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1.
In previous studies, it has been demonstrated that nanostructured Al2O3-13 wt.%TiO2 coatings deposited via air plasma spray (APS) exhibit higher wear resistance when compared to that of conventional coatings.
This study aimed to verify if high-velocity oxy-fuel (HVOF)-sprayed Al2O3-13 wt.%TiO2 coatings produced using hybrid (nano + submicron) powders could improve even further the already recognized good wear properties
of the APS nanostructured coatings. According to the abrasion test results (ASTM G 64), there was an improvement in wear performance
by a factor of 8 for the HVOF-sprayed hybrid coating as compared to the best performing APS conventional coating. When comparing
both hybrid and conventional HVOF-sprayed coatings, there was an improvement in wear performance by a factor of 4 when using
the hybrid material. The results show a significant antiwear improvement provided by the hybrid material. Scanning electron
microscopy (SEM) at low/high magnifications showed the distinctive microstructure of the HVOF-sprayed hybrid coating, which
helps to explain its excellent wear performance.
This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been
expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain
Montavon, Ed., ASM International, Materials Park, OH, 2007. 相似文献
2.
Air plasma-sprayed conventional alumina-titania (Al2O3-13wt.%TiO2) coatings have been used for many years in the thermal spray industry for antiwear applications, mainly in the paper, printing,
and textile industries. This work proposes an alternative to the traditional air plasma spraying of conventional aluminatitania
by high-velocity oxyfuel (HVOF) spraying of nanostructured titania (TiO2). The microstructure, porosity, hardness (HV 300 g), crack propagation resistance, abrasion behavior (ASTM G65), and wear
scar characteristics of these two types of coatings were analyzed and compared. The HVOF-sprayed nanostructured titania coating
is nearly pore-free and exhibits higher wear resistance when compared with the air plasma-sprayed conventional alumina-titania
coating. The nanozones in the nanostructured coating act as crack arresters, enhancing its toughness. By comparing the wear
scar of both coatings (via SEM, stereoscope microscopy, and roughness measurements), it is observed that the wear scar of
the HVOF-sprayed nanostructured titania is very smooth, indicating plastic deformation characteristics, whereas the wear scar
of the air plasma-sprayed alumina-titania coating is very rough and fractured. This is considered to be an indication of a
superior machinability of the nanostructured coating. 相似文献
3.
Nanostructured Bi2Se3 and Sn0.5-Bi2Se3 were successfully synthesized by hydrothermal coreduction from SnCl2·H2O and the oxides of Bi and Se. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy
(TEM), and field emission scanning electron microscope (FESEM). Bi2Se3 powders obtained at 180°C and 150°C consist of hexagonal flakes of 50–150 nm in side length and nanorods of 30–100 nm in
diameter and more than 1 μm in length. The product obtained at 120°C is composed of thin irregular nanosheets with a size
of 100–200 nm and several nanometers in thickness. The major phase of Sn0.5-Bi2Se3 synthesized at 180°C is similar to that of Bi2Se3. Sn0.5-Bi2Se3 powders are primarily nanorod structures, but small amount of powders demonstrate irregular morphologies. 相似文献
4.
