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1.
The fracture toughness of plasma-sprayed Al2O3 coatings in terms of critical strain energy release rate G
Ic was investigated using a tapered double cantilever beam (TDCB) approach. This approach makes the fracture toughness be measured
only using the critical fracture load disregarding crack length during test. The Al2O3 coatings were deposited under different spray distances and plasma powers to clarify the effect of spray parameters on the
G
Ic of the coatings. The fracture surfaces were examined using scanning electron microscope. On the basis of an idealized layer
microstructure model for thermal sprayed coatings, the theoretical relationship between the cohesive fracture toughness and
microstructure is proposed. The correlation between the calculated fracture toughness and observed value is examined. It was
found that the fracture toughness of plasma sprayed Al2O3 coatings is not significantly influenced by spray distance up to 110 mm, and further increase in spray distance to 130 mm
resulted in large decrease in the fracture toughness of the coatings. The G
Ic value predicted based on the proposed model using lamellar interface mean bonding ratio and the effective surface energy
of bulk ceramics agreed well with the observed G
Ic data. Such agreement evidently shows that the fracture toughness of thermally sprayed ceramic coatings at the direction along
coating surface is determined by lamellar interface bonding. 相似文献
2.
Robert B. Heimann 《Journal of Thermal Spray Technology》2011,20(4):898-908
Surface roughness strongly controls essential properties of thermally sprayed wear- and corrosion-resistant coatings including
their mechanical adhesion to the substrate, tribological performance, efficient retention of lubricating materials, and also
the presence of sufficient carrying surface able to support the wear couple along the line of contact expressed by the Abbott-Firestone
curve. The determination of the surface fractal geometry may yield useful information on the topography of plasma-sprayed
coatings beyond that provided by a single roughness parameter such as R
a or R
z. The fractal geometry of atmospheric plasma-sprayed chromium oxide coatings, deposited according to two different statistical
experimental design protocols, was assessed through determination of the Hurst exponent H of fractal Brownian motion (fBM),
as well as the area-scaled fractal complexity (ASFC) obtained by triangular tessellation (“patchwork” method). Attempts were
made to correlate fractality with coating adhesion strength. 相似文献
3.
Thermally sprayed molybdenum coatings are used in a variety of industrial applications, such as auto-motive piston rings,
aeroturbine engines, and paper and plastics processing machinery. Molybdenum ex-hibits excellent scuffing resistance under
sliding contact conditions. However, plasma-sprayed molybde-num coatings are relatively soft and require dispersion strengthening
(e.g., Mo2C) or addition of a second phase (e.g., NiCrBSi) to improve hardness, wear resistance, and thus coating performance. In this
study, Mo-Mo2C composite powders were plasma sprayed onto mild steel substrates. Considerable decarburi-zation was observed during air
plasma spraying—a beneficial condition because carbon acts as a sacrifi-cial getter for the oxygen, thereby reducing the oxide
content in the coating. Finer powders showed a greater degree of decarburization due to the increased surface area; however,
the starting carbide con-tent in the powder exerted very little influence on the extent of decarburization. The friction properties
of Mo-Mo2C coatings were significantly improved compared to those of pure molybdenum under con-tinuous sliding contact conditions.
It also was found that the abrasion resistance of the coatings improved with increasing carbide addition. 相似文献
4.
The study aimed at characterizing mechanical properties of TiO2 coatings obtained by the use of aqueous suspensions of fine rutile and anatase particles onto metal substrates. Thickness of the coatings was found with the use of optical microscope observations of metallographical cross-sections. The coatings morphology was found with scanning electron microscope (SEM) and their phase composition was determined by X-ray diffraction method. The mechanical properties were characterized using scratch test. The test enabled to characterize the adhesion of coatings by determination of critical force necessary to peel off the coatings from the substrate and, on the other hand, to estimate their cohesion by the measurement of the scratch hardness. The hardness was calculated using the width of the scratch and the value of force applied. The design of experiments (DOE) of spraying with the use of a 23 full factorial plan was applied to rutile powder. The coatings were sprayed onto aluminium substrate. The DOE enabled to find the effects of three principal parameters, i.e. electric power input to plasma, spray distance and suspension feed rate onto coating adhesion expressed by critical force. A preliminary data for anatase powder sprayed with one set of operational parameters onto stainless steel substrate are also shown. 相似文献
5.
