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1.
High-energy milling was used for production of Cu–Al2O3 composites. The inert gas-atomized prealloyed copper powder containing 2 wt.%Al and the mixture of the different sized electrolytic copper powders with 4 wt.% commercial Al2O3 powders served as starting materials. Milling of prealloyed copper powders promotes formation of nano-sized Al2O3 particles by internal oxidation with oxygen from air. Hot-pressed compacts of composites obtained from 5 and 20 h milled powders were additionally subjected to the high-temperature exposure in argon at 800 °C for 1 and 5 h. Characterization of processed material was performed by optical and scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), microhardness, as well as density and electrical conductivity measurements. Due to nano-sized Al2O3 particles microhardness and thermal stability of composite processed from milled prealloyed powders are higher than corresponding properties of composites processed from the milled powder mixtures. The results were discussed in terms of the effects of different size of starting copper powders and Al2O3 particles on the structure, strengthening of copper matrix, thermal stability and electrical conductivity of Cu–Al2O3 composites. 相似文献
2.
The effect of different solution temperatures has been investigated on the microstructure and tensile properties of in situ Al–Mg2Si composite specimens were subjected to solutionizing at different temperatures of 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, 550 °C and 580 °C for holding time of 4 h followed by quenching. The microstructural studies of the polished and etched samples by scanning electron microscopy (SEM) in the solution condition indicated that the increase in the temperature changes the morphology of both the primary and secondary Mg2Si phases. Solutionizing led to the dissolution of the Mg2Si particles and changed their morphology. Tensile test results indicated that ultimate tensile strength (UTS) gradually decreased upon solutionizing from 300 to 550 °C while further increase in the temperature followed by a sharp decrease in UTS up to 580 °C solutionizing temperature. It was found that the elongation has become three times greater in comparison to the as-cast state. Elongation results showed an increase up to 500 °C and then reduced temperatures of 550 and 580 °C. Fractographic analysis revealed a cellular nature for the fracture surface. On the cellular fracture surface, the features of both brittle and ductile fracture were present simultaneously. As a result of solution treatment the potential sites for stress concentration and crack initiation areas were reduced due to softening of the sharp corners and break up of eutectic network respectively, while increase in the number of fine dimples rendered the nature of fracture to ductile and also increased elongation. 相似文献
3.
In this paper, electro-codeposition based on electrophoretic deposition and electrolytic deposition was developed to prepare Al2O3-Y2O3 composite thin film coatings on a γ-TiAl based alloy. Scanning electron microscope observations showed that the Al2O3-Y2O3 composite coatings were very compact and consisted of uniform nano-particles after microwave sintering. Cyclic oxidation at 900 °C indicated that the Al2O3-Y2O3 composite thin film coatings improved the oxidation and scale spallation resistance of the γ-TiAl alloy significantly. The superior oxidation and spallation resistance of the coatings were attributed to the suppression of outward diffusion of Ti and Al and inward diffusion of O, the promoted selective oxidation of Al in the γ-TiAl alloy, and the improved adhesion of oxide scale induced by the Al2O3-Y2O3 composite thin film coatings. 相似文献
4.
《Materials Letters》2004,58(3-4):432-436
In this work, CeO2 is investigated as an additive for in situ preparation of TiC/Al–Si composite using exothermal dispersion (XD)+casting technology. Experimental results show that CeO2 at high temperature exhibits the same function as Ce, which is a kind of good modificator. When 0.5 wt.% CeO2 additive is added, the microstructure of eutectic silicon is significantly changed (the size is greatly reduced). Meanwhile, the amount of TiC particles is increased and the size is reduced. Compared with the composite without added CeO2, the hardness value (HB) value, tensile strength and tensile elongation are greatly increased. However, under dry sliding friction test, weight loss of the composite is not significantly changed. 相似文献
5.
AbstractAn in situ titanium trialuminide (Al3Ti)-particle-reinforced magnesium matrix composite has been successfully fabricated by the powder metallurgy of a Mg–Al–Ti system. The reaction processes and formation mechanism for synthesizing the composite were studied by differential scanning calorimetry (DSC), x-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). Al3Ti particles are found to be synthesized in situ in the Mg alloy matrix. During the reaction sintering of the Mg–Al–Ti system, Al3Ti particles are formed through the reaction of liquid Al with as-dissolved Ti around the Ti particles. The formed intermetallic particles accumulate at the original sites of the Ti particles. As sintering time increases, the accumulated intermetallic particles disperse and reach a relatively homogeneous distribution in the matrix. It is found that the reaction process of the Mg–Al–Ti system is almost the same as that of the Al–Ti system. Mg also acts as a catalytic agent and a diluent in the reactions and shifts the reactions of Al and Ti to lower temperatures. An additional amount of Al is required for eliminating residual Ti and solid-solution strengthening of the Mg matrix. 相似文献
6.
