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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.
New attachment for controlling gas flow in the HVOF process 总被引:1,自引:0,他引:1
During the decade, the high-velocity oxyfuel (HVOF) process proved to be a technological alternative to the many conventional
thermal spray processes. It would be very advantageous to design a nozzle that provides improved performance in the areas
of deposition efficiency, particle in-flight oxidation, and flexibility to allow deposition of ceramic coatings. Based on
a numerical analysis, a new attachment to a standard HVOF torch was modeled, designed, tested, and used to produce thermal
spray coatings according to the industrial needs mentioned above. Performance of the attachment was investigated by spraying
several coating materials including metal and ceramic powders. Particle conditions and spatial distribution, as well as gas
phase composition, corresponding to the new attachment and the standard HVOF gun, were compared. The attachment provides better
particle spatial distribution, combined with higher particle velocity and temperature.
The original version of this article was published as part of the ASM Proceedings, Thermal Spray 2003: Advancing the Science and Applying the Technology, International Thermal Spray Conference (Orlando, FL), 5–8 May, 2003, Basil R. Marple and Christian Moreau, Ed., ASM International,
2003. 相似文献
3.
High-velocity oxyfuel (HVOF) spraying of WC-12Co was performed using a feedstock in which the WC phase was either principally
in the micron size range (conventional) or was engineered to contain a significant fraction of nanosized grains (multimodal).
Three different HVOF systems and a wide range of spray parameter settings were used to study the effect of in-flight particle
characteristics on coating properties. A process window with respect to particle temperature was identified for producing
coatings with the highest resistance to dry abrasion. Although the use of a feedstock containing a nanosized WC phase produced
harder coatings, there was little difference in the abrasion resistance of the best-performing conventional and multimodal
coatings. However, there is a potential benefit in using the multimodal feedstock due to higher deposition efficiencies and
a larger processing window.
The original version of this article was published as part of the ASM Proceedings, Thermal Spray 2003: Advancing the Science and Applying the Technology, International Thermal Spray Conference (Orlando, FL), May 5–8, 2003, Basil R. Marple and Christian Moreau, Ed., ASM International,
2003. 相似文献
4.
Nanostructured titania (TiO2) coatings were produced by high-velocity oxyfuel (HVOF) spraying. They were engineered as a possible candidate to replace
hydroxyapatite (HA) coatings produced by thermal spray on implants. The HVOF sprayed nanostructured titania coatings exhibited
mechanical properties, such as hardness and bond strength, much superior to those of HA thermal spray coatings. In addition
to these characteristics, the surface of the nanostructured coatings exhibited regions with nanotextured features originating
from the semimolten nanostructured feedstock particles. It is hypothesized that these regions may enhance osteoblast adhesion
on the coating by creating a better interaction with adhesion proteins, such as fibronectin, which exhibit dimensions in the
order of nanometers. Preliminary osteoblast cell culture demonstrated that this type of HVOF sprayed nanostructured titania
coating supported osteoblast cell growth and did not negatively affect cell viability.
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
5.
Hybrid plasma spraying combined with yttrium-aluminum-garnet laser irradiation was studied to obtain optimum zirconia coatings
for thermal barrier use. Zirconia coatings of approximately 150 μm thickness were formed on NiCrAlY bond coated steel substrates
both by means of conventional plasma spraying and hybrid plasma spraying under a variety of conditions. Post-laser irradiation
was also conducted on the plasma as-sprayed coating. The microstructure of each coating was studied and, for some representative
coatings, thermal barrier properties were evaluated by hot erosion and hot oxidation tests. With hybrid spraying, performed
under optimum conditions, it was found that a microstructure with appropriate partial densification and without connected
porosity was formed and that cracks, which are generally produced in the post-laser irradiation treatment, were completely
inhibited. In addition, hybrid spraying formed a smooth coating surface. These microstructural changes resulted in improved
coating properties with regard to hardness, high temperature erosion resistance, and oxidation resistance.
This paper originally appeared in Thermal Spray: Meeting the Challenges of the 21st Century; Proceedings of the 15th International Thermal Spray Conference, C. Coddet, Ed., ASM International, Materials Park, OH, 1998. This proceedings paper has been extensively reviewed according
to the editorial policy of the Journal of Thermal Spray Technology. 相似文献
6.
