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1.
Yttrium silicate (Y2 SiO5 ) coatings complement SiC coatings for protecting ceramic multilayer composite materials based on carbon-fiber-reinforced SiC composites (C-SiC). Thick (100 μm), dense Y2 SiO5 coatings were prepared by dip coating, using concentrated aqueous slips. The resulting phases were studied by taking into account the simultaneous presence of oxide and non-oxide materials, which affected the chemical stability of the coatings. Thick, mechanically stable coatings were obtained by sintering in carbon crucibles and a SiC bed in an argon-flow furnace. Pure Y2 SiO5 coatings completely separated from the SiC substrates. A high percentage of Y2 Si2 O7 was necessary to fit the thermal expansion coefficients and ensure the stability of the coatings. Oxidation resistance of the coated substrates was investigated by isothermal and stepwise oxidation tests. 相似文献
2.
C. M. Weyant K. T. Faber J. D. Almer J. V. Guiheen 《Journal of the American Ceramic Society》2005,88(8):2169-2176
Due to its coefficient of thermal expansion (CTE) and phase stability up to 1360°C, tantalum oxide (Ta2 O5 ) was identified and investigated as a candidate environmental barrier coating for silicon nitride-based ceramics. Ta2 O5 coatings were plasma sprayed onto AS800, a silicon nitride ceramic from Honeywell International, and subjected to static and cyclic heat treatments up to 1200°C in air. Cross-sections from coated and uncoated substrates were polished and etched to reveal the effect of heat treatments on microstructure and grain size. As-sprayed coatings contained vertical cracks that healed after thermal exposure. Significant grain growth that was observed in the coatings led to microcracking due to the anisotropic CTE of Ta2 O5 . High-energy X-ray diffraction was used to determine the effect of heat treatment on residual stress and phases. The uncoated substrates were found to have a surface compressive layer before and after thermal cycling. Coating stresses in the as-sprayed state were found to be tensile, but became compressive after heat treatment. The microcracking and buckling that occurred in the heat-treated coatings led to stress relaxation after long heat treatments, but ultimately would be detrimental to the function of the coating as an environmental barrier by affording open pathways for volatile species to reach the underlying ceramic. 相似文献
3.
Svetlana M. Zemskova Camille Y. Jones Kevin M. Cooley J. Allen Haynes 《Journal of the American Ceramic Society》2004,87(12):2201-2207
Fabrication of mullite (3Al2 O3 ·2SiO2 ) coatings by chemical vapor deposition (CVD) using AlCl3 –SiCl4 –H2 –CO2 gas mixtures was studied. The resultant CVD mullite coating microstructures were sensitive to gas-phase composition and deposition temperature. Chemical thermodynamic calculations performed on the AlCl3 –SiCl4 –H2 –CO2 system were used to predict an equilibrium CVD phase diagram. Results from the thermodynamic analysis, process optimization, and effects of various process parameters on coating morphology are discussed. Dense, adherent crystalline CVD mullite coatings ∼2 μm thick were successfully grown on Si3 N4 substrates at 1000°C and 10.7 kPa total pressure. The resultant coatings were 001 textured and contained well-faceted grains ∼0.3–0.5 μm in size. 相似文献
4.
Ozer Unal Terrence E. Mitchell Arthur H. Heuer 《Journal of the American Ceramic Society》1994,77(4):984-992
The microstructures of ZrO2 –20 wt% Y2 O3 thermal barrier coatings formed by electron beam-physical vapor deposition on a Nibase superalloy have been studied by transmission electron microscopy. The coating systems consist of several layers, including a superalloy substrate, a bond coat, an Al2 O3 scale, and the PVD coating. The overall ceramic thermal barrier coatings were characterized, with special emphasis being given to the α-Al2 O3 scale which forms between the bond coat and the ZrO2− Y2 O3 coating. The oxide scale exhibited various morphologies in different coating systems; the majority of the porosity formed in this region for all coatings. 相似文献
5.