Ni–Al2O3 composite coatings were produced by the sediment electro-codeposition (SECD) technique at various particle loadings and current densities. The submicron Al2O3 particles were found to distribute uniformly in the coating, and 12–18 vol.% particles can be incorporated in the coating depending on deposition current density and particle loading in the plating bath. Electrochemical corrosion testing was conducted in 0.9 wt.% NaCl solution. The results show that the incorporation of Al2O3 particles in the coating did not affect the general corrosion behaviour of the Ni coating. However, at higher anodic potentials approaching the breakdown potential and with prolonged polarization, the composite coatings showed deteriorated corrosion resistance in terms of increased anodic current density, reduced pitting potential and quicker breakdown of the passive film. The detrimental effects of Al2O3 particle incorporation could be explained by the existence of numerous boundaries between the particles and the matrix, which would serve as active sites for anodic dissolution and micro-pit formation. 相似文献
7.
The influence of SrO (0·0–5·0 wt%) on partial substitution of alpha alumina (corundum) in ceramic composition (95 Al2O3–5B2O3) have been studied by co-precipitated process and their phase composition, microstructure, microchemistry and microwave dielectric
properties were studied. Phase composition was revealed by XRD, while microstructure and microchemistry were investigated
by electron-probe microanalysis (EPMA). The dielectric properties by means of dielectric constant (ε
r
), quality factor (Q × f) and temperature coefficient of resonant frequency (τ
f
) were measured in the microwave frequency region using a network analyser by the resonance method. The addition of B2O3 and SrO significantly reduced the sintering temperature of alumina ceramic bodies to 1600 °C with optimum density (∼ 4g/cm3) as compared with pure alumina powders recycled from Al dross (3·55g/cm3 sintered at 1700 °C). 相似文献
8.
Ionic ferrofluids based on γ-Fe2O3/Ni2O3 composite nanoparticles are a polydispersed system prepared by the Massart method. The magnetization and optical relaxation behaviors of these ferrofluids show that, in addition to the ring-free micelle aggregates, there are also chainlike aggregates in the ferrofluids. The chainlike aggregation is attributed to so-called “depletion force” in the polydispersed ferrofluids because magnetic interaction between the ferrofluid particles is so weak that these particles cannot form the aggregates just by the magnetic interaction. For the γ-Fe2O3/Ni2O3 ionic ferrofluids, the “depletion force” stimulates the larger ferrofluid particles, forming short chains in the absence of a magnetic field and their macroscopic properties, e.g., magnetization and optical relaxation, all result from the short chains. Ferrofluids having chainlike aggregates alone could have excellent magneto-optical effects. 相似文献
9.
A wear resistant surface composite layer on Ti–6Al–4V substrate was fabricated using powder sintering method. The surface composite layer consisted of Ti–6Al–4V matrix and different fractions of TiN particles as reinforcement phase. The surface layer and the substrate were directly bonded together while the powders were cold formed and then sintered at an elevated temperature. The two layers showed good metallurgical bond. In this study, 5%, 10% and 15% TiN weight fractions were adopted to fabricate the surface composite layer. Effects of TiN addition on the microstructure, hardness and wear resistance were investigated. It was found that the wear resistance of the surface composite layer was improved due to the addition of TiN compared to that of pure Ti–6Al–4V. 相似文献
10.
作为20世纪90年代兴起的一类连续陶瓷纤维增强陶瓷基复合材料,连续氧化铝纤维增韧氧化铝(Al2O3f/Al2O3)复合材料已经发展为与Cf/SiC、SiCf/SiC等非氧化物复合材料并列的陶瓷基复合材料。以多孔基体实现基体裂纹偏转成为Al2O3f/Al2O3复合材料主要的增韧设计方法,形成的多孔Al2O3f/Al2O3复合材料具有优异的抗氧化性能和高温力学性能,可在高温富氧、富含水汽的中等载荷工况中长时服役,是未来重要的热结构材料。经过近30年的发展,多孔Al2O3f/Al2O3复合材料已被应用于航空发动机、燃气轮机等热端部件。本文综述了多孔Al2O3f... 相似文献
11.