Ivosevic M. Knight R. Kalidindi S. R. Palmese G. R. Sutter J. K. 《Journal of Thermal Spray Technology》2005,14(1):45-51
High-velocity oxyfuel (HVOF) sprayed polyimide/WC-Co functionally graded (FGM) coatings with flame-sprayed WC-Co topcoats
have been investigated as solutions to improve the solid-particle erosion and oxidation resistance of polymer matrix composites
(PMCs) in the gas flow path of advanced turbine engines. Porosity, coating thickness, and volume fraction of the WC-Co phase
retained in the graded coating architecture were determined using standard metallographic techniques and computer image analysis.
The adhesive bond strength of three different types of coatings was evaluated according to ASTM D 4541. Adhesive/cohesive
strengths of the FGM coating were measured and compared with those of pure polyimide and polyimide/WC-Co composite coatings
and also related to the tensile strength of the uncoated PMC substrate perpendicular to the thickness. The FGM coatings exhibited
lower adhesive bond strengths (∼6.2 MPa) than pure polyimide coatings (∼8.4 MPa), and in all cases these values were lower
than the tensile strength (∼17.6 MPa) of the reference uncoated PMC substrate. The nature and locus of the failures were characterized
according to the percent adhesive and/or cohesive failure, and the interfaces tested and layers involved were analyzed by
scanning electron microscopy.
The original version of this paper was published as part of the ASM Proceedings, Thermal Spray 2003: Advancing the Science and Applying the Technology, International Thermal Spray Conference (Orlando, FL), 5–8 May, 2003, Basil R. Marple and Christian Moreau, Eds., ASM International,
2003. 相似文献
7.
Elastic modulus measurements via laser-ultrasonic and knoop indentation techniques in thermally sprayed coatings 总被引:1,自引:0,他引:1
R. S. Lima S. E. Kruger G. Lamouche B. R. Marple 《Journal of Thermal Spray Technology》2005,14(1):52-60
Nondestructive techniques for evaluating and characterizing coatings were extensively demanded by the thermal spray community;
nonetheless, few results have been produced in practice due to difficulties in analyzing the complex structure of thermal
spray coatings. Of particular interest is knowledge of the elastic modulus values and Poisson’s ratios, which are very important
when seeking to understand and/or model the mechanical behavior or to develop life prediction models of thermal spray coatings
used in various applications (e.g., wear, fatigue, and high temperatures). In the current study, two techniques, laser-ultrasonics
and Knoop indentation, were used to determine the elastic modulus of thermal spray coatings. Laser-ultrasonics is a noncontact
and nondestructive evaluation method that uses lasers to generate and detect ultrasound. Ultrasonic velocities in a material
are directly related to its elastic modulus value. The Knoop indentation technique, which has been widely used as a method
for determining elastic modulus values, was used to compare and validate the measurements of the laser-ultrasonic technique.
The determination of elastic modulus values via the Knoop indentation technique is based on the measurement of elastic recovery
of the dimensions of the Knoop indentation impression. The approach used in the current study was to focus on evaluating the
elastic modulus of very uniform, dense, and near-isotropic titania and WC-Co thermal spray coatings using these two techniques.
Four different coatings were evaluated: two titania coatings produced by air plasma spray (APS) and high-velocity oxyfuel
(HVOF) and two types of WC-Co coatings, conventional and multimodal (nanostructured and microsized particles), deposited by
HVOF.
The original version of this article was published as part of the ASM Proceedings, Thermal Spray 2003: Advancing the Science and Applying the Technology, International Thermal Spray Conference (Orlando, FL), 5–8 May, 2003, Basil R. Marple and Christian Moreau, Eds., ASM International,
2003. 相似文献
8.
A. J. Horlock Z. Sadeghian D. G. McCartney P. H. Shipway 《Journal of Thermal Spray Technology》2005,14(1):77-84
Recently, there has been considerable interest in producing cermet coatings with nanoscale carbide grains in the size range
50 to 500 nm. In this article, the production of nanoscale TiC grains in a Ni-based alloy matrix by reactive high-velocity
oxyfuel (HVOF) spraying of metastable Ni-Ti-C powder is reported. Mechanical alloying of a Ni(Cr) prealloyed powder and Ti
and C elemental powders was performed in a planar-type ball mill, and materials were characterized in detail using x-ray diffraction
(XRD) and scanning electron micros-copy (SEM). Phase changes were correlated with milling time and other processing conditions.