Tabbetha A. Dobbins Richard Knight Merrilea J. Mayo 《Journal of Thermal Spray Technology》2003,12(2):214-225
High velocity oxy-fuel (HVOF) thermal spray has been successfully used to deposit yttria-stabilized zirconia (YSZ) for thermal
barrier coating (TBC) applications. Adherent coatings were obtained within a limited range of spray conditions using hydrogen
as fuel gas. Spray parameters such as hydrogen-to-oxygen ratio, spray distance, and substrate cooling were investigated. Spray
distance was found to have a pronounced effect on coating quality; adherent coatings were obtained for spray distances between
75 and 125 mm from the gun exit for the hydrogen-to-oxygen ratios explored. Compared to air plasma spray (APS) deposited YSZ
coatings, the HVOF deposited coatings were more fully stabilized in the tetragonal phase, and of similar density, surface
roughness, and cross-sectional microhardness. Notably, fracture surfaces of the HVOF coatings revealed a more homogeneous
structure. Many theoretical models predict that it should not be possible to melt YSZ in an HVOF flame, and therefore it should
not be possible to deposit viable YSZ coatings by this process. The experimental results in the present work clearly contradict
those expectations. The present results can be explained by taking into account the effect of partial melting and sintering
on particle cohesion, as follows. Combustion chamber pressures (P
o) of ∼3.9 bar (58.8 psi) realized during HVOF gun operation allows adiabatic flame temperature values that are above the zirconia
melting temperature. Under these conditions, the Ranz-Marshall heat transfer model predicts HVOF sprayed particle surface
temperatures T
p that are high enough for partial melting of small (∼10 μm) zirconia particles, T
p=(1.10−0.95)T
m. Further analysis shows that for larger particles (38 μm), adherent coatings are produced when the particle temperature,
T
p=0.59−0.60 T
m, suggesting that sintering may have a role in zirconia particle deposition during HVOF spray. These results suggest two different
bonding mechanisms for powders having a broad particle size distribution. 相似文献
5.
Yunjian Liu Xinhai Li Huajun Guo Zhixing Wang Qiyang Hu Wenjie Peng Yong Yang 《稀有金属(英文版)》2009,28(4):322-327
Spinel LiMn2O4 was synthesized by a solid-state method. A 204468-size battery was fabricated and stored at 55°C. The structure and morphology
of the LiMn2O4 cathode were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) technique. Energy dispersive spectroscopy
(EDS) was used to analyze the surface component of the carbon anode. The discharge capacities of LiMn2O4 stored for 0, 24, 48, and 96 h are 106, 98, 96, and 92 mAh·g−1, respectively. The cyclic performance is improved after storage. The capacity retentions of LiMn2O4 stored for 0, 24, 48, and 96 h are 83.8%, 85.8%, 86.9%, and 88.6% after 180 cycles. The intensity of all the LiMn2O4 diffraction peaks is weakened. Mn is detected from the carbon electrode when the battery is stored for 96 h. Cyclic voltammograms
and electrochemical impedance spectroscopy (EIS) were used to examine the surface state of the electrode after storage. The
results show that the resistance and polarization of LiMn2O4/electrolyte is increased after storage, which is responsible for the fading of capacity. 相似文献
6.
Al2O3/ZrO2/Al2O3 gate stacks were prepared on ultrathin SOI (Silicon on insulator) substrates by ultrahigh vacuum electron beam evaporation
and post-annealed in N2 at 450°C for 30 min. Three clear nanolaminate layered structure of Al2O3(2.1 nm)/ZrO2(3.5 nm)/Al2O3(2.3 nm) was observed with a high-resolution cross-sectional transmission electron microscope (HR-XTEM). High frequency capacitance
voltage (C-V) characteristics of a fully depleted (FD) SOI MOS capacitor at 1 and 5 MHz were studied. The minority carriers
determine the high frequency C-V properties, which is opposite to the case of bulk MOS capacitors. The series resistance of
the SOI substrate is found to be the determinant factor of the high frequency characteristics of FD SOI MOS capacitors.
This article is based on a presentation in “The 7th Korea-China Workshop on Advanced Materials” organized by the Korea-China
Advanced Materials Cooperation Center and the China-Korea Advanced Materials Cooperation Center, held at Ramada Plaza Jeju
Hotel, Jeju Island, Korea on August 24≈27, 2003. 相似文献
7.
