共查询到20条相似文献,搜索用时 31 毫秒
1.
B. Shri Prakash N. Balaji V. K. William Grips Siju S. T. Aruna 《Journal of Thermal Spray Technology》2012,21(6):1300-1308
Plasma-sprayed coatings of 8 mol% yttria-stabilized zirconia (YSZ) were fabricated using the feedstock powders obtained from co-precipitation (PPT) and spray-drying (SD) processes. Particle size and the specific mass (SM) of the feedstock powder were found to be the critical parameters that influence the microstructural and electrical properties of the coatings. While dense and larger particle-sized PPT powder resulted in a porous microstructure, dense coatings were obtained for SD powders with relatively lower SM. Electrical conductivity values of SD-coatings were found to be 30% higher than that of PPT-coatings. Electrical conductivity values of plasma-sprayed PPT-coatings improved significantly on decreasing the particles size. However, the size effect was only subtle in the case of SD coatings. PPT-coatings fabricated from smaller particle-sized powders had the necessary electrical conductivities appropriate for solid oxide fuel cell electrolyte applications. 相似文献
2.
Tribological properties of TiC-Fe coatings obtained by plasma spraying reactive powders 总被引:1,自引:0,他引:1
Titanium carbide-based coatings have been considered for use in sliding wear resistance applications. Carbides embedded in
a metal matrix would improve wear properties, providing a noncontinuous ceramic surface. TiC-Fe coatings obtained by plasma
spraying of spray-dried TiC-Fe composite powders containing large and angular TiC particles are not expected to be as resistant
as those containing TiC particles formed upon spraying. Coatings containing 60 vol% TiC dispersed in a steel matrix deposited
by plasma spraying reactive micropellets, sintered reactive micropellets, and spray-dried TiC-Fe composite powders are compared.
The sliding wear resistance of these coatings against steel was measured following the test procedure recommended by the Versailles
Advanced Materials and Standards (VAMAS) program, and the inherent surface porosity was evaluated by image analysis. Results
show that, after a 1-km sliding distance, TiC-Fe coatings obtained after spraying sintered reactive powders exhibit scar ring
three times less deep than sprayed coatings using spray-dried TiC-Fe composite powders. For all coatings considered, porosity
is detrimental to wear performance, because it generally lowers the coating strength and provides cavities that favor the
adhesion of metal. However, porosity can have a beneficial effect by entrapping debris, thus reducing friction. The good wear
behavior of TiC-Fe coatings manufactured by plasma spraying of sintered reactive powders is related to their low coefficient
of friction against steel. This is due to the microstructure of these coatings, which consists of 0.3 to 1 μm TiC rounded
particles embedded in a steel matrix.
Presented at the International Conference on Metallurgical Coatings and Thin Films, ICMCTF-92, Apr 6–10, 1992, San Diego. 相似文献
3.
R. Vaßen D. Hathiramani J. Mertens V.A.C. Haanappel I.C. Vinke 《Surface & coatings technology》2007,202(3):499-508
The potential of atmospheric plasma spraying (APS) technology has been investigated for the manufacture of anode, electrolyte and cathode of a solid oxide fuel cell. As the substrate a tape-casted FeCr alloy was used. It turned out that all layers can be applied by this technique, however, the APS cathode layer, although applied by suspension plasma spraying led to cells with rather low performance. Much better cell characteristics could be obtained by using screen-printed LSCF cathodes, which do not need any additional thermal treatment.Anode layers with high electrochemical activity were produced by separate injection of NiO and YSZ powders. The manufacturing of gastight electrolyte layers was a key-issue of the present development. As APS ceramic coatings typically contain microcracks and pores their leakage rate is not sufficiently low for SOFC applications.Based on the understanding of the formation of defects during spraying an optimized spraying process was developed which led to highly dense coatings with the appearance of a bulk, sintered ceramic. Open cell voltages above 1 V proofed the low leakage rates of the rather thin (< 50 μm) coatings. With these cells having a screen-printed cathode an output power of 500 mW/cm2 could be achieved at 800 °C.It turned out that the long-term stability of the metal substrate based APS SOFCs was rather poor. The aging of the cells was probably due to interdiffusion of anode and substrate material. Hence, diffusion barrier was applied by APS between substrate and anode. These layers were very effective in reducing the degradation rate. For these cells the output power reached 800 mW/cm2. 相似文献
4.