Results show that, by the selection of appropriate conditions, a metastable Ni-Ti-C powder could be obtained with the nominal
composition 50wt.%Ni-40wt.%Ti-10wt.%C. Following sieving and classification, powder was produced with a particle size range
of −38 to 8 μm, which is suitable for HVOF spraying. Coatings, approximately 250 μm thick, were deposited by HVOF spraying
onto mild steel substrates, and the microstructures formed were investigated. XRD showed that a self-propagating high-temperature
synthesis (SHS) reaction had occurred in the powder particles during spraying and that the principal phases present in the
coating were TiC and a Ni-rich solid solution; small quantities of NiTi, TiO2, and NiTiO3 were also present. SEM revealed that the coatings had a characteristic, splatlike morphology and that TiC formed as a nanoscale
dispersion, with a size range of ∼50 to 200 nm, within solidified splats. The microstructures of these reactively sprayed
Ni-TiC coatings are briefly compared with those observed in HVOF-sprayed coatings deposited using prereacted SHS powder.
The original version of this paper was published as part of the ASM Proceedings, Thermal Spray 2003: Advancing the Science and Applying the Technology, International Thermal Spray Conference (Orlando, FL), May 5–8, 2003, Basil R. Marple and Christian Moreau, Ed., ASM International,
2003. 相似文献
9.
A. A. Syed A. Denoirjean P. Denoirjean J. C. Labbe P. Fauchais 《Journal of Thermal Spray Technology》2005,14(1):117-124
Air engulfment by the plasma jet in air plasma spraying (APS) causes in-flight oxidation of metallic particles. This oxidation,
often complex and difficult to explain by classic diffusion-controlled oxidation, is governed by several mechanisms. This
paper highlights the possible in-flight oxidation mechanisms in metallic particles with a focus on the convective oxidation.
Two different types of austenitic stainless steel particles were air plasma sprayed using a direct current plasma gun and
were collected in an argon atmosphere. Preliminary experiments indicated that different mechanisms are likely to occur during
the in-flight oxidation of particles. The mass transfer from surface to interior of particle occurred, forming oxide nodules
within particles. The mass transfer is governed by convective movements inside liquid particles within the plasma jet core
due to the plasma-particle kinematic viscosity ratio greater than 50 and particle Reynolds number (Re) higher than 20. The
nodules were composed of metastable phases consisting of mixed oxide of Fe and Cr. Convective movements within particles ceased
roughly outside of the plasma jet core, and classic surface oxidation was found to be the dominant phenomenon forming the
surface oxide layer. Moreover, the molten surface oxide outside the jet core may become entrained toward the tail of the particle
if plasma conditions promote a higher particle Re number. The major oxide phase in collected particles was FeCr2O4, in a nonstoichiometric form of Fe3−x
Cr
x
O4.
The original version of this article was published as part of the ASM Proceedings, Thermal Spray 2003: Advancing the Science and Applying the Technology, International Thermal Spray Conference (Orlando, FL), May 5–8, 2003, Basil R. Marple and Christian Moreau, Ed., ASM International,
2003. 相似文献
10.
T. S. Sidhu A. Malik S. Prakash R. D. Agrawal 《Journal of Thermal Spray Technology》2007,16(5-6):844-849
The present work evaluates the oxidation and hot corrosion resistance of high velocity oxy-fuel (HVOF) sprayed WC-NiCrFeSiB
coating deposited on Ni-based superalloy (Superni 75) and Fe-based superalloy (Superfer 800H). The coated as well as uncoated
specimens were exposed to air and molten salt (Na2SO4-25% NaCl) environment at 800 °C under cyclic conditions. The thermogravimetric technique was used to establish the kinetics
of corrosion. The corrosion products were characterized using the combined techniques of x-ray diffraction (XRD), scanning
electron microscopy (SEM), and electron probe micro analyser (EPMA). The WC-NiCrFeSiB coating provides necessary resistance
against oxidation and hot corrosion to both the nickel and iron-based superalloys in the given environmental conditions at
800 °C. The oxides of active elements of the coatings, formed in the surface scale as well as at the boundaries of nickel
and tungsten rich splats, have contributed for the oxidation and hot corrosion resistance of WC-NiCrFeSiB coatings, as these
oxides act as barriers for the diffusion/penetration of the corrosive species through the coatings.
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
11.
