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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.
D. Bo?i? J. Staši? J. Ru?i? M. Vilotijevi? V. Rajkovi? 《Materials Science and Engineering: A》2011,528(28):8139-8144
Multiple hardening mechanisms of a copper matrix have been presented and discussed. The gas atomized Cu-0.6 wt.%Ti-2.5 wt.%TiB2 (Cu-Ti-TiB2) powders were used as starting materials. Dispersoid particles TiB2 were formed in situ in the copper matrix during gas atomization. The powders have been consolidated by hot isostatic pressing (HIP). Optical microscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD) analysis were performed for microstructural characterization of powders and composite compacts. High hardening of the Cu-Ti-TiB2 composite achieved by aging is a consequence of the simultaneous influence of the following factors: the development of modulated structure with metastable Cu4Ti(m) particles and in situ formed TiB2 dispersoid particles. 相似文献
3.
Particle fracture in metal-matrix composite friction joints 总被引:1,自引:0,他引:1
The influence of welding parameters, reinforcing particle chemistry and shape, matrix condition and silver interlayers on
particle fracture during similar and dissimilar friction welding of aluminium-based metal-matrix composite (MMC) base material
was investigated. Two composite base materials were examined, one containing Al2O3 particles and the other containing 72 wt% Al2O3–7 wt % Fe2O3–17 wt % SiO2–3 wt % TiO2 particles. The different material combinations comprised MMC/MMC, MMC/alloy 6061, MMC/AISI 304 stainless steel and MMC/1020
mild steel joints. Particle fracture was confined to a narrow region immediately adjacent to the dissimilar joint interface.
The calculated normal pressure for fracture of Al2O3 particles ranges from 0.56–17.58 MPa and is in agreement with an experimentally measured pressure of 1.06 MPa found during
sliding wear testing of aluminium-based composite base material. Because the lowest normal pressure applied during friction
joining was 30 MPa, particle fracture occurs very early in the joining operation (immediately following contact between the
two substrates). The application of a silver interlayer during dissimilar MMC/AISI 304 stainless steel joining decreased the
particle fracture tendency. It is suggested that the presence of a silver interlayer decreased the coefficient of friction
and lowered the stresses applied at the contact region. The particle fracture tendency was markedly increased when the MMC
material contained blocky alumina particles. However, there was negligible particle fracture when the MMC base material contained
spherical 72 wt % Al2O3–7 wt % Fe2O3–17 wt % SiO2–3 wt % TiO2 particles.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
4.
The displacement reaction between Al and SiO2 in an Al–3wt%Cu–3wt%Si–9wt%SiO2 powder mixture has been studied when the mixture had been ball-milled, and compared with the reaction in the as-mixed powder.
Diffusion couples consisting of Al/SiO2 were formed during ball milling. The size of the composite powder particles and the diffusion couples was reduced by increasing
the ball milling time. Differential thermal analysis and X-ray diffraction results showed that the displacement reaction between
Al and SiO2 did not occur in the as-mixed powder, but occurred in the as-milled powders in the temperature range of 640–680 °C. Furthermore,
the onset temperature of the displacement reaction shifted to lower temperatures after increasing the ball milling time. On
the basis of these results the milled powder was sintered at 640 °C in order to produce an Al–Cu–Si matrix composite reinforced
with homogeneously distributed submicron-sized Al2O3 particles. This is much lower than the temperature required for the same reaction in other processes which are used to produce
such composites, such as the melting infiltration process. 相似文献
5.
An as-received ultrafine-grained Cu powder and four nanostructured Cu–(2.5–10) vol%Al2O3 composite powders produced by high-energy mechanical milling of mixtures of the Cu powder and an Al2O3 nanopowder were consolidated using warm powder compaction followed by open die powder compact forging. The circular discs
produced in the experiments achieved full densification. Tensile testing of the specimens cut from the forged discs showed
that the Cu-forged disc had a fairly high yield strength of 330 MPa, UTS of 340 MPa and a plastic strain to fracture of 15%,
but the Cu–Al2O3 composite-forged discs did not show any macroscopic plastic yielding. The fracture strength of the composite-forged discs
decreased almost linearly with the increase of the volume fraction of Al2O3 nanoparticles. This study shows that a high level of consolidation of the ultrafine-grained Cu powder and the nanostructured
Cu–2.5 vol%Al2O3 composite powder has been achieved by warm powder compacting at 350 °C and powder compact forging at 500 and 700 °C. However,
this is not true for the nanostructured Cu–(5, 7.5 and 10) vol%Al2O3 composite powders, possibly due to their higher powder particle hardness at elevated temperatures in the range of 350–800 °C. 相似文献
6.
