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1.
《Canadian Metallurgical Quarterly》2013,52(4):313-320
AbstractAn investigation has been made of grain boundaries in aluminum-magnesium alloys in the stress-corrosion-susceptible and non-susceptible conditions, to elucidate the structure of the type of boundary found in susceptible alloys; it appears after chemical etching as a continuous groove when viewed under the optical microscope.Vacuum cathodic etching was used to reveal the boundaries, and carbon replicas were examined by electron microscopy. The boundaries were found to contain either a fine, discontinuous precipitate, or no precipitate at all. In no case was a continuous grain-boundary precipitate observed.These observations were substantiated by an examination of similar boundaries in electrothinned samples by transmission electron microscopy. 相似文献
2.
《钢铁冶炼》2013,40(8):621-632
AbstractThe aim of this paper was to investigate the effect of oxygen content and temperature on the formation of oxide scales of four different steel grades. Thermo gravimetric experiments were carried out. Small samples of low carbon steels with different compositions were exposed to a gas containing a certain amount of oxygen and at temperatures in the range of 1373–1623 K. The mass gain of the steel sample was recorded. On the basis of the oxidation curves, the parabolic rate constants were reported. Post-experimental investigation of the samples was performed using scanning electron microscope and light optical microscope techniques. The results were compared with the scanning electron microscopy graphs of the steel samples taken from the real industrial reheating furnace. 相似文献
3.
Thin ribbons of the metallic glass Mg65Cu25Y10, obtained by spinning, were saturated with atomic hydrogen from electrochemical decomposition of water. The maximum amount of absorbed hydrogen was 4 mass %. The hydrogen content was determined by hot extraction. We studied the microstructure of samples with different hydrogen contents by x-ray phase analysis (from the change in the diffuse maximum), atomic force microscopy, scanning electron microscopy, and transmission electron microscopy. When the hydrogen content increases up to 3.6 mass %, the amorphous structure of the Mg65Cu25Y10 alloy is converted to a nanocrystalline structure, with formation of magnesium and yttrium hydrides at room temperature. 相似文献
4.
Thin ribbons of the metallic glass Mg65Cu25Y10, obtained by spinning, were saturated with atomic hydrogen from electrochemical decomposition of water. The maximum amount of absorbed hydrogen was 4 mass %. The hydrogen content was determined by hot extraction. We studied the microstructure of samples with different hydrogen contents by x-ray phase analysis (from the change in the diffuse maximum), atomic force microscopy, scanning electron microscopy, and transmission electron microscopy. When the hydrogen content increases up to 3.6 mass %, the amorphous structure of the Mg65Cu25Y10 alloy is converted to a nanocrystalline structure, with formation of magnesium and yttrium hydrides at room temperature. 相似文献
5.
X. D. Zhang F. C. Grensing F. Meisenkothen G. Meyrick H. L. Fraser J. M. K. Wiezorek 《Metallurgical and Materials Transactions A》2000,31(11):2963-2971
The microstructure of cast and extruded in-situ Al-Be alloys, of compositions of Be-37Al-3Ni (wt pct) and Be-34Al-2Ni-2Ag-2Si (wt pct), was investigated using optical microscopy,
scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The study indicates that both the Be and Al
phases are continuous. The Be phase has a coarse dendritic structure in the as-cast material. Fractographic analysis of failed
tensile specimens tested at room temperature revealed basal-plane cleavage failure of the Be phase and ductile failure of
the Al phase. A significant number of deformation twins were observed in the Be phase when the tensile loading axis was parallel
to the Be dendrite growth axis. An additional fracture mode was observed in the samples tested at elevated temperatures. At
elevated temperatures, decohesion of the Al-Be interface was observed on the fracture surface. This phenomena was observed
to increase as the test temperature increased from 150 °C to 315 °C. A high density of dislocations with a tangled morphology
were observed in the Al phase after the tensile test. These were determined to be associated with easy slip of 1/2〈101〉-type
dislocations. The limited ductility of the Be phase was attributed to the predominant basal slip of 〈a〉-type dislocations, b = 1/3〈1120〉, and the lack of dislocations with 〈c〉 components. However, a significant number of dislocations with 〈c〉 components were found in localized areas of the Be phase after extrusion. 相似文献
6.