A. H. Dent A. J. Horlock D. G. McCartney S. J. Harris 《Journal of Thermal Spray Technology》1999,8(3):399-404
The corrosion characteristics of two Ni-Cr-Mo-B alloy powders sprayed by the high-velocity oxy-fuel (HVOF) process have been
studied using potentiodynamic and potentiostatic corrosion analysis in 0.5 M H2SO4. The deposits were also microstructurally characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM)
(utilizing both secondary electron and backscattered electron modes), and transmission electron microscopy (TEM). Results
from the microstructural examination of the two alloys have revealed a predominantly amorphous/nanocrystalline face centered
cubic (fcc) matrix containing submicron boride precipitates as well as regions of martensitically transformed laths.
Apparent recrystallization of the amorphous matrix has also been observed in the form of cellular crystals with a fcc structure.
The oxide stringers observed at splat boundaries were found to be columnar grained α-Cr2O3, though regions of the spinel oxide NiCr2O4 with a globular morphology were also observed. The coatings of the two alloys exhibited comparable resistance to corrosion
in 0.5 M H2SO4, as revealed by potentiodynamic tests. They both had rest potentials approximately equal to −300 mV saturated calomel electrode
(SCE) and passive region current densities of ∼1 mA/cm2. Microstructural examination of samples tested potentiostatically revealed the prevalence of degradation at splat boundaries,
especially those where significant oxidation of the deposit occurred.
This paper originally appeared in Thermal Spray: Meeting the Challenges of the 21st Century; Proceedings of the 15th International Thermal Spray Conference, C. Coddet, Ed., ASM International, Materials Park, OH, 1998. This proceedings paper has been extensively reviewed according
to the editorial policy of the Journal of Thermal Spray Technology. 相似文献
12.
This article reports on a series of experiments with various high-velocity oxygen fuel spray systems (Jet Kote, Top Gun, Diamond
Jet (DJ) Standard, DJ 2600 and 2700, JP-5000, Top Gun-K) using different WC-Co and WC-Co-Cr powders. The microstructure and
phase composition of powders and coatings were analyzed by optical and scanning electron microscopy and x-ray diffraction.
Carbon and oxygen content of the coatings were determined to study the decarburization and oxidation of the material during
the spray process. Coatings were also characterized by their hardness, bond strength, abrasive wear, and corrosion resistance.
The results demonstrate that the powders exhibit various degrees of phase transformation during the spray process depending
on type of powder, spray system, and spray parameters. Within a relatively wide range, the extent of phase transformation
has only little effect on coating properties. Therefore, coatings of high hardness and wear resistance can be produced with
all HVOF spray systems when the proper spray powder and process parameters are chosen.
This paper originally appeared in Thermal Spray: Meeting the Challenges of the 21st Century; Proceedings of the 15th International Thermal Spray Conference, C. Coddet, Ed., ASM International, Materials Park, OH, 1998. This proceedings paper has been extensively reviewed according
to the editorial policy of the Journal of Thermal Spray Technology. 相似文献
13.
B. Somasundaram Ravikiran Kadoli M. R. Ramesh 《Journal of Thermal Spray Technology》2014,23(6):1000-1008
Corrosion of metallic structural materials at an elevated temperature in complex multicomponent gas environments are potential problems in many fossil energy systems, especially those using coal as a feedstock. Combating these problems involves a number of approaches, one of which is the use of protective coatings. The high velocity oxy fuel (HVOF) process has been used to deposit WC-Co/NiCrAlY composite powder on two types of Fe-based alloys. Thermocyclic oxidation behavior of coated alloys was investigated in the static air as well as in molten salt (Na2SO4-60%V2O5) environment at 700 °C for 50 cycles. The thermogravimetric technique was used to approximate the kinetics of oxidation. WC-Co/NiCrAlY coatings showed a lower oxidation rate in comparison to uncoated alloys. The oxidation resistance of WC-Co/NiCrAlY coatings can be ascribed to the oxide layer of Al2O3 and Cr2O3 formed on the outermost surface. Coated alloys extend a protective oxide scale composed of oxides of Ni and Cr that are known to impart resistance to the hot corrosion in the molten salt environment. 相似文献
14.
