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1.
Two methods were used to obtain amorphous aluminium alloy powder: gas atomization and melt spinning. The sprayed powder contained only a small amount of the amorphous phase and therefore bulk composites were prepared by hot pressing of aluminium powder with the 10% addition of ball milled melt spun ribbons of the Al84Ni6V5Zr5 alloy (numbers indicate at.%). The properties were compared with those of a composite containing a 10% addition of Al2O3 ceramic particles. Additionally, a composite based on 2618A Al alloy was prepared with the addition of the Al84Ni6V5Zr5 powder from the ribbons used as the strengthening phase. X-ray studies confirmed the presence of the amorphous phase with a small amount of aluminium solid solution in the melt spun ribbons. Differential Scanning Calorimetry (DSC) studies showed the start of the crystallization process of the amorphous ribbons at 437 °C. The composite samples were obtained in the process of uniaxial hot pressing in a vacuum at 380 °C, below the crystallization temperature of the amorphous phase. A uniform distribution of both metallic and ceramic strengthening phases was observed in the composites. The hardness of all the prepared composites was comparable and amounted to approximately 50 HV for those with the Al matrix and 120 HV for the ones with the 2618A alloy matrix. The composites showed a higher yield stress than the hot pressed aluminium or 2618A alloy. Scanning Electron Microscopy (SEM) studies after compression tests revealed that the propagation of cracks in the composites strengthened with the amorphous phase shows a different character than these with ceramic particles. In the composite strengthened with the Al2O3 particles cracks have the tendency to propagate at the interfaces of Al/ceramic particles more often than at the amorphous/Al interfaces. 相似文献
2.
《Composites Science and Technology》2006,66(7-8):1056-1062
The presence of Al4C3 in Al/SiC composites may activate degradation of the material by its interaction with water; even moisture may cause its environmental degradation. It has been demonstrated that incorporation of 6 vol% SiO2 powders into SiCp preforms before processing by pressureless infiltration prevents formation of Al4C3. Analysis by electron back-scattered diffraction confirms that regardless of its crystal structure (α-quartz or α-cristobalite), SiO2 completely reacts to form MgAl2O4. The metal/composite interface microstructure condition of the specimens processed under the most severe conditions (1100 °C for 60 min), four months later confirms the effectiveness of the SiO2 powders. 相似文献
3.
《Materials Research Bulletin》2006,41(9):1622-1630
The effects of doping 60 P2O5–40 Fe2O3 (mol%) glasses with 5–10 mol% SiO2, Al2O3 or B2O3 on their thermal stability, iron environments and redox were investigated. Thermal stability improved markedly with 5% dopant addition in the order Al2O3 > SiO2 > B2O3 ≫ base glass. Solubility of pro rata additions when melted at 1150 °C was 5–10% SiO2, <5% Al2O3, and >10% B2O3. It was possible to dissolve 5% Al2O3 by replacing Fe2O3. These additions generally had little effect on dilatometric measurements and iron environments, however the Fe2+/ΣFe redox ratio increased in the order base glass < Al2O3 < SiO2 < B2O3. This behaviour was broadly consistent with the effects of glass basicity. The increased thermal stability of these glasses may improve their suitability for applications such as waste immobilisation or sealing. 相似文献
4.
In this study, Al2O3 particles were employed to improve the microstructure of LM24 and therefore, to increase the yield strength and tensile strength of this kind of alloy. In situ Al2O3 particles were obtained by direct reaction between oxygen and Al melt at 750–800 °C. Microstructure examination shows that the size of in situ formed Al2O3 particles was about 1–2 μm, and interestingly, with addition of in situ Al2O3 particles, the coarse primary Si phase was disappeared completely. More important, the yield strength and the tensile strength of Al2O3/LM24 are increased by 52 MPa, 16 MPa than that of LM24 alloy with 0.1% Sb addition. The value of 181 MPa and 315 MPa is for yield strength and tensile strength of Al2O3/LM24 respectively. Besides, the yield strength and tensile strength are 180 MPa and 314 MPa respectively for Al2O3/LM24 alloy after remelting and casting. This verifies that the improvement of mechanical properties of such kind of material possesses stability and reliability. 相似文献
5.