Analysis of Phase Distribution for Ceramic Coatings Formed by Microarc Oxidation on Aluminum Alloy 总被引:26,自引:0,他引:26
Wenbin Xue Zhiwei Deng Yonchun Lai Ruyi Chen 《Journal of the American Ceramic Society》1998,81(5):1365-1368
The phase distribution for ceramic coatings formed by microarc oxidation (MAO) on 2024 aluminum alloy was investigated using X-ray diffraction. The results showed that the ceramic coatings mainly consisted of α-Al2 O3 and γ-Al2 O3 phases. The percentage of α-Al2 O3 gradually increased from the external surface to the interface between the coating and the substrate of samples. The surface layer of coatings mainly contained the γ-Al2 O3 phase, and its fraction of the composition remained almost constant with oxidation time. It is believed that the difference in the amounts of α-Al2 O3 and γ-Al2 O3 phases in the different layers of coatings was caused by the various cooling rates of molten Al2 O3 , which temporarily existed in the microarc zone. 相似文献
6.
Yigal D. Blum Jochen Marschall David Hui Steven Young 《Journal of the American Ceramic Society》2008,91(5):1453-1460
A new process to form thick and dense ultra-high-temperature ceramic (UHTC) composite coatings over SiC surfaces is described. Coatings of ZrB2 /SiC/(ZrC) thicker than 100 μm are formed by a reaction-bonded SiC (RBSC) approach based on Si infiltration into ZrB2 /C preform coating. The residual Si, typically found in RBSC, can be eliminated efficiently to provide a coating material that performs at temperatures above 1500°C. The process is performed at 1500°C in Ar at ambient pressure. The interface between the in situ formed SiC and the Zr phases is very tight, as is the interface with the substrate.
The ZrB2 particles used in this process are rearranged in their morphology and an additional new phase containing Zr–C is formed. The coatings exhibit excellent integrity, hardness, and bonding to the tested substrates. A preliminary oxidation study indicates good protection of substrates at 1500°C under both passive and active oxidation conditions, provided that the coatings have sufficient thickness. 相似文献
The ZrB
7.
Zhongping Yao Zhaohua Jiang Xuelin Zhang 《Journal of the American Ceramic Society》2006,89(9):2929-2932
A micro-plasma oxidation (MPO) technique has been developed in recent years, by which ceramic coatings are reported to possess improved properties and promising application prospects in many fields. The aim of this work was to study the effect of sodium sulfate, as an additive in the zirconate system, on the structure and corrosion resistance of ceramics coatings containing zirconium oxide grown on Ti–6Al–4V by MPO process. The phase composition, morphology, and element distribution in the coating were investigated by X-ray diffractometry, scanning electron microscopy, and energy distribution spectroscopy. Meanwhile, the corrosion resistance of the coated samples was examined by polarizing curves and potentiodynamic anodic curves in 3.5% NaCl solution. The results show that ceramic coatings were composed of m -ZrO2 , t -ZrO2 , and KZr2 (PO4 )3 . The Ti content in the coating near the substrate decreased sharply, and then remained at 5 wt% or so through the coating, while the Zr content near the substrate increased greatly, and then remained at about 55 wt% through the coating. The addition of sodium sulfate did not change the composition of the coatings, but increased the relative proportion of zirconium oxide to KZr2 (PO4 )3 in the coating. Sodium sulfate decreased the thickness of the coating, while improving the density of the coatings. Moreover, the addition of the sodium sulfate improved the corrosion resistance of the coated samples in a 3.5% NaCl solution, whether considering localized pitting corrosion resistance or uniform corrosion resistance. 相似文献
8.