In the present study Ni−18Cr−6Al, Ni−22Cr−10Al−1Y and TiAlO composite powders were coated on Ti−6Al−4V substrates by atmospheric
plasma spraying, and the coated specimens were evaluated by isothermal and cyclic oxidation resistance tests at 800°C. The
oxidation kinetics of the plasma sprayed NiCrAl, NiCrAlY, and TiAlO composite coated specimens obey a parabolic rate law.
The oxidation resistance of the plasma sprayed NiCrAl and NiCrAlY coatings is superior to that of plasma sprayed TiAlO composite
coating. The best oxidation resistance was observed in the plasma sprayed NiCrAlY coatings. This is mainly attributed to the
formation of Y−Al−O complex oxides and Ni3Al with higher thermal stability on the coatings. 相似文献
6.
Investigations of tantalum coatings on steel by vacuum plasma spraying In this work the possibilities of the production of tantalum coatings by vacuum plasma spraying were investigated. Suitable parameters of the vacuum plasma spraying process were determined, and the quality of vacuum plasma sprayed tantalum coatings was evaluated with regard to chemical composition, adhesion strength, density and corrosion behaviour. To obtain high-quality coatings it was necessary to apply sufficient plasma power as well as an optimal injection of spraying powder into the plasma torch. A complete melting of the tantalum powder particles could not he achieved. The coatings obtained showed a good adhesion strength but a low formability (ductility). The corrosion resistance against HCL and HNO3 was evaluated by curves of the current density versus potential. With the aid of the passive current density it was determined that the corrosion resistance of the sprayed coatings was not as excellent as of compact tantalum. The increased surface roughness was not significant with respect to the corrosion behaviour. The reduced corrosion resistance could be caused probably by a high oxygen content of the tantalum powder, especially by oxides around individual powder particles. In contrast to tantalum, vacuum plasma sprayed titanium coatings showed the same corrosion resistance as compact titanium under the same testing conditions. 相似文献
7.
A premixture of elemental powders of titanium and aluminum was supplied as a spray material for the direct fabrication of
titanium aluminide matrixin situ composites by means of reactive low-pressure plasma spraying with a nitrogen and hydrogen mixed plasma gas. The aluminum
content varied from 10 to 63 wt.% in the premixtures. The matrix of sprayed layers consisted of three kinds of titanium aluminides—Ti3A1, TiAl, and TiAl3—which begin to form on a low-carbon steel substrate immediately after deposition. The formation of nitrides, which act as
a reinforcement, occurs both during the flight of liquid droplets and on the substrate. The nitrogen content is approximately
4 to 5 wt.% in the sprayed intermetallic matrix composites, regardless of the aluminum content of the premixtures. The kinds
of titanium aluminides andin situ nitrides developed depend on the aluminum content of the premixtures. The homogeneity of the distribution of aluminum and
titanium in sprayed intermetallic matrix composites has been improved by vacuum annealing. The predominant TiAl phase that
formed in the sprayed intermetallic matrix composites with a Ti-36 wt.% AI premixture increases in quantity through annealing.
Although some minor nitrides disappear through annealing, the principal reinforcement, Ti2AlN, does not decompose, but increases in quantity. The hardness of sprayed intermetallic matrix composites varies with aluminum
content of the premixtures, but is always greater than that of sprayed titanium aluminides containing no nitrides. Annealing
does not reduce the hardness of sprayed intermetallic matrix composites. Sprayed and annealed intermetallic matrix composites
with a Ti-36 wt.% Al premixture maintain their hardness of approximately 500 HV up to 800 K. Hence, reactive low-pressure
plasma spraying offers a promising fabrication method for titanium aluminide matrixin situ composites, which are expected to excel in wear resistance applications at elevated temperatures. 相似文献
8.
The structure, hardness, and shear adhesion strength have been investigated for Cr3C2-NiCr cermet coatings sprayed onto a mild steel substrate by 200 kW high power plasma spraying (HPS) and high velocity oxy-fuel
(HVOF) processes. Amorphous and supersaturated nickel phases form in both as-sprayed coatings. The hardness of the HVOF coating
is higher than that of the HPS coating, because the HVOF coating contains more nonmelted Cr3C2 carbide particles. On heat treating at 873 K, the amorphous phase decomposes and the supersaturated nickel phase precipitates
Cr3C2 carbides so that the hardness increases in the HPS coating.