《粉末冶金学》2013,56(3):440-444
AbstractEffects of the milling time, annealing temperature and vial rotation speed were investigated on the formation of MoSi2–CrSi2 nanocomposite powder. X-ray diffraction was used to characterise the milled and annealed powders. The morphological and microstructural evolutions were studied by scanning electron microscopy and transmission electron microscopy. Results showed that this composite formed after 20 h of milling with mechanically induced self-sustaining reaction mechanism at the cup speed of 640 rev min?1. On the other hand, this composite was partially synthesised after 50 h of milling with the gradual mode at the cup speed of 540 rev min?1. Low temperature polymorph of MoSi2 and CrSi2 were obtained after annealing at 1000°C at both speeds. The mean grain size <25 nm was procured for MoSi2–CrSi2 composite at both speeds on the basis of peak profile analysis and transmission electron microscopy. This composite maintained its nanocrystalline nature after annealing. 相似文献
7.
《粉末冶金学》2013,56(2):166-170
AbstractElemental tungsten powder was mechanically milled by planetary mill for 100 h. Particles were thinned down to nanometre scale. The shape of the milled powders was flat cylindrical with average diameter and length 12˙5 and 46˙5 nm respectively. The corresponding crystallite size obtained by X-ray diffraction (XRD) was 26˙96 nm. The results obtained by XRD and small angle X-ray scattering were well supported by transmission electron microscopy and high resolution transmission electron microscopy results. The maximum shrinkage of the compact has been observed at ~1500 K, which has been used as a guideline for sintering experiments. The powders sintered at 1773 K have resulted in 96% relative density. 相似文献
8.
This study investigated 1 wt.% Ni-CeO2 catalysts that were prepared using co-precipitation, deposition-precipitation, and impregnation methods for the reverse water-gas shift (RWGS) reaction. Characterizations of the catalyst samples were conducted by Brumauer-Emmett-Teller (BET), atomic absorption spectrophotometer (AAS), X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM) and temperature programmed reduction (TPR). The results showed that the Ni-CeO2 catalyst prepared using the co-precipitation method exhibited the best catalytic performance. In the Ni-CeO2 catalyst prepared using co-precipitation method, a combination of highly dispersed NiO and abundant oxygen vacancies was assumed to play a crucial role in determining the catalytic activity and selectivity of the RWGS reaction. 相似文献
9.
《粉末冶金学》2013,56(2):118-124
AbstractA detailed transmission electron microscopy study of the structure of aluminium nitride formed during sintering of powder injection moulded aluminium is presented. A polycrystalline layer formed on Al particle surfaces exposed to a nitrogen atmosphere. This layer consisted of fine, rod-like crystallites of hexagonal AlN typically aligned normal to the Al surface. A double layer of AlN separated by a thin layer of Al was observed at the interfaces between Al grains. In this report, the structure of the nitride is characterised and its influence on sintering is discussed. 相似文献
10.
《钢铁冶炼》2013,40(3):201-208
AbstractThe degree of supersaturation is a factor that influences the Al2O3 inclusion characteristics in steel. The influence of the addition of a large amount of Al in the molten steel on the formation, growth and morphology of Al2O3 inclusions was investigated by laboratory scale experiments. Consecutive steel samples were taken during the deoxidation process and subjected to chemical analysis (ICP-AES), automated image analysis (AIA) and scanning electron microscopy (SEM) assessment with respect to the extracted inclusions. The characterisation and quantification of Al2O3 particles show different growth processes, leading to variations in particle size distribution as well as in the morphology. 相似文献
11.
《粉末冶金学》2013,56(4):189-195
AbstractThe microstructures of rapidly solidified 7050 alloy powders have been observed by optical microscopy, scanning electron microscopy, and transmission electron microscopy and compared with those observed in a cast and homogenized ingot of the same material. The powder alloy was then consolidated by cold compaction followed by extrusion, the resulting structures being compared with those of extruded cast alloys. Finally, the structure and properties of the two materials were compared after heat treatment. It is shown that metastable phases not previously reported are present in the powder particles and that localized melting occurs in the powder alloy at a lower temperature than in the cast alloy; this is the primary cause of blistering, but appropriate modification to the heat treatment will prevent it occurring. Properties comparable to or better than the cast material may be produced by designing a more suitable heat treatment to avoid liquation of this metastable phase. The evidence presented suggests that the degassing procedure employed historically to counteract blistering is probably unnecessary. PM/0322 相似文献
12.
Microstructural characterization of self-propagating high-temperature synthesis/ dynamically compacted and hot-pressed titanium carbides 总被引:1,自引:0,他引:1
Kenneth S. Vecchio Jerry C. Lasalvia Marc A. Meyers George T. Gray 《Metallurgical and Materials Transactions A》1992,23(1):87-97
Titanium-Carbide produced by combustion synthesis followed by rapid densification in a high-speed forging machine was characterized
by optical microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). The density of the combustion synthesized/dynamically compacted TiC reached values greater than 96 pct of theoretical density,
based on TiC0.9, while commercially produced hot-pressed TiC typically exceeded 99 pct of theoretical density. The higher density of the
hot-pressed TiC was found to be attributable to a large volume fraction of heavy element containing inclusions. The microstructure
of both TiCs consists of equiaxed TiC grains with some porosity located both at grain boundaries and within the grain interiors.