This article reports the effects of hot isostatic pressing (HIPing) on the microstructure and properties of plasma sprayed
Ni-based alloy coatings. Hot isostatic pressing was used as a post- spray treatment on plasma sprayed Ni-5Al, Ni-20Al, and
NiCrAl coatings. The aim was to densify the coatings and modify physical properties such as strength, amount of porosity,
and hardness. The coatings were HIPed at 750 to 950 ‡C at pressures of 50 to 200 MPa and held for 1 h. The treated coatings
were examined by optical microscopy and scanning electron microscopy (SEM). Coating porosity was determined using a combination
of an image analyzer and SEM. Near- zero porosity levels could be obtained, and HIP treatment at increasing temperatures and
pressures changed the microstructure and increased the microhardness of the coatings. Mechanical testing of the coatings was
performed on a Dynamic Mechanical Analyzer (DMA) from ambient to — 1000 ‡C. The results showed that the elastic modulus of
HIPed coatings was greater than as-sprayed coatings up to — 750 ‡C. These changes can be related to plastic flow, interlamellar
diffusion, and creep that occur at increased temperatures and pressures. 相似文献
5.
Electrotribological applications require materials with both high electrical conductivity and wear resisance. For this purpose,
a copper- base plasma sprayed coating containing titanium diboride particles was developed. The process for fabricating this
CU- TiB2 coating consists of plasma spraying reactive powders that contain a Cu- Ti alloy and boron. The reaction between the copper
alloy and boron proceeds in different steps going from solid- state diffusion of titanium and copper to the synthesis of TiB2 in a liquid below 1083 ‡C. Plasma sprayed copper coatings contain finer TiB2 crystals than Cu- TiB2 materials synthesized in a furnace at 1200 ‡C. Coatings with 25 vol% TiB2 have hardnesses that are comparable to Cu- Co-
Be and Cu- Ni- Be alloys and to Cu- W and Cu- Mo alloys used in spot welding. Their low electrical resistivity of 52 ΜΩ cm
could be increased by lowering the oxygen content with coatings and controlling the formation of TiB2 clusters, the titanium content in solution in copper remaining low after the synthesis reaction. 相似文献
6.
Yanchun Dong Dianran Yan Jining He Xiangzhi Li Jianxin Zhang 《Journal of Thermal Spray Technology》2006,15(3):323-328
Ceramic-metal composite (CMC) coatings were deposited on the surface of Fe-0.14–0.22 wt.% C steel by plasma spraying of self-reacting
Fe2O3−Al composite powders. The dry sliding friction and wear character of the CMC coatings are investigated in this paper. The
wear resistance of the CMC coatings was significantly better than that of Al2O3 coatings under the same sliding wear conditions. The tough metal, which is dispersed in the ceramic matrix, obviously improved
the toughness of the CMC coatings. Wear mechanisms of the CMC coatings were identified as a combination of abrasive and adhesive
wear. 相似文献
7.
T. Varis J. Knuuttila E. Turunen J. Leivo J. Silvonen M. Oksa 《Journal of Thermal Spray Technology》2007,16(4):524-532
The potential of the high-velocity oxy-fuel (HVOF) thermal spray process for reduced porosity in coatings compared to those
produced by other ambient thermal spray processes is well known. The ability to produce high-density ceramic coatings offers
potential in high-performance applications in the field of wear, corrosion resistance, and dielectric coatings. However, due
to operational limit of the HVOF process to effectively melt the ceramic particles, the process—structure relationship must
be well optimized. It has been also demonstrated that benefits from HVOF ceramic coatings can be obtained only if particles
are melted enough and good lamella adhesion is produced. One strategy to improve melting of ceramic particles in relative
low-flame temperatures of HVOF process is to modify particle crystal structure and composition. In this paper the effect of
the powder manufacturing method and the composition on deposition efficiency of spray process as well as on the mechanical
properties of the HVOF sprayed are studied. Effect of fuel gas, hydrogen vs. propane, was also demonstrated. Studied materials
were alumina-, chromia-, and titania-based agglomerated powders. Coating properties such as microstructure, hardness, abrasive
wear resistance, and relative fracture toughness were compared to the coating manufactured by using conventional fused and
crushed powders. It can be concluded that powder size distribution and microstructure should be optimized to fulfill process
requirements very carefully to produce coatings with high deposition efficiency, dense structure, improved fracture toughness,
and adhesion. 相似文献
8.