《Materials Chemistry and Physics》2001,67(1-3):243-248
Displacement reaction constitutes a novel and specialized reaction-induced processing technique which allows the fabrication of a composite in net-shape. Composite containing α-Al2O3 and Al, in which both the phases are continuous, were formed by a displacement reaction between silica shapes and molten aluminium isothermally at temperatures between 1173 and 1573 K. Soaking periods varied between 0.2 and 48 h at each of these peak temperatures. The course of reaction was followed by microstructure evaluation of the products as observed at different time intervals of reaction processing. These specimens were analysed for phase evolution by XRD, extent of reaction and microstructure by optical microscopy and composition profile across the reaction zone by electron probe microanalyzer (EPMA). The product obtained on completion of reaction consisted of 74% α-Al2O3 and 26% Al (Si) by volume, and the phase were co-continuous. Grain size of % α-Al2O3 increased with an increase in forming temperature. The remarkable features of this forming technique are that the product has the same shape as that of the silica preform and it undergoes an isotropic linear shrinkage of barely over 1%. The formation of the composite and the microstructure evolution are discussed. Some properties of the product are presented. 相似文献
6.
《材料与设计》2015
A low-temperature ceramic–metal joining technique was successfully developed to produce a vacuum-tight Al2O3 ceramic and 5A05 aluminum alloy joint, with leak rates of less than 1.0 × 10− 9 Pa∙m3/s. This involved two steps: active metallization of the Al2O3 ceramic surface using Ag–Cu–TiH2–B composite filler, followed by diffusion brazing of metallized Al2O3 ceramic and 5A05 alloy at 530 °C. The microstructure, interfacial reactions and mechanical properties of the actively metallized Al2O3 ceramic and diffusion-brazed Al2O3/5A05 joint were investigated. The joint properties were determined by the formation of a continuous Ti3Cu3O reaction layer adjacent to Al2O3 ceramic, in situ synthesized TiB whiskers in the brazing seam, and dissolution thickness of 5A05 alloy. The maximum shear strength of the bonded joints reached 70 MPa, while fracture propagated in the Al2O3 substrate, with a bowed crack path. A model for quantitatively evaluating the dissolution thickness of 5A05 aluminum alloy during diffusion brazing process was established. 相似文献
7.
《Materials Science and Engineering: A》2007,443(1-2):296-300
The (Al2O3 + Ni) composite, (Al2O3 + Ni)/Ni and Al2O3/(Al2O3 + Ni)/Ni laminated materials were prepared by aqueous tape casting and hot pressing. Results indicated that the (Al2O3 + Ni) composite had higher strength and fracture toughness than those of pure Al2O3. The fracture toughness of (Al2O3 + Ni)/Ni and Al2O3/(Al2O3 + Ni)/Ni laminated materials was higher than not only those of pure Al2O3, but also those of Al2O3/Ni laminar with the same layer numbers and thickness ratio. It was found that the toughness of the Al2O3/(Al2O3 + Ni)/Ni laminated material with five layers and layer thickness ratio = 2 could reach 16.10 MPa m1/2, which were about 4.6 times of pure Al2O3. The strength and toughness of the (Al2O3 + Ni)/Ni laminated material with three layers and layer thickness ratio = 2 could reach 417.41 MPa and 12.42 MPa m1/2. It indicated the material had better mechanical property. 相似文献
8.
In this research, in situ fabrication of Al3V based nanocomposite and its formation mechanism have been investigated. In order to synthesize Al3V/Al2O3 nanocomposite, a mixture of Al and V2O5 powders was subjected to high-energy ball milling and the nanocomposite was produced through a mechanochemical reaction. The produced structure was isothermally heat-treated at 500–600 °C for 0.5–2 h under argon atmosphere. In order to evaluate the structural changes during milling and annealing, the synthesized powders were characterized by X-ray diffraction (XRD). Moreover, the powder morphological changes were studied by scanning electron microscopy (SEM). It was observed that the reaction between Al and V2O5 occurred after about 30 min and, the Al3V and Al2O3 were formed in nanocrystalline structure with the continuing mechanical milling. Calculation of adiabatic temperature confirmed that reaction took place in combustion mode. In final stage of milling up to 40 h; it was observed that the Al3V decomposed to Al and V so that the optimum time of milling to achieve fabrication of nanocomposite was determined to be about 20 h. Calculations based on Miedema’s model verified partial disordering of Al3V during further milling and annealing of as-milled powder at 600 °C led to the ordering of Al3V. The crystallite size of Al3V and Al2O3 after annealing at 600 °C for 2 h remained in nanometer scale. So the final product appeared to be stable even after annealing. 相似文献
9.