S. M. A. Hosseini M. Mousavi M. Amiri 《Protection of Metals and Physical Chemistry of Surfaces》2009,45(4):461-465
This investigation deals with corrosion behavior of high strength titanium alloy in concentrated sulphuric acid solution containing
different concentrations (500, 1000, 1500 ppm) of fluoride ion (F−) using various organic compounds (MPA, L-OH, NFP) as inhibitor, potentiodynamically. The open circuit potential values noted
before and after each experiment, varied appreciably. These values were negative before polarization but after completion
of the experiment turned positive and remained stable over long period of time. It is observed that cathodic current density
values increase with increasing cathodic potential (more negative) and fluoride ion. The values of cathodic Tafel slopes derived
from the curves (∼110 − 140 mV/dec I) indicate hydrogen evolution reaction (h.e.r). The corrosion potential (E
corr) varied slightly with addition of inhibitors. The corrosion current densities (I
corr) increased with increasing fluoride ion concentration, but these values decreased appreciably when inhibitor (MPA) was used.
SEM micrograph reveals reduction of pits in the presence of inhibitor (MPA). So this concludes that organic compound was used
in this case acts as a good inhibitor.
The article is published in the original. 相似文献
8.
Lutz-Michael Berger Sabine Saaro Tobias Naumann Michaela Kašparova František Zahálka 《Journal of Thermal Spray Technology》2008,17(3):395-403
The composition WC-(W,Cr)2C-Ni is one of the standard compositions used for the preparation of thermally sprayed coatings by high velocity oxy-fuel
(HVOF) spraying. Surprisingly, this composition has been poorly investigated in the past. Frequent use of commercial designations
WC-‘CrC’-Ni, WC-Cr3C2-Ni, and WC-NiCr indicates the insufficient knowledge about the phase compositions of these powders and coatings. The properties
of these coatings differ significantly from those of WC-Co and WC-CoCr coatings. In this paper, the results of different series
of experiments conducted on HVOF-sprayed WC-(W,Cr)2C-Ni coatings are compiled and their specific benefits pointed out. The focus of this study is on the analysis of the microstructures
and phase compositions of the feedstock powders and coatings. Unlike WC-Co and Cr3C2-NiCr, WC-(W,Cr)2C-Ni is not a simple binary hard phase—binder metal composite. The phase (W,Cr)2C with unknown physical and mechanical properties appears as a second hard phase, which is inhomogeneously distributed in
the feedstock powders and coatings. As examples of coating properties, the oxidation resistance and dry sliding wear properties
are compared with those of WC-10%Co-4%Cr coatings. 相似文献
9.
A nano-sized Co3O4 powder was prepared using a spray conversion method that could be applied for mass production. The spray-conversion process
consisted of spray drying of a metallic liquid solution, a calcination treatment, and a ball milling process. The calcined
Co3O4 powder consisted of agglomerated spherical clusters with nano-sized particles. After milling for 24 h, agglomerated powders
were fragmented into fine powders sized below 60 nm. The lithium/cobalt oxide cell was charge-discharged at a constant current
density of 0.2 mAcm−2 and showed a first discharge capacity of 1100 mAhg−1. The discharge capacity of the Li/Co3O4 cell drastically decreased with cycle number. By increasing the carbon content of the anode, the cycle life was improved.
For a Co3O4 electrode containing 40 wt.% carbon, the discharge capacity was over 400 mAhg−1 after 50 cycles. The spray conversion method might be a useful method to prepare nano-sized Co3O4 powder for the anode material of lithium batteries. 相似文献
10.