Alumina/Epoxy Interpenetrating Phase Composite Coatings: I, Processing and Microstructural Development 总被引:1,自引:0,他引:1
Interpenetrating phase composite (IPC) coatings consisting of continuously connected Al2 O3 and epoxy phases were fabricated. The ceramic phase was prepared by depositing an aqueous dispersion of Al2 O3 (0.3 μm) containing orthophosphoric acid, H3 PO4 , (1–9.6 wt%, solid basis) and heating to create phosphate bonds between particles. The resulting ceramic coating was porous, which allowed the infiltration and curing of a second-phase epoxy resin. The effect of dispersion composition and thermal processing conditions on the phosphate bonding and ceramic microstructure was investigated. Reaction between Al2 O3 and H3 PO4 generated an aluminum phosphate layer on particle surfaces and between particles; this bonding phase was initially amorphous, but partially crystallized upon heating to 500°C. Flexural modulus measurements verified the formation of bonds between particles. The coating porosity (and hence epoxy content in the final IPC coating) decreased from ∼50% to 30% with increased H3 PO4 loading. The addition of aluminum chloride, AlCl3 , enhanced bonding at low temperatures but did not change the porosity. Diffuse reflectance FTIR showed that a combination of UV and thermal curing steps was necessary for complete curing of the infiltrated epoxy phase. Al2 O3 /epoxy IPC coatings prepared by this method can range in thickness from 1 to 100 μm and have potential applications in wear resistance. 相似文献
9.
Edda Stern Madeleine Heyder Franziska Scheffler 《Journal of the American Ceramic Society》2009,92(10):2438-2442
Surface structures in micrometer scale were prepared on different substrates by a coating process using particle-filled slurries based on a blend of preceramic polymers. Parameters like solvent fraction, substrate material, filler particle size, and layer thickness were varied. Demixing reactions of solvent and polymers led to surface structures with pores of 1–60 μm in diameter. The solubility parameters δt of the polysiloxanes used are about 18.7 MPa1/2 for poly(methyl phenyl vinyl siloxane) and 19.5 MPa1/2 for poly(methyl siloxane), respectively. By pyrolysis of the green layers, ceramic coatings were obtained by keeping the particular surface structures. 相似文献
10.
A procedure for the formation of A12 O3 coatings as diffusion barriers between ductile reinforcements (e.g., Nb and Ta) and intermetallic matrices (e.g., MoSi2 and NiAl) is described. The coating technique involved sol-gel processing of alumina -forming sols with the addition of submicrometer-sized A12 O3 particles. Cracking in the coatings, a typical shortcoming of alumina sol-gel coating, was overcome by the addition of the fine particles into the sols. The surface charge of the A12 O3 particles was adjusted to be the same as the AIO(OH) colloids in the sols and electrophoresis was used to codeposit A12 O3 and AIO(OH) onto the surfaces of the reinforcements. The alumina gel derived from the sols acted as binder for the alumina particles, while the particles reduced the shrinkage of the sol-gel coatings and promoted the formation of dense coatings. The thickness of the coatings could be easily controlled without cracking and the effectiveness of the coatings as diffusion barriers was improved substantially. 相似文献
11.
Mark A. Borst Woo Y. Lee Ying Zhang Peter K. Liaw 《Journal of the American Ceramic Society》1997,80(6):1591-1594
Monoclinic ZrO2 was deposited on several metallic and ceramic substrates by reacting ZrCl4 , CO2 , and H2 at temperatures of 800° to 1050°C. Ni substrates reacted significantly in the ZrO2 coating environment since the coating was porous and contained a considerable amount of Ni. In contrast, the coating deposited on SiC and aluminoborosilicate fibers was highly crystalline, faceted, and dense without any apparent interaction with the substrate materials. 相似文献
12.
Determining the Critical Strain Energy Release Rate of Plasma-Sprayed Coatings Using a Double-Cantilever-Beam Technique 总被引:1,自引:0,他引:1
A double-cantilever-beam (DCB) method for determining critical strain energy release rate (GIc ) values from plasma-sprayed coatings is described in detail. This approach, involving acoustic emission (AE) methodology, yielded up to 25 results per specimen and was successful in providing cohesive GIc values for plasma-sprayed coatings of Al2 O3 -2.5 wt% TiO2 , Ni-20 wt% Al, as well as two ostensibly identical, 99.5% commercially pure Al2 O3 coatings. Adhesive G Ic data from Al2 O3 -40 wt% TiO2 coatings was also obtained. Results showed a G Ic dependence on crack length, and a number of possibilities, based on fractography, the AE response of the coatings during testing, and crack velocity measurements, are advanced to explain this occurrence. Differences in G Ic values between coatings were found to correlate with differences in powder/coating properties. The DCB method was also used to investigate batch differences and the effect on toughness of sealing an alumina coating. Problems associated with this method of testing are addressed. 相似文献
13.