The effects of artificial aging on the microstructure and fracture toughness of Al-Cu-Li alloy 2195 总被引:2,自引:0,他引:2
P. S. Chen A. K. Kuruvilla T. W. Malone W. P. Stanton 《Journal of Materials Engineering and Performance》1998,7(5):682-690
Aluminum-lithium alloys have shown promise for aerospace applications, and National Aeronautics and Space Administration (NASA)
has selected the aluminum-lithium Alloy 2195 for the main structural alloy of the super light weight tank (SLWT) for the space
shuttle. This alloy has significantly higher strength than conventional2xxx alloys (such as 2219) at both ambient and cryogenic temperatures. If properly processed and heat treated, this alloy can
display higher fracture toughness at cryogenic temperature than at ambient temperature. However, the properties of production
materials have shown greater variation than those of other established alloys, as is the case with any new alloy that is being
transitioned to a demanding application.
Recently, some commercial 2195 plates for the SLWT program were rejected, mostly due to low CFT or FTR at ambient and cryogenic
temperatures. Investigation of the microstructure property relationships of Al-Cu-Li based alloys indicates that the poor
fracture toughness properties can be attributed to excessive T1 precipitation at subgrain boundaries. Lowering the aging temperature is one way to avoid excessive T1 precipitation at subgrain boundaries. However, this approach results in a significant drop in yield strength. In addition,
low-temperature aging is associated with sluggish aging kinetics, which are not desirable for industrial mass production.
Therefore, the present study was undertaken to develop an aging process that can improve fracture toughness without sacrificing
yield and tensile strength.
A multistep heating-rate controlled (MSRC) aging treatment has been developed that can improve the cryogenic fracture toughness
of aluminum-lithium Alloy 2195. At the same levels of yield strength (YS), this treatment results in considerably higher fracture
toughness than that found in Alloy 2195, which has received conventional (isothermal) aging. Transmission electron microscopy
revealed that the new treatment greatly reduces the size and density of subgrain-boundary T1 precipitates. In addition, it promotes T1 and θ" nucleation, resulting in a fine and dense distribution of precipitate particles in the matrix. The MSRC aging treatment
consists of (a) aging at 127‡C (260‡F) for 5 h, (b) heating continuously from 127‡C (260‡F) to 135‡C (275‡F) at a rate of
0.556‡C/h (1‡F/h), (c) holding at 135‡C (275‡F) for 5 h, (d) heating continuously from 135 to 143‡C (275 to 290‡F) at a rate
of 0.556‡C/h (1‡F/h), and (e) holding at 143‡C (290‡F) for 25 h to obtain a near peak-aged condition. 相似文献
9.
Influence of the ceramic particle size on the process of formation of cermet coatings by cold spray is experimentally studied.
A specially developed nozzle with separate injection of ceramic and metal powders into the gas stream is used in the experiments.
The results obtained demonstrate that fine ceramic powders (Al2O3, SiC) produce a strong activation effect on the process of spraying soft metal (Al, Cu) and increase deposition efficiency
of the metal component of the mixture compared to the pure metal spraying. At the same time, coarse ceramic powder produces
a strong erosion effect that considerably reduces coating mass growth and deposition efficiency of the metal component. It
is experimentally shown that the addition of fine hard powder to soft metals as Al and Cu allows to significantly reduce the
“critical” temperature (the minimum gas stagnation temperature at which a nonzero particle deposition is observed) for spraying
these metals. 相似文献
10.