《Materials Science and Engineering: A》2006,415(1-2):177-183
Al2O3 thin films were deposited on a Ti3Al based alloy (Ti–24Al–14Nb–3V–0.5Mo–0.3Si) by sol–gel processing. Isothermal oxidation at temperatures of 900–1000 °C and cyclic oxidation at 800–900 °C were performed to test their effect on the oxidation behavior of the alloy. Results of the oxidation tests show that the oxidation parabolic rate constants of the alloy were reduced due to the applied thin film. This beneficial effect became weaker after longer oxidation time at 1000 °C. TiO2 and Al2O3 were the main phases formed on the alloy. The thin film could promote the growth of Al2O3, causing an increase of the Al2O3 content in the composite oxides, sequentially decreased the oxidation rate. Nb/Al enriched as a layer in the alloy adjacent to the oxide/alloy interface in both the coated and uncoated alloy. The coated thin film decreased the thickness of the Nb/Al enrichment layer by reducing the scale growth rate. 相似文献
10.
《材料与设计》2015
Three kinds of A356 based composites reinforced with 3 wt.% Al2O3 (average particle size: 170 μm), 3 wt.% SiC (average particle size: 15 μm), and 3 wt.% of mixed Al2O3–SiC powders (a novel composite with equal weights of reinforcement) were fabricated in this study via a two-step approach. This first process step was semi-solid stir casting, which was followed by rolling as the second process step. Electroless deposition of a copper coating onto the reinforcement was used to improve the wettability of the ceramic particles by the molten A356 alloy. From microstructural characterization, it was found that coarse alumina particles were most effective as obstacles for grain growth during solidification. The rolling process broke the otherwise present fine silicon platelets, which were mostly present around the Al2O3 particles. The rolling process was also found to cause fracture of silicon particles, improve the distribution of fine SiC particles, and eliminate porosity remaining after the first casting process step. Examination of the mechanical properties of the obtained composites revealed that samples which contained a bimodal ceramic reinforecment of fine SiC and coarse Al2O3 particles had the highest strength and hardness. 相似文献
11.
《Composites Part A》2007,38(2):615-620
Al2O3–FeCrAl composites were fabricated by mixing Fe2O3, Al and Cr powders and then reactive hot pressing. The high temperature alloy FeCrAl was formed by the reaction of extra Al, Cr and the Fe reduced from Fe2O3. The Al2O3–FeCrAl composites with various Al2O3 fractions were successfully fabricated by the proper addition of extra Fe, Cr, Al or Al2O3 powders. A five-layer functionally graded material of YSZ–FeCrAl was fabricated using the Al2O3–FeCrAl composites with compositions of 25, 53.2 and 75 vol.% Al2O3 as interlayer. The results from XRD analysis, optical microscope observation and thermal cycling test show that the composites fabricated by this method consist of α-Al2O3 phase and (Fe, Cr, Al) solid solution. The α-Al2O3 grain formed by this in-situ reaction between Fe2O3 and Fe is ultrafine and uniform distribution. The three-point bending strength is 305.0 MPa for the composite with 53.2 vol.% Al2O3 prepared by the reactive hot pressing, about 20% higher than that of the composite with same composition prepared by ex situ hot pressing method (252.0 MPa). No cracking was found in the functionally graded materials after 10 thermal cycles up to 1000 °C due to the better metal–ceramic bond, continuous in microstructure at interface of FGM and good oxidation resistance component FeCrAl alloy formed in the FGM. 相似文献
12.
《Materials Letters》2006,60(13-14):1651-1653
TiAl-based specimens were siliconized with two different kinds of cementation respectively, one is 23 vol.% Si + 77 vol.% Al2O3, and the other is 23 vol.% Si + 77 vol.% ZrO2. SEM observation showed that a Ti5Si3-based layer, in which some Al2O3 particles dispersed, formed on the surface after siliconization. Further observation showed that an extra outer Al2O3 layer existed on the surface of specimens siliconized with 23 vol.% Si + 77 vol.% Al2O3, while no such Al2O3 layer was found in specimens siliconized with 23 vol.% Si + 77 vol.% ZrO2. The cyclic oxidation test performed at 900 °C shows that the oxidation resistance was significantly improved by siliconizing. By comparison, the specimens that siliconized with 23 vol.% Si + 77 vol.% Al2O3 exhibits a better oxidation resistance than that with 23 vol.% Si + 77 vol.% ZrO2. It was deduced that the extra outer Al2O3 layer is beneficial to the oxidation resistance of siliconized TiAl-based alloy. 相似文献
13.