Pure Al powders were mixed with a 30 % volume fraction of Al2O3 powders having particle sizes of ~30 nm. The mixed powders were first subjected to ball milling (BM) and thereafter consolidated by high-pressure torsion (HPT) at room temperature under a pressure of 3 GPa for 10 turns. The Al–Al2O3 composite produced by BM and HPT (BM + HPT) had a more uniform dispersion of the nano-sized Al2O3 particles in the Al matrix. Hardness values of the BM + HPT composites were higher than those of the composites without BM. It is shown that the use of BM powders for HPT is more effective in achieving a uniform dispersion of the nano-sized Al2O3 particles and in improving mechanical properties of the Al–Al2O3 nanocomposites. 相似文献
7.
Rapidly solidified powders of Al–5.0Cr–4.0Y–1.5Zr (wt%) were prepared by using a multi-stage atomization-rapid solidification
powder-making device. The atomized powders were sieved into four shares with various nominal diameter level and were fabricated
into hot-extruded bars after cold-isostatically pressing and vaccum degassing process. Influence of atomized powder size on
microstructures and mechanical properties of the hot-extruded bars was investigated by optical microscopy, X-ray diffraction,
transmission electronic microscopy with EPSX and scanning electron microscopy. The results show that the fine atomized powders
of rapidly solidified Al–5.0Cr–4.0Y–1.5Zr aluminum alloy attains supersaturated solid solution state under the exist condition
of multi-stage rapid solidification. With the powder size increasing, there are Al20Cr2Y (cubic, a = 1.437 nm) and Ll2 Al3Zr (FCC, a = 0.407 nm) phase forming in the powders, and even lumpish particles of Al20Cr2Y appearing in the coarse atomized powders, as can be found in the as-cast master alloy. Typical microstructures of the extruded
bars of rapidly solidified Al–5.0Cr–4.0Y–1.5Zr aluminum alloy can be characterized by fine grain FCC α-Al matrix with ultra-fine
spherical particles of Al20Cr2Y and Al3Zr. But a small quantity of Al20Cr2Y coarse lumpish particles with micro-twin structures can be found, originating from lumpish particles of the coarse powders.
The extruded bars of rapidly solidified Al–5.0Cr–4.0Y–1.5Zr aluminum alloy by using the fine powders eliminated out too coarse
powders have good tensile properties of σ0.2 = 403 MPa, σb = 442 MPa and δ = 9.4% at room temperature, and σ0.2 = 153 MPa, σb = 164 MPa and δ = 8.1% at high temperature of 350 °C. 相似文献
8.
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
9.
It is very difficult to simultaneously refine and modify Si particles in hypereutectic Al–Si–Cu alloys to enhance their ductility.
This study investigates how nanoparticles affect Si particles during solidification in hypereutectic Al–Si–Cu alloys. 0.5
wt% γ-Al2O3 nanoparticles were added in hypereutectic Al–20Si–4.5Cu alloy melt and further dispersed through an ultrasonic-cavitation-based
technique. The as-cast Al–20Si–4.5Cu–Al2O3 nanocomposites showed marked enhancements in both ductility and strength. The ductility of Al2O3 nanocomposite was more than two times higher than that of the monolithic alloy without the nanoparticles. Microstructural
analysis with optical and scanning electron microscopy revealed that both the primary and eutectic Si particles were significantly
refined. The primary Si particles were refined from star shapes to polygon or blocky shapes, and their edges and corners were
much smoother. The large plate eutectic Si particles were also modified into the fine coralline-like ones. The porosity of
alloy was also reduced with the addition of γ-Al2O3 nanoparticles. Study suggests that γ-Al2O3 nanoparticles simultaneously refine and modify Si particles as well as reduce porosity in cast Al–20Si–4.5Cu, resulting in
unusual ductility enhancement that could have great potential for numerous applications. 相似文献
10.