Hamidreza Salimijazi Mehdi Hosseini Javad Mostaghimi Larry Pershin Thomas W. Coyle Hamed Samadi Ali Shafyei 《Journal of Thermal Spray Technology》2012,21(5):825-830
Plasma sprayed ceramic coatings are widely used for thermal barrier coating applications. Commercially available mullite powder particles and a mixture of mechanically alloyed alumina and silica powder particles were used to deposit mullite ceramic coatings by plasma spraying. The coatings were deposited at three different substrate temperatures (room temperature, 300?°C, and 600?°C) on stainless steel substrates. Microstructure and morphology of both powder particles as well as coatings were investigated by using scanning electron microscopy. Phase formation and degree of crystallization of coatings were analyzed by x-ray diffraction. Differential thermal analysis (DTA) was used to study phase transformations in the coatings. Results indicated that the porosity level in the coatings deposited using mullite initial powder particles were lower than those deposited using the mixed initial powder particles. The degree of crystallization of the coatings deposited using the mixed powder particles was higher than that deposited using mullite powder particles at substrate temperatures of 25 and 300?°C. DTA curves of the coatings deposited using the mixed powders showed some transformation of the retained amorphous phase into mullite and alumina. The degree of crystallization of the as sprayed coatings using the mixed powder particles was significantly increased after post deposition heat treatments. The results indicated that the mechanically alloyed mixed powder can be used as initial powder particles for deposition of mullite coatings instead of using mullite powders. 相似文献
11.
Composite coatings made of diamond powders and borosilicate glass have been deposited on stainless steel substrates by electrophoretic co-deposition. Ethanol and acetone suspensions containing diamond powders of particle size 1-2 μm and borosilicate glass powders of size 0.1-0.5 μm were used. Electrophoretic deposition (EPD) parameters were optimized by a trial-and-error-approach. Microstructures of deposited and sintered coatings were investigated by XRD and SEM analysis. The results show that applied voltages up to 10 V led to thin and incomplete coatings. Voltages higher than 50 V resulted in uneven coatings with uncontrolled thickness and poor uniformity. The best results were achieved using ethanol suspensions. Smooth, uniform and dense coatings with diamond and glass particles distributed uniformly were obtained under applied voltages in the range of 30-50 V and a deposition time of 4 min. The concentration ratio of diamond to borosilicate glass in the composite coatings was in good correlation with the original ratio in suspension, thus control of the coating microstructure and composition is possible. During sintering at 900 °C, the glass particles softened; sintered by viscous flow and spread over the diamond particles surface. Thus a glass layer forms protecting the diamond from oxidization or graphitization and bonding the diamond particles together. 相似文献
12.
Reactive plasma spraying of wear-resistant coatings 总被引:8,自引:0,他引:8
A method for producing wear-resistant, carbide-reinforced coatings has been investigated. A conventional low-pressure plasma
gun has been modified with a downstream reactor into which carbon-containing gases are mixed, heated, and disassociated. The
disassociated gas ions—H* and C* —are subsequently brought into contact with heated, molten metal matrix powders. Experiments
with NiCr/Ti blends and W powders have shown that uniformly dispersed carbides such as, TiC, Cr^Cy, WC, and W2C were formed
in situ on the metal precursor powders during deposition. The in situ formed particles, being formed directly from the matrices,
show excellent matrix cohesion and lead to high and uniform deposit microhardnesses. The process is described and several
evaluations of materials, reactive gases, and spray conditions are reported. Microanalysis of the coatings are presented,
microhardness values are reported, and XRD identifies the in situ formed phases. 相似文献
13.
Holger Kassner Roberto Siegert Dag Hathiramani Robert Vassen Detlev Stoever 《Journal of Thermal Spray Technology》2008,17(1):115-123
Conventional thermal spray processes as atmospheric plasma spraying (APS) have to use easily flowable powders with a size
up to 100 μm. This leads to certain limitations in the achievable microstructural features. Suspension plasma spraying (SPS)
is a new promising processing method which employs suspensions of sub-micrometer particles as feedstock. Therefore much finer
grain and pore sizes as well as dense and also thin ceramic coatings can be achieved. Highly porous coatings with fine pore
sizes are needed as electrodes in solid-oxide fuel cells. Cathodes made of LaSrMn perovskites have been produced by the SPS
process. Their microstructural and electrochemical properties will be presented. Another interesting application is thermal
barrier coating (TBC). SPS allows the manufacture of high-segmented TBCs with still relatively high porosity levels. In addition
to these specific applications also the manufactures of new microstructures like nano-multilayers and columnar structures
are presented. 相似文献
14.