We report results on the processing and characterization of different glass preforms and single core fibers within the SiO2–Na2O–B2O3–Er2O3–P2O5–Al2O3 system. Micro-Raman spectroscopy was used to identify post-draw structural modification. The differences in the micro-Raman spectra recorded on the preform and on the fiber glass were attributed to a change in the structure induced by the drawing process. Changes in the silicate network organization and small scale molecular orientation within the glass matrix are suspected to occur during the fiber drawing process. We found that the extent in the changes between the preform and fiber properties depend on the glass composition. The glass network of the Al-containing fiber is expected to be less sensitive to the drawing process than that of the fiber matrix as the network of this Al-containing fiber is formed by a larger number of Si-BO units in the network and neutral three-coordinated boron compared to the network of the fiber matrix. From the micro-Raman spectra, formation of small crystals is suspected to occur in the P-containing glasses during the fiber drawing process. The resulting fibers were found to have propagation losses at 1330 nm and Er3+ absorption between (7 ± 1) and (25 ± 1) dB/m and (36 ± 1) and (47 ± 1) dB/m, respectively, depending on the glass composition. 相似文献
14.
Highly porous Al2O3 scaffolds were prepared from natural cellulosic sponges via pyrolysis and Al-vapour phase infiltration. Subsequent oxidation and sintering in air resulted in porous Al2O3 ceramics with an open cellular morphology and a total porosity of 95%. The Al2O3-sponges were immersed in highly supersaturated simulated body fluid (5 × SBF) solutions with different Mg2+ and HCO3− concentrations. After soaking of the porous Al2O3 sponges for 4 days a homogeneous calcium phosphate layer with a thickness of approximately 2 μm and a Ca : P ratio of 1.62 (apatite) was found. 相似文献
15.
Using the coal fly ash (FA), pure-form Na-A and -X zeolites were synthesized by two-step process. The FA was pretreated in aqueous NaOH solution under stirring condition at 85 °C for 18 h. The amorphous aluminosilicate of FA was dissolved during pretreatment. Increasing the stirring speed accelerated the dissolution of FA and increased Si4+ and Al3+ concentrations in the solution. This fact indicated that the stirring during pretreatment significantly affected on the dissolution of FA. After pretreatment, remaining FA was removed and aqueous NaAlO2 solution was added to the residual solution to control the molar ratio SiO2/Al2O3 of 0.5–4.5. After aging the resultant at 85 °C for 24 h, white precipitates were generated over the whole SiO2/Al2O3 range. Increment of Si4+ concentration by stirring during pretreatment increases the yield of the product. At SiO2/Al2O3 = 0.5, the material was identified as Na-A zeolite with a trace amount of hydroxysodalite. A single phase Na-A zeolite was obtained at SiO2/Al2O3 = 1.0. The Na-X zeolite was emerged at SiO2/Al2O3 ? 2.0. At SiO2/Al2O3 = 4.5, a single phase Na-X zeolite was formed. The cation exchange capacity of synthetic single phase Na-A and -X zeolites was respectively 4.78 and 3.88 meq./g. 相似文献
16.
In this work, Al2O3/Co nanocomposite was successfully prepared by mechanochemical reaction between Co3O4 and Al powders in a planetary high energy ball mill. The mechanism of the reaction was dealt using X-ray diffraction (XRD), differential thermal analysis (DTA), and thermodynamics calculations. It was found that Co3O4 reacts with Al through a self-sustaining combustion reaction after an incubation period of 50 min and the reaction between Co3O4 and Al involves two steps. First, Co3O4 reacts with Al to form CoO and Al2O3 at the temperature around melting point of Al, and at higher temperature, CoO reacts with remaining Al to form Co and Al2O3. Mechanical activation process decreases the reaction temperature from 1041 °C for as-received Co3O4 and Al powder mixture to 869 °C for 45 min milled powders. After annealing of powder milled for 12 h, no phase transformation has been detected. The crystallite sizes of both α-Al2O3 and Co remained in nanometeric scale after annealing at 1000 °C for 1 h. 相似文献
17.