The hardness measured under a great load exhibits lower values compared with that measured with a small load because of cracks
generated from the indentation. The ratio of the hardnesses measured with different loads can be regarded as an index indicating
the coating ductility. The ductility of the HVOF coating is higher than that of the HPS coating. Adhesion strength of the
HVOF coating was high compared with the HPS coating. The adhesion of the coatings is enhanced by heat treating at 1073 K,
and that of the HVOF coating is over 350 MPa. 相似文献
9.
10.
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
11.
Arjun Dey Anoop K. Mukhopadhyay S. Gangadharan Mithilesh K. Sinha Debabrata Basu 《Journal of Thermal Spray Technology》2009,18(4):578-592
Microplasma sprayed (MIPS) HAP coatings on SS316L substrates were characterized by x-ray diffraction, Fourier transformed
infrared spectroscopy, optical microscopy, scanning electron microscopy (SEM), field emission scanning electron microscopy
(FE-SEM), atomic force microscopy and image analysis. The coating showed a high degree of crystallinity ~92%, a high porosity
level of 20 vol.% and a moderate bonding strength of about 13 MPa. The displacement controlled three-point bend tests and
associated results of optical microscopy indicated that crack deflection, crack branching, and also local crack bridging occurred
during crack propagation in the coating. The nano-hardness (H) and Young’s modulus (E) of the MIPS-HAP coatings as measured by nanoindentation technique were about 6 and 92 GPa, respectively. The fracture toughness
(K
ic) of the coating was ~0.6 MPa·m0.5. From the nano-scratch experiments, the critical normal load at which localized microcracking led to delamination was measured
to be ~400 mN. 相似文献
12.
The wear resistance of plasma sprayed molybdenum blend coatings applicable to synchronizer rings or piston rings was investigated
in this study. Four spray powders, one of which was pure molybdenum and the others blended powders of bronze and aluminum-silicon
alloy powders mixed with molybdenum powders, were sprayed on a low-carbon steel substrate by atmospheric plasma spraying.
Microstructural analysis of the coatings showed that the phases formed during spraying were relatively homogeneously distributed
in the molybdenum matrix. The wear test results revealed that the wear rate of all the coatings increased with increasing
wear load and that the blended coatings exhibited better wear resistance than the pure molybdenum coating, although the hardness
was lower. In the pure molybdenum coatings, splats were readily fractured, or cracks were initiated between splats under high
wear loads, thereby leading to the decrease in wear resistance. On the other hand, the molybdenum coating blended with bronze
and aluminum-silicon alloy powders exhibited excellent wear resistance because hard phases such as CuAl2 and Cu9Al4 formed inside the coating. 相似文献
13.
A comparative study of tribological behavior of plasma and D-gun sprayed coatings under different wear modes 总被引:3,自引:0,他引:3
Sundararajan G. Prasad K. U. M. Rao D. S. Joshi S. V. 《Journal of Materials Engineering and Performance》1998,7(3):343-351
In recent years, thermal sprayed protective coatings have gained widespread acceptance for a variety of industrial applications.
A vast majority of these applications involve the use of thermal sprayed coatings to combat wear. While plasma spraying is
the most versatile variant of all the thermal spray processes, the detonation gun (D-gun) coatings have been a novelty until
recently because of their proprietary nature. The present study is aimed at comparing the tribological behavior of coatings
deposited using the two above techniques by focusing on some popular coating materials that are widely adopted for wear resistant
applications, namely, WC-12% Co, A12O3, and Cr3C2-MCr.