Tribological properties of bulk Al6061–Al2O3 nanocomposite prepared by mechanical milling and hot pressing were investigated. Al6061 chips were milled for 30 h to achieve a homogenous nanostructured powder. A 3 vol.% Al2O3 nanoparticles (∼30 nm) were added to the Al6061 after 15 and 30 h from the beginning of milling. The milling times with Al2O3 in these two samples were then 15 h and 30 min, respectively. Additionally, 3 vol.% Al2O3 (1 μm and 60 μm) was added to the Al6061 after 15 h of milling; where, the micron size Al2O3 in these two samples, was milled 15 h with the matrix. Hot pressing of milled samples was executed at 400 °C under 128 MPa pressure in a uniaxial die. The hot pressed samples were characterized by micro-hardness test, bulk density measurements, pin on disc wear test, and finally scanning electron microscopy observations. Fifteen hour-milled nanocomposite with nanoscale Al2O3, showed improvement in wear resistance and bulk density compared with that of 30 min-milled nanocomposites due to better dispersion of Al2O3 nanoparticles, improved surface quality of nanocomposite particles before pressing and more grain refinement of Al matrix. Moreover, increasing the reinforcement size increased the wear rate because of reduction in relative density, hardness and inter-particle spacing. 相似文献
12.
The subject of the work was to study the effect of Nb + Ti thin film deposited by PVD method on alumina substrates on the
wetting behavior, bond strength properties, and structure of interface in the Al/Al2O3 joints. Applying the sessile drop method, the wetting behavior of molten Al (99,999%) on coated alumina substrates was studied
in the temperature range between 953 and 1373 K under a vacuum of 0.2 mPa for 30 min of contact. The sessile drop samples
were used to examine the interface structure, shear strength, and interfacial fracture toughness under the concentrated load.
The introduction of the thin Nb + Ti film layer of 900 nm thickness: (1) greatly improves the wettability of alumina by molten
Al at above 1223 K and the shear strength of Al/Al2O3 joints produced at 1223 K, (2) has positive effect on structure transformation in the interface and leads to fabrication
of reliable metal–ceramic joints. Microstructural investigations of the interface indicated that the precipitates of Nb and
Ti-rich intermetallic phases were formed at the Al/Al2O3 interface, which influenced strengthening of these joints. Hence a conclusion can be drawn that the interface structure influences
the durability increase in Al/Al2O3 joints. 相似文献
13.
Y. Y. Chen P. C. Chen C. B. Tsai K. I. Suga K. Kindo 《International Journal of Thermophysics》2009,30(1):316-324
Thermometers consisting of RuO2–Al2O3 composite thin films were prepared by RF sputtering. It was found that different electrode-patterning techniques have dissimilar
effects on the magnetoresistance (MR) and the temperature coefficient of resistance (TCR). In general, the thermometers with
electrodes fabricated by photo-resist lithography exhibit superior performance compared to those with electrodes prepared
using a metal mask. By adjusting the relative compositions of RuO2 and Al2O3, the thermometers can be applied to a wide temperature range from 60 mK to 500 K. In a pulsed magnetic field up to 55 T,
the MR at 4.2 K of a typical thermometer for the temperature range from 1.4 K to 300 K increases linearly with magnetic field
to a maximum of ~15 %, corresponding to a temperature deviation of ~−4 %. As frequency increases from dc to 1.9 MHz, the MR
decreases from −13 % to ~ − 0.5 % at T = 1.3 K and H = 55 T. By integrating the thermometer with a heater on a sapphire chip, a micro-calorimeter can be developed and successfully
used to measure the heat capacity of small mg-sized sample. The RuO2–Al2O3 composite film can also be employed as an infrared bolometer operated at room temperature. 相似文献
14.
Al2O3颗粒对Al2O3p/Al复合材料时效析出的影响 总被引:3,自引:0,他引:3
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。 相似文献
15.
This study was undertaken to investigate the effect of strontium (0.5%) as a modifier on the microstructure and dry sliding wear behavior of A356–10%B4C particulate metal matrix composite (PMMC). The composite ingots were made by stir casting process. In this work, composite were characterized by scanning electron microscope equipped with energy dispersive spectrometer (EDS), and dry sliding wear experiment were performed in a pin-on-disc wear tester against a DIN 100Cr6 steel disc at speed of 0.5 ms−1 and normal loads of 20, 40 and 60 N. The obtained results showed that 0.5%Sr was needed to modify of silicon eutectic in A356–10%B4C cast composite. Also, the wear results showed that the addition of strontium to MMCs can lead to reduction of wear rate through strong bonding (between B4C and matrix) and silicon particle modification. Formation of compact transfer layer has been identified on the entire surface of the pins at the applied load of 60 N. It is suggested that the transfer layer which was formed under an applied load of 60 N can act as a protective layer and helps to reduce wear rate. 相似文献
16.