Terence P. Savas Allen Yi-Lan Wang James C. Earthman 《Journal of Materials Engineering and Performance》2003,12(2):165-171
The effect of heat treatment on the corrosion resistance of 440C stainless steel was investigated in a 20% HNO3 + 2.5% Na2Cr2O7 solution using electrochemical noise (ECN) measurements, electrochemical impedance spectroscopy (EIS), and scanning electron
microscopy (SEM) examinations. The noise resistance (Rn), which has been found to be inversely related to the localized corrosion rate, was measured to be 5.7E + 08 Ω-cm2, 4.2E + 08 Ω-cm2, and 3.7E + 04 Ω-cm2 for the oil-quenched, air-quenched, and vacuum furnace cooled (VFC) samples, respectively, after 1200 s exposures. The Rn for all heat treat conditions stabilized within a range of 1.0E + 07 Ω-cm2 to 3.2E + 08 Ω-cm2 after 2 h exposures. The EIS response showed a polarization resistance (R
p) on the order of 6.6E + 04 Ω-cm2, 5.3E + 04 Ω-cm2, and 1.1E + 04 Ω-cm2 for the oil-quenched, air-quenched, and VFC samples, respectively, after 2 h exposures. The EIS data are in good agreement
with ECN data and indicate that after longer exposures, general corrosion mechanisms dominate and the corrosion rates are
comparable. SEM examinations of specimens subjected to 1200 s exposures revealed that severity of pitting and intergranular
corrosion damage was consistent with trends in the Rn data. Specifically, the electrochemical noise data as well as SEM examinations of specimens revealed a higher localized
corrosion resistance of the hardened specimens during the early stages of passivation. This greater resistance to localized
corrosion can be attributed to an increased stability of the natural passive film resulting from a higher concentration of
chromium atoms in solution for the martensite phase. 相似文献
11.
Ch.Alk. Apostolopoulos D. Michalopoulos 《Journal of Materials Engineering and Performance》2007,16(1):63-67
The impact of corrosion on the properties of steel reinforcement in concrete structures was examined. An experimental investigation
was carried out in order to gain better insight of the effect of corrosion on the mass loss, fatigue and hardness, of BSt500
s
12 and 8 mm diameter steel bars that were artificially corroded in a Sodium Chloride environment for different corrosion
levels. The fatigue limit of the 12 mm steel was reduced by 20–40% and the mass loss was 1.5–2.9% for 15 and 30 days corrosion
level, while the mass loss of the 8 mm steel was 1.2–32% for 10–90 days corrosion. The hardness of the 8 mm steel was reduced
by 25–35% and 2–10% in the outer and inner layers of the specimens for 30 and 60 days corrosion respectively. Corrosion created
considerable reduction in the fatigue strength and life of the steel bars due to drastic drop in the energy density, formation
of pitting and notches along with destruction of the hardest outer layer of martensite. 相似文献
12.
N. Garimella M. Ode M. Ikeda H. Murakami Y. H. Sohn 《Journal of Phase Equilibria and Diffusion》2009,30(3):246-253
Ternary interdiffusion in L12-Ni3Al with ternary alloying addition of Re was investigated at 1473 K using solid-to-solid diffusion couples. Interdiffusion
flux of Ni, Al, and Re were directly calculated from experimental concentration profiles and integrated for the determination
of average ternary interdiffusion coefficients. The magnitude of main interdiffusion coefficients and was determined to be much larger than that of the main interdiffusion coefficient A moderate tendency for Re to substitute for Al sites was reflected by its influence on interdiffusion of Al, quantified
by large and positive coefficients. Similar trends were observed from ternary interdiffusion coefficients determined by Boltzmann-Matano analysis.
Profiles of concentrations and interdiffusion fluxes were also examined to estimate binary interdiffusion coefficients in
Ni3Al, and tracer diffusion coefficients of Re (5.4 × 10−16 ± 2.3 × 10−16 m2/s) in Ni3Al. 相似文献
13.
Metal-insulator-semiconductor (MIS) structures containing Ge nanocrystals embedded in both Al2O3 and ZrO2/Al2O3 are fabricated by an ultra-high vacuum electron-beam evaporation method. Secondary ion mass spectroscopy (SIMS) results indicate
that Ge embedded in Al2O3 diffuses towards the surface of the Al2O3 layer after annealing at 800°C in N2 ambient for 30 min. Ge embedded in ZrO2/Al2O3 is stable, thus inducing less leakage current. Capacitance voltage studies indicate that annealing can effectively passivate
the negatively charged trapping centers. Memory effect of the Ge nanoclusters is verified by hysteresis in the C-V curves
in the Al2O3/Ge+Al2O3/Al2O3 and ZrO2/Ge+Al2O3/Al2O3 samples.