The Effect of Heat Treatment on the Oxidation Behavior of HVOF and VPS CoNiCrAlY Coatings 总被引:1,自引:0,他引:1
Free-standing VPS and HVOF CoNiCrAlY coatings were produced. The as-sprayed HVOF coating retained the γ/β microstructure of
the feedstock powder, and the VPS coating consisted of a single (γ) phase. A 3-h, 1100 °C heat treatment in vacuum converted
the single-phase VPS coating to a two-phase γ/β microstructure and coarsened the γ/β microstructure of the HVOF coating. Oxidation
of free-standing as-sprayed and heat-treated coatings of each type was carried out in air at 1100 °C for a duration of 100 h.
Parabolic rate constant(s), K
p, were determined for free-standing, as-sprayed VPS and HVOF coatings as well as for free-standing coatings that were heat
treated prior to oxidation. The observed increase in K
p following heat treatment is attributed to a sintering effect eliminating porosity from the coating during heat treatment.
The lower K
p values determined for both HVOF coatings compared to the VPS coatings is attributed to the presence of oxides in the HVOF
coatings, which act as the barrier to diffusion. Oxidation of the as-sprayed coatings produced a dual-layer oxide consisting
of an inner α-Al2O3 layer and outer spinel layer. Oxidation of the heat-treated samples resulted in a single-layer oxide, α-Al2O3. The formation of a thin α-Al2O3 layer during heat treatment appeared to prevent nucleation and growth of spinel oxides during subsequent oxidation. 相似文献
15.
B. G. Ravi S. Sampath R. Gambino J. B. Parise P. S. Devi 《Journal of Thermal Spray Technology》2006,15(4):701-707
Precursor plasma spray synthesis is an innovative and rapid method for making functional oxide ceramic coatings by starting
from solution precursors and directly producing inorganic films. This emerging method utilizes molecularly mixed precursor
liquids, which essentially avoids the handling and selection of powders, opening up new avenues for developing compositionally
complex functional oxide coatings. Precursor plasma spray also offers excellent opportunities for exploring the nonequilibrium
phase evolution during plasma spraying of multicomponent oxides from inorganic precursors. Although there have been efforts
in this area since the 1980s and early 1990s with the goal of synthesizing nanoparticles, only recently has the work progressed
in the area of functional systems. At the Center for Thermal Spray Research an integrated investigative strategy has been
used to explore the benefits and limits of this synthesis strategy. Water- and alcohol-based sol/solution precursors derived
from various chemical synthesis methods were used as feedstocks to deposit thin/thick films of spherical and nanostructured
coatings of yttrium aluminum garnet (YAG), yttrium iron garnet, lanthanum strontium manganate and Zr-substituted yttrium titanates,
and compositions of Y2O3-Al2O3 and their microstructural space centered around stoichiometric YAG. A detailed discussion of the salient features of the
radiofrequency induction plasma spraying approach, the results obtained in the investigations to develop various functional
oxide coatings, and process issues and challenges are presented.
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
16.
Mohammadreza DAROONPARVAR Muhamad Azizi Mat YAJID Noordin Mohd YUSOF Saeed FARAHANY Mohammad Sakhawat HUSSAIN Hamid Reza BAKHSHESHI-RAD Z. VALEFI Ahmad ABDOLAHI 《中国有色金属学会会刊》2013,23(5):1322-1333
A thermally grown oxide (TGO) layer is formed at the interface of bond coat/top coat. The TGO growth during thermal exposure in air plays an important role in the spallation of the ceramic layer from the bond coat. High temperature oxidation resistance of four types of atmospheric plasma sprayed TBCs was investigated. These coatings were oxidized at 1000 °C for 24, 48 and 120 h in a normal electric furnace under air atmosphere. Microstructural characterization showed that the growth of the TGO layer in nano NiCrAlY/YSZ/nano Al2O3 coating is much lower than in other coatings. Moreover, EDS and XRD analyses revealed the formation of Ni(Cr,Al)2O4 mixed oxides (as spinel) and NiO onto the Al2O3 (TGO) layer. The formation of detrimental mixed oxides (spinels) on the Al2O3(TGO) layer of nano NiCrAlY/YSZ/nano Al2O3 coating is much lower compared to that of other coatings after 120 h of high temperature oxidation at 1000 °C. 相似文献
17.