Yong W. Bae Woo Y. Lee Charles S. Yust Peter J. Blau Theodore M. Besmann 《Journal of the American Ceramic Society》1996,79(4):819-824
Composite coatings containing discrete crystalline phases of TiN and MoS2 were deposited on Si, graphite, and Ti-6A-14V alloy substrates by simultaneous chemical vapor deposition. MoF6 and H2 S were utilized as the precursors for MoS2 formation, while Ti((CH3 )2 N)4 and NH3 were used for TiN deposition. The composition and microstructure of the coatings were investigated by X-ray diffraction, Auger electron spectroscopy, and transmission electron microscopy. The molar ratios of TiN and MoS2 in the composite microstructure could be controlled by adjusting the MoF6 concentration in the reagent mixture. Encouraging friction and wear characteristics against silicon nitride were obtained for a composite coating which was rich in MoS2 at the coating surface, with TiN as the major phase near the substrate interface. Friction coefficients at room temperature in air were typically in the range of 0.07 to 0.3. The friction coefficients remained comparable at 573 K, but increased to 0.7 to 1.0 at 673 K. A friction coefficient value of −0.3 was, however, obtained from a composite coating tested at 973 K. 相似文献
14.
Structure and Properties of ZrO2 Ceramic Coatings on AZ91D Mg Alloy by Plasma Electrolytic Oxidation
Zhongping Yao Huihui Gao Zhaohua Jiang Fuping Wang 《Journal of the American Ceramic Society》2008,91(2):555-558
ZrO2 ceramic coatings were prepared in situ on an AZ91D Mg alloy by plasma electrolytic oxidation in a K2 ZrF6 solution. The phase composition and the surface morphology of the coatings were examined with X-ray diffraction and scanning electron microscopy. The thermal shock resistance of the coatings was evaluated by a thermal shock test. The corrosion resistance of the coated samples was examined by the polarizing curve method in a 3.5% NaCl solution. The prepared coating was composed of t -ZrO2 and a small amount of c -ZrO2 . There were many residual discharging channels on the coating surface. The coated samples showed excellent thermal shock resistance under 500°C, which improved with increasing frequency or decreasing current density or PEO time. Besides, the coating improved the corrosion resistance of AZ91D Mg alloy considerably. In the experiments, the corrosion current density of the coated samples prepared under 1000 Hz was the least, which also decreased with the current density during the PEO process. 相似文献
15.
Claus H. Rüscher Holger Fritze Günter Borchardt Thomas Witke Bernd Schultrich 《Journal of the American Ceramic Society》1997,80(12):3225-3228
Mullite (3Al2 O3 ·2SiO2 ) coatings on SiC substrates and SiC precoated carbon/carbon composite (C/C-Si-SiC) substrates were produced by pulsed laser deposition (PLD) using pressed mullite powder targets. The layers can be characterized efficiently by IR reflection spectroscopy in the spectral range between 650 and 5000 cm−1 . The deposited coatings turn into mullite upon oxidation in air at temperatures between 1400° and 1600°C. Fabry-Perot interferences indicate a high quality and homogeneity of the mullite coating/SiC substrate interface. Amorphous SiO2 gradually forms during prolonged heating or at higher temperatures. 相似文献
16.
Yong W. Bae Woo Y. Lee David P. Stinton 《Journal of the American Ceramic Society》1995,78(5):1297-1300
Crystalline β-Ta2 O5 coatings were deposited on hot-isostatically-pressed Si3 N4 by reacting TaCl5 with H2 and CO2 in the temperature range of 1000°–1300°C and at a pressure of 660 Pa. The Ta2 O5 coatings generally consisted of wellcoalesced 2–3 μm grains, resulting in the formation of a nonporous coating morphology. However, the presence of microcracks on the as-deposited surface was consistently observed. The surface morphology, texture, and growth rate of the coatings were examined as a function of deposition parameters. 相似文献
17.