Soda alumina borosilicate glasses of composition (24-y)Na2O·yAl2O3·14B2O3·37SiO2·25Fe2O3, y = 8, 12, 14, 16 mol%, were melted using Fe2O3 as raw material. Besides, samples with y = 12 and Fe2O3 concentrations of 14.32, 17.8, and 25.0 mol% were prepared from FeC2O4·2H2O as raw material. The X-ray diffraction analyses showed the presence of magnetite for the samples from all the investigated
compositions. Transmission electron microscopy (TEM) evidenced that all the samples are phase separated and droplets in the
diameter range 100–1000 nm, enriched in iron, are formed. Inside these droplets, numerous small magnetite particles, with
size in the 25–40 nm interval, are crystallized. 相似文献
11.
Effects of calcination on catalytic activity for steam reforming of methanol (SRM) over an Al–Cu–Fe quasicrystal (QC) leached
with NaOH aq. have been investigated in terms of microstructure with X-ray diffraction and transmission electron microscope
(TEM). Calcination at 600 °C in air drastically improved the catalytic activity of the leached QC. TEM observations on cross-section
of the samples revealed that cubic Cu
x
Fe3-x-y
Al
y
O4 spinel was formed at the outermost layer of the leached QC after calcinations. Prior to the catalytic reaction, the Cu
x
Fe3-x-y
Al
y
O4 spinel decomposed to a composite where fine Cu nanoparticles dispersed in (Fe,Al)3O4 matrix under H2 treatment at 300 °C. Drastic increase in catalytic activity is responsible for the fine Cu nanoparticles in the composite.
The Cu nanoparticles sit along the same orientation with (Fe,Al)3O4, e.g., Cu [013]//(Fe,Al)3O4 [013] and Cu [200]//(Fe,Al)3O4 [400]. This orientation relationship may stabilize the Cu nanoparticles through a bonding of Cu–O–Fe. 相似文献
12.
Xiumin Yao Shouhong Tan Xiangyu Zhang Zhengren Huang Dongliang Jiang 《Journal of Materials Science》2007,42(13):4960-4966
SiC reticulated porous ceramics (SiC RPCs) was fabricated with polymer replicas method by using MgO–Al2O3–SiO2 additives as sintering aids at 1,000∼1,450 °C. The MgO–Al2O3–SiO2 additives were from alumina, kaolin and Talc powders. By employing various experimental techniques, zeta potential, viscosity
and rheological measurements, the dispersion of mixed powders (SiC, Al2O3, talc and kaolin) in aqueous media using silica sol as a binder was studied. The pH value of the optimum dispersion was found
to be around pH 10 for the mixtures. The optimum condition of the slurry suitable for impregnating the polymeric sponge was
obtained. At the same time, the influence of the sintering temperature and holding time on the properties of SiC RPCs was
investigated. According to the properties of SiC RPCs, the optimal sintering temperature was chosen at 1,300 °C, which was
lower than that with Al2O3–SiO2 additives as sintering aids. 相似文献
13.
E. V. Dudnik A. V. Shevchenko A. K. Ruban V. P. Red’ko L. M. Lopato 《Inorganic Materials》2010,46(2):172-176
We have studied the properties of nanocrystalline ZrO2〈3 mol % Y2O3〉 and 90 wt % ZrO2〈3 mol % Y2O3〉-10 wt % Al2O3 powders prepared via hydrothermal treatment of coprecipitated hydroxides at 210°C. The results demonstrate that Al2O3 doping raises the phase transition temperatures of the metastable low-temperature ZrO2 polymorphs and that the structural transformations of the ZrO2 and Al2O3 in the doped material inhibit each other. 相似文献
14.