Plasma-sprayed thermal barrier coatings (TBCs) have been used to extend the life of combustors. Electron beam physical vapor deposited (EB-PVD) ceramic coating has been developed for more demanding rotating as well as stationary turbine components. Here 3 kW RF magnetron sputtering equipment was used to gain zirconia ceramic coatings on hollow turbine blades and vanes, which had been deposited NiCrAIY by cathodic arc deposition. NiCrAlY coating surface was treated by shot peening; the effects of shot peening on the residual stress are presented. The results show that RF sputtered TBCs are columnar ceramics, strongly bonded to metal substrates. NiCrAlY bond coat is made of β, γ‘ and Cr phases, ZrO2 ceramic layer consists of t‘ and c phases. No degradation occurs to RF ceramic coatings after 100 h high temperature oxidation at 1150℃ and 500 thermal cycles at 1150℃ for 2 min, air-cooling. 相似文献
15.
Modeling of plasma spraying of two powders 总被引:2,自引:0,他引:2
B. Dussoubs A. Vardelle G. Mariaux P. Fauchais N. J. Themelis 《Journal of Thermal Spray Technology》2001,10(1):105-110
The behavior of metal and ceramic powders co-sprayed through a plasma jet was simulated using a commercial fluid dynamics
model in which the particles are considered as discrete Langrangian entities. Computations were carried out for the plasma
jet and the injected particles using (a) a steady-state three-dimensional (3-D) jet and (b) a simplified two-dimensional (2-D)
model. An analytical method was used to estimate the appropriate injection velocities for the metal and ceramic particles,
injected through opposing nozzles perpendicular to the plasma flow, so that their “mean” trajectories would impinge on the
same area on the target surface. Comparison of the model projections with experimental measurements showed that this method
of computation can be used to predict and control the behavior of particles of widely different properties. 相似文献
16.
S. Niezgoda V. Gupta R. Knight R. A. Cairncross T. E. Twardowski 《Journal of Thermal Spray Technology》2006,15(4):731-738
The high-velocity oxyfuel (HVOF) combustion spraying of dry ball-milled nylon-11/ceramic composite powders is an effective,
economical, and environmentally sound method for producing semicrystalline micron and nanoscale reinforced polymer coatings.
Composite coatings reinforced with multiple scales of ceramic particulate material are expected to exhibit improved load transfer
between the reinforcing phase and the matrix due to interactions between large and small ceramic particles. An important step
in developing multiscale composite coatings and load transfer theory is determining the effect of reinforcement size on the
distribution of the reinforcement and the properties of the composite coating.
Composite feedstock powders were produced by dry ball-milling nylon-11 together with 7, 20, and 40 nm fumed silica particles,
50 and 150 nm fumed alumina particles, and 350 nm, 1, 2, 5, 10, 20, 25, and 50 μm white calcined alumina at 10 vol.% overall
ceramic phase loadings. The effectiveness of the ball-milling process as a function of reinforcement size was qualitatively
evaluated by scanning electron microscopy+energy dispersive x-ray spectroscopy (SEM+EDS) microanalysis and by characterizing
the behavior of the powder during HVOF spraying. The microstructures of the sprayed coatings were characterized by optical
microscopy, SEM, EDS, and x-ray diffraction (XRD). The reinforcement particles were found to be concentrated at the splat
boundaries in the coatings, forming a series of interconnected lamellar sheets with good three-dimensional distribution. The
scratch resistance of the coatings improved consistently and logarithmically as a function of decreasing reinforcement size
and compared with those of HVOF sprayed pure nylon-11.
This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials
Park, OH, 2006. 相似文献
17.