In both cases, self-propagating high-temperature synthesis (SHS)/dynamically compacted (DC) and hot-pressed, the TiC is ordered
cubic (NaCl-structure,B
1; Space Group Fm3m) with a lattice parameter of ≈0.4310 nm, indicative of a slightly carbon deficient structure; stoichiometric
TiC has a lattice parameter of 0.4320 nm. For the most part, the grains were free of dislocations, although some dislocation
dipoles were found associated with the voids within the grain interiors. In one SHS/DC specimen, a new, complex Ti-Al-O(C)
phase was observed. The structure could not be matched with any previously published phases but is believed to be hexagonal,
with a c-axis/a-axis ratio of ≈6.6, similar to the AlCTi2 phase which has a point group 6 mmm. In all other SHS/DC TiC samples, the grains and grain boundaries were devoid of any
second-phase particles. The hot-pressed TiC exhibited a greater degree of porosity than the SHS/densified specimens and a
large concentration of second-phase particles at grain boundaries and within grains. The structure and composition of these
second-phase particles were determined by con-vergent beam electron diffraction (CBED) and X-ray microanalysis.
This paper is based on a presentation made in the symposium “Reaction Synthesis of Materials” presented during the TMS Annual
Meeting, New Orleans, LA, February 17–21, 1991, under the auspices of the TMS Powder Metallurgy Committee. 相似文献
13.
《中国稀土学报(英文版)》2020,38(2):148-156
Titanium dioxide nanoparticles modified with neodymium in the range of 1 mol% to 5 mol% were prepared with template-free sol-gel method.The structures of obtained samples were characterized by X-ray powder diffraction analysis.X-ray photoelectron spectroscopy,scanning electron microscopy,transmission electron microscopy and diffuse reflectance spectroscopy.The photocatalytic activity of the obtained samples was evaluated by photodegradation of methyl orange in aqueous solution under ultraviolet-visible(λ 350 nm) and visible(λ 420 nm) irradiation.The experimental results show that the 1 mol% Nd-doped TiO_2 exhibits the highest photocatalytic activity,of which the degradation can reach to 96.5% under visible irradiation.According to the XRD results,the pristine samples are combined with anatase TiO_2 and rutile TiO_2.while the Nd-doped TiO_2 samples are anatase TiO_2 only.This transformation has made an obvious promotion of photocatalyst activity after modification. 相似文献
14.
《粉末冶金学》2013,56(3):216-220
AbstractIn this study, nanocrystalline Ni0·64Zn0·36Fe2O4 powders were prepared using a planetary ball mill. The evolution of the microstructure and magnetic properties during the milling were studied by X-ray diffraction technique, scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometre. It is revealed from the results of the phase analysis that nanocrystalline Ni0·64Zn0·36Fe2O4 ferrite with average crystallite size of 6·18 nm and non-uniform lattice strain of 0·33% has been formed after 60 h of milling time. A progressive increase of saturation magnetisation and a dramatic decrease in coercivity were also observed with increasing milling time. 相似文献
15.
《粉末冶金学》2013,56(2):169-173
AbstractIn the present work, a powder mixture of pure WO3, graphite and Mg with a definite atomic ratio was milled at room temperature using a high energy ball mill method, and ball milled powders were analysed by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results indicated that after ball milling for a period of time, an oxidation–reduction reaction was successfully achieved among the Mg, graphite and WO3 powders to obtain MgO and WC. The extension of the ball milling led to the refinement of the powders. After ball milling 50 h, nanocrystalline WC grains (25 nm) were embedded into the fine matrix of MgO and formed fine nanocomposite MgO/WC powders (~100 nm in diameter). The experimental results and thermodynamic analysis showed that the formation of nanocomposite MgO/WC was a mechanically induced self-propagating reaction, and very short milling time was needed to complete the reaction. 相似文献
16.