This article is based on a presentation in “The 7th Korea-China Workshop On Advanced Materials” organized by the Korea-China
Advanced Materials Cooperation Center and the China-Korea Advanced Materials Cooperation Center, held at Ramada Plaza Jeju
Hotel, Jeju Island, Korea on August 24–27, 2003. 相似文献
14.
A new LiCoO2 recovery technology for Li-ion batteries was studied in this paper. LiCoO2 was peeled from the Al foil with dimethyl acetamide (DMAC), and then polyvinylidene fluoride (PVDF) and carbon powders in
the active material were eliminated by high temperature calcining. Subsequently, Li2CO3, LiOH·H2O and LiAc·2H2O were added into the recycled powders to adjust the Li/Co molar ratio to 1.00. The new LiCoO2 was obtained by calcining the mixture at 850°C for 12 h in air. The structure and morphology of the recycled powders and
resulting samples were studied by XRD and SEM techniques, respectively. The layered structure of LiCoO2 synthesized by adding Li2CO3 is the best, and it is found to have the best characteristics as a cathode material in terms of charge-discharge capacity
and cycling performance. The first discharge capacity is 160 mAh·g−1 between 3.0–4.3 V. The discharge capacity after cycling for 50 times is still 145.2 mAh·g−1. 相似文献
15.
Insup Lee 《Metals and Materials International》2008,14(1):77-81
Plasma nitrocarburizing and post-oxidation treatments were performed to improve the wear and corrosion resistance of S45C
steel. Plasma nitrocarburizing was conducted for 3 h at 570°C in a nitrogen, hydrogen and methane atmosphere to produce the
ε-Fe2−3(N,C) phase. It was found that the compound layer produced by plasma nitrocarburising was predominantly composed of the ∈-phase
with traces of the γ′-Fe4(N,C) phase. The thickness of the compound layer was approximately 12 μm and the diffusion layer was approximately 300 μm
in thickness. Plasma post oxidation was performed on nitrocarburized samples with various oxygen/hydrogen ratios at a constant
temperature of 500°C for 1 h. The very thin magnetite (Fe3O4) layer 1 μm to 2 μm in thickness on top of the compound layer was obtained by plasma post oxidation. It was also confirmed
that further improvement of the corrosion characteristics of the nitrocarburized compound layer was possible with an application
of the superficial magnetite layer. Finally, throttle valve shafts of S45C steel were treated under optimum plasma processing
conditions. Accelerated life time test results using a throttle body assembled with a shaft treated by plasma nitrocarburising
and post oxidation showed that plasma nitrocarburizing and plasma post-oxidation processes could be a viable technology in
the very near future in place of Cr6 plating. 相似文献
16.
Electric transport and magnetoresistance characteristics were investigated for Fe3O4-x Fe(x=0, 10, 20 wt.%) samples and Fe3O4-α-Fe2O3 samples sintered at 500°C. For composition dependence of Fe3O4-x Fe samples, the largest room temperature MR, 3.3% at 10 kOe, was obtained from a Fe3O4-10 Fe sample. For the surface heat treatment dependence of Fe3O4 powders, the largest room temperature MR, 4% at 10 kOe, was obtained from a Fe3O4-α-Fe2O3 sample sintered with Fe3O4 powders heated at 200°C in air. It was found that these enhanced MR ratios always appear together with the appropriate excess
resistance which is regarded as the tunneling barrier. These enhanced MR ratios of Fe3O4-10 Fe and Fe3O4-α-Fe2O3 samples can be explained by the increased interparticle contact sites and the appropriate thickness of α-Fe2O3, respectively. 相似文献
17.
The Na2O-B2O3 system is thermodynamically optimized by means of the CALPHAD method. A two-sublattice ionic solution model, (Na+1)P(O−2,BO3
−3,B4O7
−2,B3O4.5)Q, has been used to describe the liquid phase. All the solid phases were treated as stoichiometric compounds. A set of thermodynamic
parameters, which can reproduce most experimental data of both phase diagram and thermodynamic properties, was obtained. Comparisons
between the calculated results and experimental data are presented. 相似文献
18.