To enable a comprehensive comparison of the above indicated thermal spray techniques as well as coating materials, the deposited
coatings were extensively characterized employing microstructural evaluation, microhardness measurements, and XRD analysis
for phase constitution. The behavior of these coatings under different wear modes was also evaluated by determining their
tribological performance when subjected to solid particle erosion tests, rubber wheel sand abrasion tests, and pin-on-disk
sliding wear tests. The results from the above tests are discussed here. It is evident that the D-gun sprayed coatings consistently
exhibit denser microstructures and higher hardness values than their plasma sprayed counterparts. The D-gun coatings are also
found to unfailingly exhibit superior tribological performance superior to the corresponding plasma sprayed coatings in all
wear tests. Among all the coating materials studied, D-gun sprayed WC-12%Co, in general, yields the best performance under
different modes of wear, whereas plasma sprayed Al2O3 shows least wear resistance to every wear mode. 相似文献
14.
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
15.
D. Zois A. Lekatou M. Vardavoulias I. Panagiotopoulos A. Vazdirvanidis 《Journal of Thermal Spray Technology》2008,17(5-6):887-894
Nanostructured and conventional Al2O3 powders have been plasma sprayed to produce coatings. The parameters for retaining a fraction of the nanostructure were investigated. Dissimilarities were observed between the two types of coating, regarding properties and phase proportions, which are related with the different percentages of semimolten particles in the coatings. The nanocoatings retained a higher percentage of semimolten particles than the conventional coatings owing to the higher porosity of the nanoparticle agglomerates. The molten part of both conventional and nanostructured coatings consisted of γ-Al2O3 of columnar morphology. In order to investigate the mechanism of the melting front advance into the particle interior, the particles were sprayed directly into deionized water. The nanoparticles mainly formed hollow spheres, whereas the conventional particles mainly formed compact spheres. The internal porosity of the solidified nanoparticle agglomerates, which affected the overall coating porosity and, consequently, coating properties such as hardness, adhesion, and surface roughness, was linked to the hollow sphere phenomenon. 相似文献
16.
This paper summarizes the basic results of fatigue testing of bodies with both metallic and ceramic thermally sprayed coatings.
Three kinds of ceramic coatings (Al2O3, Cr2O3, and olivine) sprayed with DC plasma under identical conditions were investigated together with metallic Ni-5wt.%Al coatings
sprayed by wire arc, DC plasma, and HVOF. The elastic modulus of the deposited coatings was investigated using four point
bending and resonance method. Bending fatigue tests at resonance frequency were performed with cantilever beam specimens.
The processes taking place during the fatigue test are identified and discussed. The morphology of the fracture surfaces was
investigated together with microstructure and porosity of the coatings. 相似文献
17.
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
18.
Particle size effects on chemistry and structure of Al-Cu-Fe quasicrystalline coatings 总被引:1,自引:0,他引:1
Gas atomized Al63Cu25Fe12 powders of varying size fractions were plasma sprayed onto hot (~600 °C) and cool (~25 °C) substrates using Mach I and subsonic
plasma gun configurations. The chemical composition and phase contents of coatings were determined. Furthermore, coatings
were annealed in vacuum at 700 °C for 2 h to observe phase changes. It was found that finer particles (e.g., <25 μm) tend
to vaporize Al during spraying, which shifts the coating composition away from the quasicrystalline (ψ) single-phase region
in the Al-Cu-Fe phase diagram. Coatings deposited on hot substrates were denser, richer in theψ phase, and harder than the
corresponding coatings deposited onto cool substrates. 相似文献
19.
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
20.
Jo Ann Gan Christopher C. Berndt Yat Choy Wong James Wang 《Journal of Thermal Spray Technology》2013,22(2-3):337-344
Formation of voids is inevitable in plasma sprayed coatings and the role of voids on coating properties has long been established. In fact, the void content within coatings is adjusted by optimizing the process parameters to obtain coatings with desirable performance. Quantification of voids via image analysis allows determination of not only the void content within a coating, but also the spatial distribution of the voids. Void content in plasma sprayed neodymium iron boron (Nd-Fe-B) coatings was adjusted by changing the standoff distance, and was found to vary from 1.8 to 8.2%. Spatial distribution parameters, which include nearest neighbor distance (d min), mean near neighbor distance (d mean), and nearest neighbor angle (θn), were determined via the Dirichlet tessellation method. Coefficient of variation (COV) values of d min and d mean allow determination of inhomogeneity and degree of clustering of the voids within a coating. The θn values reveal the anisotropic behavior of voids within plasma sprayed coatings. The influence of void content and its spatial distribution within the coatings on the microhardness and elastic modulus of coatings was determined. 相似文献