In this study, the formation and characterisation of Aluminium (Al)-based composites by mechanical alloying and hot extrusion were investigated. Initially, the vanadium trialuminide (Al3V) particles with nanosized structure were successfully produced by mechanical alloying and heat treatment. Al3V–Al2O3 reinforcement was synthesised by mechanochemical reduction during milling of V2O5 and Al powder mixture. In order to produce composite powders, reinforcement powders were added to pure Al powders and milled for 5?h. The composite powders were consolidated in an extrusion process. The results showed that nanostructured Al-10?wt-% Al3V and Al-10?wt-% (Al3V–Al2O3) composites have tensile strengths of 209 and 226?MPa, respectively, at room temperature. In addition, mechanical properties did not drop drastically at temperatures of up to 300°C. 相似文献
17.
Ferrous based materials manufactured by powder metallurgy (P/M) method are widely used in industry. These materials are very important because they do not require machining, have self-lubricated properties as journal bearing material, find applications in medical industry. In this study, powder metal parts were manufactured from ferrous based FeCu–Graphite composites by P/M method. Wear and mechanical test samples were manufactured and boronizing and boronizing + shot peening was applied to samples. Wear properties of these parts were investigated by wearing at 17 N load and 50 rpm on pin-on-disc wear test rig under dry conditions. Moreover, mechanical properties of powder parts were investigated in detail. 相似文献
18.
Dianran Yan Yong Yang Yanchun Dong Lei Wang Xueguang Chen Jianxin Zhang Jining He 《Materials Chemistry and Physics》2012
Fe2O3–Al composite powders were deposited onto steel substrate by plasma spraying. The reaction products of the Fe2O3–Al composite powders in the plasma flame and their solidification process were investigated. The results showed that the reaction products of the Fe2O3–Al composite powders in the plasma flame were Fe–Al–O ceramic melt and Fe melt. Fe was not always formed in the reaction products of each composite particle, and the formation of Fe was dependent on the composition distribution and the reaction kinetics process of each composite particle. The composition inhomogeneity, discontinuity and porousness of the composite particles resulted in the difference of the reaction kinetics of each composite particle and the composition difference of the droplets. Hercynite solid solution, Fe, Al2O3 and FeAl phases were formed by non-equilibrium solidification of the Fe–Al–O ceramic melt. For the smaller size droplet, when it spread on the substrate, the spreading droplet was quickly chilled to form equiaxed grains with size of 100–200 nm. Nano-sized or submicron equiaxed grains, nano-sized columnar grains and cellular structure were formed in the larger spreading droplet. Fe rich hercynite solid solution nucleated and grew preferentially and then Al rich hercynite solid solution grew, which form composition segregation in the columnar grains. The main phases in the composite coating were hercynite solid solution. 相似文献
19.
H. Doweidar 《Journal of Materials Science》2009,44(11):2899-2906
Refractive index and molar refraction of Li2O–, Na2O–, CaO–, and BaO–Ga2O3–SiO2 glasses have been used to test the validity of a structural model of silicate glasses containing Ga2O3 glasses. Ga2O3 enters these types of glass in a similar manner as Al2O3. It is assumed that, for (SiO2/Ga2O3) >1 and (Ga2O3/R2O) ≤1, Ga2O3 associates primarily with modifier oxides to form GaO4 units. The rest of modifier oxide forms silicate units with non-bridging oxygen ions. Silicate structural units have the
same factors as found for binary alkali- and alkaline earth silicate glasses. Differences between experimental and model values
suggest another structure for (Ga2O3/SiO2) ≥1. 相似文献
20.
通过混炼工艺制备了片状Al2O3填充聚全氟乙丙烯(FEP)复合材料,以颗粒状Al2O3为对比样品,研究了片状Al2O3形状和尺寸对 FEP基复合材料热导率的影响,利用SEM观察了FEP基复合材料的微观形貌。结果表明:在低填充量下,Al2O3颗粒在FEP基体中呈“海岛”状分布,没有形成连续的导热网链,但其热导率明显提高;复合材料拉伸强度与断裂伸长率随Al2O3含量的增加而减小;低填充量时复合材料热导率的提高主要来自Al2O3的微细片状结构,这种微细片状结构一方面提高了有效导热路径,另一方面增加了颗粒与基体之间接触面积,因此有利于热导率的提高。 相似文献