A rhabdophane (LaPO4 ·nH2 O) sol with fine spherical particles was used to coat Nextel™ 720 fiber tows continuously with monazite (LaPO4 ). The coatings are compared with those made previously from rod-shaped particles. The coated fibers were heat-treated at 1000°–1300°C for 1, 10, and 100 h. The effect of heat treatment temperature and time on coating microstructure was characterized by scanning electron microscopy and transmission electron microscopy, and the strengths of the coated fibers were measured after coating and heat treatment. Grain shapes and grain growth rates were measured. Coating thickness uniformity was quantified by a fit to a truncated extreme-value distribution. Coating hermeticity was evaluated by analysis of grain growth rates. The spherical particles promote more rapid coating densification and local hermeticity, but introduce problems with sintering shrinkage cracking that are not present in coatings derived from rod-shaped particles. 相似文献
18.
Rachman Chaim Sylvie Almaleh-Rockman Leah Gal-Or Harro Bestgen 《Journal of the American Ceramic Society》1994,77(12):3202-3208
SiC and TiB2 were electrochemically coated with Cr2 O3 from a 0.1 M aqueous solution of chromium nitrate hydrate with ethanol additives. On both substrate materials poly-crystalline Cr2 O3 was formed at current densities from 5 to 50 mA/cm2 and deposition durations of 5 to 30 min. The coating weight increased with current density and with deposition time. The as-deposited coatings contained microcracks due to drying shrinkage. Microstructural observations indicate that sintering of the Cr2 O3 coatings on TiB2 at 1100°C for 1 n in a reducing atmosphere in a closed graphite crucible causes the densification of the coating via a liquid phase, which forms by oxidation of TiB2 . Under similar conditions, the Cr2 O3 coatings on SiC may be sintered via an evaporation–condensation mechanism. 相似文献
19.
Michael L. Auger Anita Sengupta Vinod K. Sarin 《Journal of the American Ceramic Society》2000,83(10):2429-2435
The corrosion characteristics of bulk alumina, SiC, mullite, and CVD mullite coatings on SiC in contact with coal slag were investigated. Uncoated SiC corroded in the presence of coal slag, forming mixed FeSi phases and carbon. Bulk Al2 O3 and slag formed a diffusional phase believed to be the spinel hercynite (Fe,Mg)O·(Al,Fe)2 O3 . After exposure to coal slag, a compositional difference was observed at bulk mullite/coal slag interfaces, yet this diffusional phase did not appreciably degrade the mullite samples and no cracking was observed. CVD mullite coatings offered protection to SiC in a simulated coal gasification atmosphere with corrosion protection dependent on the uniformity of the coating. Microprobe analysis of the CVD mullite coating/slag interface showed the formation of a Fe(Mg)Al. 相似文献
20.
Yongsheng Liu Laifei Cheng Litong Zhang Wenbin Yang Yongdong Xu 《International Journal of Applied Ceramic Technology》2008,5(3):305-312
Methane (CH4 ) and propylene (C3 H6 ) were used to fabricate a boron–carbon coating by a low-pressure chemical vapor deposition (LPCVD) technique. The effects of carbon precursors on the phase, microstructure, and bonding state of the deposits have been investigated. X-ray diffraction results show that the 2θ value of the deposit from the C3 H6 precursor shifts to 25.78° when the coating is deposited at 1223 K, and shifts to 26.1° when deposited at 1273 K, compared with the 2θ value of the pyrocarbon (PyC) peak deposited by LPCVD, which is 25.42°, and no boron–carbon (B–C) compound peak exists. However, the phases of coating deposited from CH4 include B25 C, B13 C2 , elemental carbon, and boron. X-ray photoelectron spectroscopy (XPS) results show that the percent contents of boron atom in the coatings from the CH4 precursor are 61.18% and 67.78% when deposited at 1223 and 1273 K, respectively, much higher than that from the C3 H6 precursor, 10.85% and 15.30%, respectively. Scanning electron microscopy (SEM) results show that the coatings deposited from CH4 have a coarse crystal-like morphology; however, the coatings deposited from the C3 H6 precursor are smooth. The formation of PyC from C3 H6 is more facile than that from CH4 , which leads to differences in the phase, atom content, and microstructure of coatings from CH4 and C3 H6 precursors. 相似文献