《粉末冶金学》2013,56(3):223-227
AbstractThe present work reported the fabrication of the W–Cu nanocomposite precursor powders via high energy ball milling. The W–25 wt-%CuO powders were taken as the raw materials, and the following process condition was used: ball to powder weight ratio of 20 : 1, the rotation speed of 500 rev min&minus1, the milling time of 15–45 min and 1–40 h, and the mode of milling 10 min, air cooling 30 min. The phase and microstructure of the as milled powders with variation of milling time was investigated, using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The experiment results show that the nanocomposite powders can be successfully synthesised by mechanical alloying using a short time of 1 h. During the ball milling, CuO powders were reduced by W, and a portion of the W powders were oxidised into WOx (x=2 to 3). The possible mechanism of the reaction was detected. 相似文献
17.
《粉末冶金学》2013,56(1):37-42
AbstractIn this work elemental powders of Al and 2 wt-% graphite were mechanically alloyed in a high energy horizontal attritor under purified argon atmosphere for 0·5-2 h. Powder mixes were then cold pressed at 1200 MPa and sintered at 550°C for between 2-32 h under the same protective atmosphere. Structural evolution was characterised by X-ray diffraction, scanning electron microscopy and transmission electron microscopy techniques. Results revealed that mechanical alloying was very effective in pulverising the powder mix, where after 2 h, the mix was fine enough to oxidise rigorously when exposed to open air. In general however, mechanical alloying was found to be inefficient to synthesise Al with C. But after sintering, Al4C3 phase nanosized particles were formed in the microstructure. When the duration of sintering was prolonged, the particle population multiplied in number. Hence because of improvement in dispersion strengthening, the room temperature hardness of the material increased gradually. 相似文献
18.
B. I. Prenitzer L. A. Giannuzzi K. Newman S. R. Brown R. B. Irwin F. A. Stevie T. L. Shofner 《Metallurgical and Materials Transactions A》1998,29(9):2399-2406
Particles of Zn powder have been studied to show that high-quality scanning electron microscope (SEM) and transmission electron
microscope (TEM) specimens can be rapidly produced from a site-specific region on a chosen particle by the focused ion beam
(FIB) lift-out technique. A TEM specimen approximately 20-μm long by 5-μm wide was milled to electron transparency, extracted from the bulk particle, and micromanipulated onto a carbon coated copper
mesh TEM grid. Using the FIB lift-out method, we were able to prepare a site-specific TEM specimen from a difficult material
in under 3 hours. The TEM analysis of the lift-out specimen revealed a large amount of thin area free from characteristic
signs of damage that may be observed as a result of conventional argon ion milling. The overall microstructure of the specimen
prepared by the FIB lift-out method was consistent with samples prepared by conventional metallographic methods. A grain size
of ∼10 to 20 μm was observed in all specimens by both TEM and SEM analysis. Light optical microscopy revealed the presence of internal voids
in ∼10 to 20 pct of all particles. The SEM analysis showed the voids to extend over ∼70 pct of the particle volume in some
cases. 相似文献
19.
《粉末冶金学》2013,56(2):140-145
AbstractAl matrix composites reinforced by Al–Cu–Fe quasicrystalline (QC) phase particles were produced from a mixture of Al and QC powders using electrical current heating and conventional sintering. A combination of X-ray diffractrometry, transmission and scanning electron microscopy was used to characterise the microstructure of consolidated specimens. The metallic bonding of the Al matrix and particles was improved by higher temperature sintering or electrical current heating. However, the dissolution of QC particles into the Al matrix was inevitable during heating and resulted in the formation of ω and/or β phases. The dissolution of QC particles was effectively reduced using prealloyed Al powder containing 2 at.-%Cu. This had led to an increase in microhardness from 96 to 139 HV for specimens using pure Al to prealloyed Al powders. A homogeneous distribution of QC particles within the Al matrix could be achieved by mechanical milling followed by consolidation. 相似文献
20.
D. Del Genovese J. Rösler P. Strunz D. Mukherji R. Gilles 《Metallurgical and Materials Transactions A》2005,36(12):3439-3450
The new Ni-Fe-based superalloy DT706, derived from INCONEL 706, is the object of studies for potential uses in turbine-disk
applications at temperatures above 973 K. This alloy aims at improving the microstructural stability while preserving the
excellent machinability and good mechanical properties of the base material. This article is the first of a two-part study
concentrating on the characterization of the microstructure of the DT706 precipitates, depending on the heat-treatment conditions.
Analyses were performed by means of ex-situ small-angle neutron scattering (SANS) measurements, together with conventional scanning electron microscopy (SEM) and transmission
electron microscopy (TEM) microscopy, on experimentally-heat-treated samples. The results, when compared to a similar analysis
previously made on INCONEL 706, showed that the precipitation characteristics of DT706 reflect compositional changes, but
are still remarkably dependent on the cooling stages between the different heat-treatment steps. 相似文献