma spraying at 16 kW. The density of the coatings were measured and are discussed. In the coatings, A1 2O 3 was in both alpha and gamma phases. In A1 2O 3 + 13 wt% TiO 2 and A1 2O 3 + 40 wt% TiO 2 coatings, the oxygen reduction from TiO 2 was observed. 相似文献
19.
Co 3O 4 nanoparticles and cobalt (fcc-Co) powders were successfully synthesized by solvothermal process from a single precursor. The reaction of Co(Ac) 2 with sodium dodecylbenzenesulfonate (SDBS) shows evident-dependent temperature effect. At 180 °C, Co(Ac) 2 reacts with SDBS to produce precursor CoCO 3 plate structures, which are assembled by small nanoparticles. At the temperature of 250 °C, the precursor CoCO 3 can be gradually decomposed to form Co 3O 4 nanoparticles with diameter of ca. 70 nm. While, at 250 °C, the reaction of Co(Ac) 2 with SDBS also produce precursor CoCO 3 nanoparticles/plates, but the CoCO 3 nanoparticles/plates would only decompose to give metal Co. In this process, SDBS acts as not only a surfactant but also a reagent. Magnetic measurements reveal that the as-prepared Co 3O 4 nanoparticles exhibit weak ferromagnetic properties and Co powders show ferromagnetic properties. In addition, a possible formation mechanism was elaborately discussed. 相似文献
20.
用有机先驱体浸渍裂解(PIP)法制备SiC f/BN/SiC复合材料,研究了微米Al 2O 3粉体对其弯曲强度、高温介电和高温吸波性能的影响。结果表明,随着Al 2O 3的含量从5%提高到20%,SiC f/BN/SiC的弯曲强度呈现出先升高后降低的趋势,最大值达到295 MPa;随着温度的升高复合材料复介电常数的实部和虚部均逐渐增大,加入Al 2O 3填料能降低高温复介电常数及其随温度增大的幅度。无填料复合材料的室温和高温吸波性能均较差,而添加20% Al 2O 3的复合材料在8.2~12.4 GHz频段的室温反射损耗均低于-8 dB,且适用厚度为3.0~3.5 mm,700℃时厚度为3.0 mm的反射损耗为-5~-8 dB,在实际工程应用中具有较强的可设计性。 相似文献
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