Gary Paul Kennedy Kwang-Young Lim Young-Wook Kim In-Hyuck Song Hai-Doo Kim 《Metals and Materials International》2011,17(4):599-605
Porous self-bonded silicon carbide (SBSC) ceramics were fabricated from SiC powders with various particle sizes (0.7 μm, 25
μm, 50 μm, 65 μm), plus Si, C and boron (as a sintering additive). The effects of submicron (0.7 μm) SiC particle incorporation
into the SBSC and the SiC particle size (25 μm, 50 μm, 65 μm) on the flexural strength and porosity of the ceramics were investigated
as a function of sintering temperature. Incorporating 0.7 μm SiC particles into the ceramic material containing 25 μm SiC
particles increased the flexural strength by 3 times, from 11.7 MPa up to 35.5 MPa after sintering at 1800 °C. Simultaneously,
the porosity was reduced by ∼5 %. Furthermore, the flexural strength of ceramic with 25 μm SiC particles was superior to that
with 65 μm SiC particles. Generally, the flexural strength of the SBSC increased as, both, a function of submicron SiC particle
incorporation along with relatively small micron-sized particles (25 μm) in the microstructure of the ceramic plus increased
sintering temperature. 相似文献
18.
The structure, hardness, abrasion, and erosion wear of Cr-Mo white iron (containing approximately 28 % Cr and 1 % Mo) heat
treated at certain temperatures were studied. Results show that the heat treatment of white iron changes the structures and
properties; that is morphology, amount, size, and distribution of secondary phases are affected. When white iron was heated
at 800 to 850 ‡C the secondary phase precipitated at the phase boundary, making the abrasion and erosion wear worse. When
the iron was heated at 900 to 950 ‡C, the secondary phase precipitated dispersively at the matrix, and the corrosion wear
was optimum. If the iron is heated at 1000 to 1050 ‡C, the resistance of abrasion is inhibited, as the secondary phases precipitate
in large amounts, and the hardness is increased. When the white iron is tempered at 500 to 600 ‡C, the resistance of abrasion
is better. 相似文献
19.
E. A. Levashov V. V. Kurbatkina A. A. Zaitsev S. I. Rupasov E. I. Patsera A. A. Chernyshev Ya. V. Zubavichus A. A. Veligzhanin 《The Physics of Metals and Metallography》2010,109(1):95-105
Precipitation hardening alloys of the Ti-Ta-C and Ti-Zr-C systems produced by self-propagating high-temperature synthesis
(SHS) have been studied. Optimum compositions of the alloys and heat-treatment conditions, under which the decomposition of
supersaturated solid solution accompanied by the precipitation of fine particles both inside carbide grains and at their boundaries
occurs, have been determined. The precipitation hardening ceramic materials exhibit high hardness (∼15–23 GPa) and heat resistance
(the mass increase of the Ti-9.4% Ta-10.5% C alloy is less than 8 g/m2 during a 50-h exposure in air at 800°C) and can be recommended for the application as materials for deposited multifunctional
coatings, high-temperature contacts, evaporation crucibles, and abrasion-resistive tools. 相似文献
20.
H. Y. Koo J. H. Kim S. K. Hong J. M. Han Y. N. Ko Y. C. Kang S. H. Kang S. B. Cho 《Metals and Materials International》2010,16(6):941-946
Aggregated Fe powders comprising elongated and aggregated particles used in the production of heat pellets for application
in thermal batteries were prepared by spray pyrolysis. Iron oxide powders comprising dense and hollow particles were prepared
by spray pyrolysis from spray solutions containing various types of Fe precursors. Iron oxide powders prepared from iron chloride
and iron nitrate precursors were comprised of spherical and micron-sized particles. On the other hand, iron oxide powders
prepared from iron oxalate were comprised of large, hollow, and thin-walled particles. The Brunauer-Emmett-Teller (BET) surface
areas of iron oxide powders prepared from iron chloride, iron nitrate, and iron oxalate precursors were 17.5, 71.9, and 78.5
m2 g−1, respectively. At a low reduction temperature of 550 °C, iron oxide powders prepared from iron oxalate afforded loosely aggregated
Fe powders comprised of elongated and loosely aggregated particles, with a BET surface area of 5.9 m2 g−1. The heat pellets prepared from Fe powders reduced at 550 °C and composed of fine primary powders had an ignition sensitivity
of 0.9 W and a burn rate of 10 cm s−1. 相似文献