Toyohiko J. Konno Rimi Nishio Satoshi Semboshi Tetsu Ohsuna Eiji Okunishi 《Journal of Materials Science》2008,43(11):3761-3768
Aging behavior of Cu–3 at.%Ti–4 at.%Al alloy at 723 K has been examined from mechanical, electrical, and microstructural points
of view. Compared with binary Cu–3 at.%Ti alloy, the electrical conductivity improved six times to about 6%IACS (international
annealed copper standard); whereas the peak hardness decreased from 280 to 180 Hv. The major strengthening phase is the tetragonal
α-Cu4Ti, which forms not via spinodal decomposition but based on the nucleation and growth mechanism. The precipitates grow in
the c direction of the tetragonal phase, which lies along one of the
axes of the matrix fcc Cu phase. This growth mode minimizes the strain energy arising from the lattice mismatch of about
2% between the matrix and precipitate; and results in a square rod shape, which reaches about 50 nm in length after 100 h
anneal. Another precipitating phase is AlCu2Ti (D03, Strukturbericht notation), with the major habit plane close to {110} of the fcc Cu matrix. The orientation relationship
was not definitely determined, but it was found that the angle between the 100 and 110 poles of the matrix and precipitates,
respectively, is about 5°, while the angle between the two 001 axes being about 7°. It was suggested that the formation of
this ternary phase reduced the solute Ti concentration, leading to the decrease in the resistivity. 相似文献
15.
The aim of the article was to evaluate the microstructural parameters of Cu–Al2O3 dispersion strengthened materials with different volume fraction of Al2O3 phase. For analyses of dispersoids Al2O3, the extraction carbon replica was used. The distribution of Al2O3 particles in the matrix was estimated by three methods (quadrant count method, polygonal method, and by interparticle distances),
these methods showed that particle distribution in material with 1 vol.% of Al2O3 is very close to the Poisson point process (PPP), which is a model of randomly distributed points. Particle distributions
in materials with 8 and 10 vol.% of Al2O3 achieve features of regularity proved mainly by the spherical contact distance. 相似文献
16.
The structure of Al2O3-SiO2 sub-micron powders prepared by oxidation of mixed aluminium-silicon halides in an oxygen-argon high frequency plasma flame has been studied. The powders were completely amorphous up to at least 52 wt % Al2O3 and partially amorphous in the range 52 to 88 wt % Al2O3. The crystalline phase was mullite up to 75 wt % Al2O3 but at higher Al2O3 contents a metastable solid solution of SiO2 in -Al2O3 was observed in addition to mullite. Amorphous particles crystallized to mullite on heating to 1000°C, independently of composition. Extension of glass formation towards the high Al2O3 end of the Al2O3-SiO2 system as the cooling rate is increased and particle size decreased, may be explained by the effect of viscosity on the nucleation rate of mullite from liquid, for Al2O3 contents up to 60 wt %. The viscosity change is relatively small as the Al2O3 content is increased beyond 60% and it is suggested that the change in nucleus-liquid interfacial energy with composition is the predominant factor controlling nucleation rate in this range. At Al2O3 concentrations greater than approximately 80 wt %, -Al2O3 is the phase which nucleates from the melt. A double DTA peak was observed for powders containing more than 80 wt % Al2O3. The lower temperature peak is believed to arise from the formation of mullite from a metastable solution of SiO2 in -Al2O3, and the higher temperature peak from crystallization of mullite from the amorphous phase. The presence of SiO2 in solution in metastable Al2O3 increases the temperature of transformation to -Al2O3 to greater than 1500° C compared with 1230° C for pure Al2O3. 相似文献
17.
The effect of aluminum on the precipitation hardening of Cu–Ni–Zn alloys with varying aging temperatures and times was investigated
in this article, in the hope to achieve better mechanical properties. Vickers hardness, tensile, and electrical conductivity
tests were carried out to characterize the properties of the Cu–Ni–Zn alloys with or without an addition of aluminum subjected
to different aging treatments. The results show that an addition of 1.2 wt% aluminum can play an influential role in the precipitation
hardening of the Cu–Ni–Zn alloys. For example, it can increase the peak hardness from 58 Hv for the solution-treated Cu–10Ni–20Zn
alloy to 185 Hv for the solution-treated Cu–10Ni–20Zn–1.2Al alloy during aging at 500 °C. The yield strength, tensile strength,
and electrical conductivity of the Cu–10Ni–20Zn–1.2Al alloy subjected to suitable treatments under prior cold-rolled and aged
conditions can reach 889 MPa, 918 MPa, and 10.96% IACS, respectively, being much higher than those of the relevant alloy without
aluminum and comparable to those of the Cu–Be alloys (C17200 and C17510). According to the transmission electron microscope
observations, it was found that formation of nanosized precipitates with the L12-type ordered lattice results in precipitation hardening, and an orientation relationship of
[011]\textp//[011]\textm [011]_{\text{p}}//[011]_{\text{m}} and
(100)\textp//(200)\textm (100)_{\text{p}}//(200)_{\text{m}} exists between the precipitates and the α-Cu matrix. 相似文献
18.