Thermal Barrier Coatings with HVOF NiCrAlY Bond Coat is prepared on nickel-based superalloy substrates. The lifetime of the
coating is about 1630 h for 1-h cycle at 1050 °C. Growth of the TGO (thermally grown oxide) approximately follows a parabolic
kinetics, and the TGO presents a bi-layered structure. Failure of the coating occurs near the interface between the mixed
oxides layer of TGO and top coat. A finite element method is employed to analyze the stress distribution in the coating. The
results show that maximum stresses occur at the top coat/TGO interface near the edge of the coating. The maximum radial stress
for TGO consisting of spinel and Al2O3 is about five times larger than that of Al2O3, while the maximum axial stress is about ten times larger. The mixed oxide layer of TGO plays an important role in the premature
failure of TBCs. 相似文献
18.
The oxidation of a low-pressure plasma-sprayed (LPPS) NiCrAlY coating on a nickel-base superalloy was studied at 1050 °C in flows of O2, and mixture of O2 and 5% H2O under atmospheric pressure. Water vapor has an obvious effect on the cyclic oxidation of the NiCrAlY coating. There is more decrease in weight gain when exposure to O2 is replaced by exposure to O2 + 5% H2O. The oxide formed on the LPPS NiCrAlY coating after cyclic oxidation in pure oxygen is composed mainly of Cr2O3, and a thin Al2O3-rich layer is formed at the interface between the Cr2O3-rich layer and the coating. The oxide formed on the LPPS NiCrAlY coating after cyclic oxidation in a mixture of O2 + H2O is composed of NiCr2O4, NiO and Cr2O3. The effect of water vapor on the oxidation of the NiCrAlY coating may be attributed to an increase in Ni and Cr cation transport, stress-corrosion cracking of Al2O3 and moisture-enhanced volatility of the Cr2O3 scale. 相似文献
19.
《中国有色金属学会会刊》2021,31(8):2428-2441
Al0.2CrFeNiCo and Al0.2CrFeNiCu high entropy alloys were deposited with high velocity oxygen fuel (HVOF) on 316L substrate. Later, a laser re-melting (LR) process was applied to enhancing the coating microstructure. LR process effects on dry sliding wear and oxidation behaviors were investigated. The mixture of powders with free elements led to the formation of inner oxides in HVOF coatings. The oxide and porosity were eliminated using LR. After LR, FCC was the dominant phase in both alloys, while BCC, sigma and Cr2O3 phases were observed in Al0.2CrFeNiCo alloy. The hardnesses of the Al0.2CrFeNiCo and Al0.2CrFeNiCu coatings after HVOF were HV 591 and HV 361, respectively. After LR, the hardnesses decreased to HV 259 and HV 270, respectively. Although HVOF coatings were most affected by increased load, they showed the highest wear resistance compared to other samples. The lowest wear resistance could be seen in the substrate. After the oxidation tests, HVOF coating layer was completely oxidized and also, the coating layer was delaminated from the substrate after 50 h oxidation due to its porous structure. LR coatings exhibited better oxidation performance. Al0.2CrFeNiCo was dominantly composed of Cr2O3, exhibiting a slower-growing tendency at the end of the oxidation tests, while Al0.2CrFeNiCu was composed of spinel phases. 相似文献
20.
Nidhi Rana R. Jayaganthan Satya Prakash 《Journal of Materials Engineering and Performance》2014,23(2):643-650
Present investigation deals with the hot corrosion behaviour of the NiCrAlY coatings deposited by HVOF technique on Superni76 under cyclic conditions at 900 °C in the presence of Na2SO4 + 60% V2O5 salt. The weight change behaviour of the coatings was followed with time up to 200 cycles and K p value was calculated for the hot corrosion process. Surface and cross-section of the corroded samples were examined by FESEM/EDS and XRD to follow the progress of corrosion up to 200 cycles. In earlier cycles, the corrosive species oxidised top surface of the coatings. With increasing number of cycles, oxidation of the coatings occurred up to 40-μm depth. A Cr-depleted band was seen below the oxide scale. Further increase in number of cycles led to migration and oxidation of Al to form Al2O3 sublayer at coating/scale interface, thereby leading to formation of Al-depleted zone in the coating below the Al2O3 sublayer. The corrosion resistance of the NiCrAlY coatings is attributed to the formation of the continuous and dense Al2O3 sublayer at the coating/scale interface, which acts as barrier to the migration of Cr to the surface. The appearance of Al3Y after 100 and 200 cycles also contributes to the increased corrosion resistance of coatings after 100 and 200 cycles. 相似文献