The effect of titanium additions on the interface and mechanical properties of infiltrated Cu8 wt%Al–Al2O3 composites containing 57 ± 2 vol% ceramic are investigated, exploring two different Al2O3 particle types and four different Ti concentrations (0, 0.2, 1, 2 wt%Ti). Addition of 0.2 wt%Ti leads to the development of a thin (5–10 nm) layer enriched in Ti at the interface between Cu alloy and Al2O3 particles; this Ti concentration produces the best mechanical properties. With higher Ti-contents Ti3(Cu, Al)3O appears; this decreases both the interface and composite strength. Composites reinforced with vapor-grown polygonal alumina particles show superior mechanical properties compared to those reinforced by angular comminuted alumina particles, as has been previously documented for aluminum-based matrices. Micromechanical analysis shows that damage accumulation is more extensive, as is matrix hardening by dislocation emission during composite cooldown, in the present Cu8 wt%Al matrix composites compared with similarly reinforced and processed Al-matrix composites. 相似文献
18.
A zirconia/alumina nanocomposite stabilized with cerium oxide (Ce-TZP/Al2O3 nanocomposite) can be a good substitute as reinforcement in metal matrix composites. In the present study, the effect of the amount of 10Ce-TZP/Al2O3 particles on the microstructure and properties of Al/(10Ce-TZP/Al2O3) nanocomposites was investigated. For this purpose, aluminum powders with average size of 30 μm were ball-milled with 10Ce-TZP/Al2O3 nanocomposite powders (synthesized by aqueous combustion) in varying amounts of 1, 3, 5, 7, and 10 wt.%. Cylindrical-shape samples were prepared by pressing the powders at 600 MPa for 60 min while heating at 400–450 °C. The specimens were then characterized by scanning and transmission electron microscopy (SEM and TEM) in addition to different physical and mechanical testing methods in order to establish the optimal processing conditions. The highest compression strength was obtained in the composite with 7 wt.% (10Ce-TZP/Al2O3) sintered at 450 °C. 相似文献
19.
《Materials Research Bulletin》2003,38(9-10):1509-1517
Mechanical properties of in-situ toughened Al2O3/Fe3Al nano-/micro-composites were measured. Effects of Fe3Al content, sintering temperature and holding time on properties and microstructure of the composites were investigated. The addition of Fe3Al nano-particles decreased the aspect ratio and grain size of Al2O3, and changed the fracture mode of composites. The maximum bending strength and fracture toughness were 832 MPa and 7.96 MPa m1/2, which were obtained in Al2O3/5 wt.% Fe3Al sintered at 1530 °C and Al2O3/10 wt.% Fe3Al sintered at 1600 °C, respectively. Compared to monolithic alumina, the strength increased by 132% and the toughness increased by 73%. The improvement in the mechanical properties of the composites was attributed to the change in fracture mode from intergranular fracture to transgranular fracture, the “in-situ reinforced effect” arising from the platelet grains of Al2O3 matrix, refined microstructure by dispersoids, as well as crack deflection and bridging of intergranular and intragranular Fe3Al. 相似文献
20.
《低温学》2017
Mechanical and electrical properties of in-situ Al–Al2O3 metal matrix composites (MMCs) fabricated by powder metallurgy approach using different aluminium powders of particle size 0.8–21 µm and purity 99.8–99.996% were examined. Hot working powder consolidation by vacuum hot pressing at 270 °C and direct extrusion at 425 °C and reduction ratio of 7:1 were applied. Subsequently, extruded composite rods with the diameter of 7.5 mm were cold worked by groove rolling and rotary swaging to the wires with the diameter of 1.1 mm. Detailed microstructural characterization of composite materials was carried out. Stress-strain characteristics of composite wires were measured at 77 and 300 K. In addition, resistivity of all wires were measured by four-probe method between 25 and 300 K and eddy current losses at frequency 72 Hz and temperatures between 18 and 77 K. Obtained results clearly showed that properly designed Al–Al2O3 MMC materials can be utilized at low temperatures e.g., for the thermal stabilization of superconducting wires. 相似文献