S N Vaidya 《Bulletin of Materials Science》1999,22(3):287-293
We report first observation of new polymorphs of Al2O3 and Fe2O3 in specimens of xerogelγ Al2O3 andγ Fe2O3 quenched from high pressures and temperatures. At about 5 GPa and 1400°C, xerogel gamma alumina (XGA) transformed into a
polymorphic mixture of phasesα Al2O3, B Al2O3 and C Al2O3, while XGA containing 1 wt% Cr2O3 transformed into a mixture of phasesαAl2O3, H Al2O3 and k′ Al2O3. The phases B Al2O3, C Al2O3 and H Al2O3 have the monoclinic-, cubic- and hexagonal-rare earth sequioxide (Ln2O3) type structure, respectively. At 5·2 GPa and 1450°C, XGA yielded a mixture ofα Al2O3 and hexagonalμ Al2O3. At STP, the phaseμ Al2O3 was found to transform to another hexagonal phaseλAl2O3 over a 10 week period.
At 5·2 GPa and 900°C,γ Fe2O3 showed transition to a new phase H Fe2O3 which probably has an 8 layer close packed structure. In nanocrystalline TiO2, only the anatase to rutile transition was found. The results are discussed using the free energy vs temperature diagram
for xerogel and nanocrystalline materials. 相似文献
19.
Ag/γ–Al2O3 with silver loading of 3 wt.% were prepared by the solvothermal-calcination reaction of AgNO3 in mixed water-alcohol solutions at 50–250 °C for 0–120 min, followed by calcinations at 550 °C for 2 h using γ-Al2O3 (SSA: 120–409 m2 g−1), γ-AlOOH (SSA: 270 m2 g−1), Al(OH)3 (SSA 10 m2 g−1), Al(OCH(CH3)2)3 and Al(NO3)3 as an aluminum source. The resultant product produced by the solvothermal reaction was Ag/γ–AlOOH even though a different
aluminum source was used and Ag/γ–AlOOH was converted to Ag/γ–Al2O3 by the following calcinations. However, the characteristics of them changed greatly depending on the alumina source. The
deNO
x
catalytic performance of Ag/γ–Al2O3 also greatly changed depending on the aluminum precursor and solvothermal solvent in the order γ-AlOOH = γ-Al2O3 >> Al(OCH(CH3)2)3 >> Al(NO3)3 > Al(OH)3 and methanol = ethanol > 1-propanol > butanol >> hexanol, since the amount and size of silver particle impregnated and specific
surface area of the product changed markedly. Ag/γ–Al2O3 prepared by solvothermal-calcination method consisted of homogeneously dispersed fine particles of silver and showed better
performance for NO
x
decomposition than that by conventional impregnation-calcination method. 相似文献
20.
A simple preparation of KNbO3 powders was proposed by an alternative approach of solid-state reaction. Stoichiometric niobium oxalate and potassium acetate
were mixed in water and then dried. It was demonstrated that an ion-exchange reaction occurred with the formation of K[NbO(C2O4)2]·nH2O intermediate. The single-phase KNbO3 powders were synthesized when K[NbO(C2O4)2]·nH2O intermediate was calcined between 500 and 800 °C for 3 h. KNbO3 powders obtained at 500 °C are determined as orthorhombic structure with an average particle size of 20–50 nm by X-ray diffraction,
scanning electron microscope (SEM), and transmission electron microscopy (TEM) analysis. The morphologies of KNbO3 obtained at different temperatures were observed by SEM and TEM analysis. The average band gap energy is estimated to be
3.16 eV by UV–vis diffuse reflectance spectra. 相似文献