The photoelectrochemical characteristics of plasma-sprayed porous TiO2, TiO2-5%ZnO, and TiO2-10%ZnO electrodes in 0.1 N NaOH solution were studied through a three-electrode cell system. The microstructure, morphology,
and composition of the electrodes were analyzed using an electron probe surface roughness analyzer (ERA-8800FE), scanning
electron microscopy, and x-ray diffraction. The results indicate that the sprayed electrodes have a porous microstructure,
which is affected by the plasma spray parameters and composition of the powders. The TiO2-ZnO electrodes consist of anatase TiO2, rutile TiO2, and Zn2Ti3O8 phase. The photoresponse characteristics of the plasma-sprayed electrodes are comparable to those of single-crystal TiO2, but the breakdown voltage is close to 0.5 V (versus that of a saturated calomel electrode). The short-circuit photocurrent
density (J
SC) increases with a decrease of donor concentration, which was calculated according to the Gartner-Butler model. For the lowest
donor concentration of a TiO2-5%ZnO electrode sprayed under an arc current of 600 A, the short-circuit J
SC is approximately 0.4 mA/cm2 higher than that of the TiO2 electrodes under 30 mW/cm2 xenon light irradiation. The J
SC increases linearly with light intensity.
The original version of this paper was published as part of the DVS Proceedings: “Thermal Spray Solutions: Advances in Technology
and Application,” International Thermal Spray Conference, Osaka, Japan, 10–12 May 2004, CD-Rom, DVS-Verlag GmbH, Düsseldorf,
Germany. 相似文献
19.
Chang Suk Han 《Metals and Materials International》2007,13(1):31-37
Transmission electron microscope investigation has been performed on the particle-dislocation interactions in Ni3Al-based intermetallics containing various types of fine precipitates. In an Ll2-ordered Ni3Al alloy with 4 mol.% of chromium and 0.2–0.5 mol.% of carbon, fine octahedral precipitates of M23C6 type carbide, which has a cube-cube orientation relationship with the matrix, appear during aging. Typical Orowan loops are
formed in Ni3Al containing fine dispersions of M23C6 particles. In the alloys with appropriate titanium content, fine precipitates of coherent disordered γ are formed during
aging. The γ precipitates are initially spherical or rounded cubic in shape and grow into platelets as aging proceeds. Loss
of coherency is initiated by the introduction of dislocations at the γ/γ′ interface and results in step formation at the dislocations.
The γ precipitates become globular after the loss of coherency. In the γ′ phase hardened by the precipitation of the disordered
γ phase, dislocations are attracted into the disordered γ phase and cut through the particles during deformation at any stage
of aging. In Ni3Al containing a fine dispersion of disordered γ, superdislocations are strongly attracted to the disordered particles and
dissociate on the (111) plane in the γ particles, while they dissociate on the (010) plane in the matrix. It is shown by comparison
that the strengthening due to attractive interaction is more effective than that due to repulsive interaction. The roles of
the variation of the interaction modes and of the dissociation of superdislocations in the matrix and particles are discussed
in connection with the optimum microstructures of Ll2-ordered intermetallics as high temperature structural materials. 相似文献
20.
Nanostructured skutterudite-related compound Fe0.25Ni0.25Co0.5Sb3 was synthesized by a solvothermal method using FeCl3, NiCl2, CoCl2, and SbCl3 as the precursors and NaBH4 as the reductant. The solvothermally synthesized powders consisted of fine granules with an average particle size of tens
of nanometers. The bulk material was prepared by hot pressing the powders. Transport property measurements indicated a heavily
doped semiconductor behavior with n-type conduction. The thermal conductivity is about 1.83 W·m−1·K−1 at room temperature and decreases to 1.57 W·m−1·K−1 at 673 K. The low thermal conductivity is attributed to small grain size and high porosity. A maximum dimensionless figure
of merit of 0.15 is obtained at 673 K. 相似文献