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1.
Parametric study of an HVOF process for the deposition of nanostructured WC-Co coatings 总被引:1,自引:1,他引:1
Bartuli Cecilia Valente Teodoro Cipri Fabio Bemporad Edoardo Tului Mario 《Journal of Thermal Spray Technology》2005,14(2):187-195
Nanocrystalline WC-Co coatings were deposited by high velocity oxyfuel from commercial nanostructured composite powders. Processing
parameters were optimized for maximal retention of the nanocrystalline size and for minimal decarburation of the ceramic reinforcement.
Thermochemical and gas-dynamical properties of gas and particle flows within the combustion flame were identified in various
operating conditions by computational fluid-dynamics (CFD) simulation. Significant improvements of the mechanical properties
of the coatings were obtained: a decrease of the friction coefficient was measured for the nanostructured coatings, together
with an increase of microhardness and fracture toughness. 相似文献
2.
The principles underlying composite material behavior during metallographic preparation of coating cross-sections are generally
not well understood. This study of the effect of extended fine polishing on apparent porosity shows that adequate polishing
times, using a fine abrasive (3 μm) and low force, are required to remove prior deformation in the section surface and to
reveal the true porosity of the underlying composite material. Insufficient polishing times can result in considerable underestimation
of porosity. A model is described which proposes that the deformation induced in the material during grinding and polishing,
even at low applied force, results in smearing of material into voids that exist in the plane of the section. 相似文献
3.
选用4种不同WC尺度的WC-12Co粉末作为初始喂料,通过超音速火焰喷涂系统(HVOF)制备了涂层。考察了不同粉末结构对涂层沉积过程的脱碳行为和涂层组织性能的影响。结果表明:WC颗粒尺寸减小加剧了涂层脱碳行为,涂层中W2C含量增加,粘结相非晶化现象明显,涂层硬度增加,但是当WC颗粒尺寸减小到纳米尺度时,韧性下降。双峰结构涂层表现出最好的韧性同时兼备较高的硬度。 相似文献
4.
Initiation and early growth of fatigue cracks of a medium carbon steel with HVOF thermally sprayed WC-Co coatings prepared
from two types of commercially available powders with similar total chemical composition were investigated under rotating
bending conditions.
The morphology of the fatigue crack is divided into two type—linear cracks and net-like cracks—depending on the types of powders
and the thickness of the coatings. The fatigue cracks in thinner coatings were closer to each other than those for the thick
coatings. 相似文献
5.
The corrosion resistance of NiCrBSi coating deposited on steel substrate by HVOF was examined using electrochemical tests and immersion tests so as to offer an experimental basis to expand a promising applied field of HVOF in aqueous medium, comparing with those of coatings deposited by oxyacetylene flame spraying and flame cladding. The results show that the general corrosion rate of HVOF sprayed coatings is quite bigger than that of clad coatings, bat it is less sensitive to local corrosion. There is less and smaller porosity in the coatings deposited by HVOF than that in flame sprayed coatinlgs. The effects of porosity on the corrosion current density was indistinctive, bat the existence of large amount of defects in the coatings damaged the cohesion of the coatings, causing the metallic particles drop off from the coatings under the influence of corrosive medium. Improving the quality and reducing the porosity of coatings is the key to get the coatings with high corrosion resistance. 相似文献
6.
Alfredo Valarezo Giovanni Bolelli Sanjay Sampath Luca Lusvarghi 《Surface & coatings technology》2010,205(7):2197-2208
In this paper, effective damage tolerance of a functionally graded coating (FGC) deposited by high velocity oxygen fuel (HVOF) spraying is observed. The thick FGC (≈ 1.2 mm) consists of 6 layers with a stepwise change in composition from 100 vol.% ductile AISI316 stainless steel (bottom layer) to 100 vol.% hard WC-12Co (top layer) deposited onto an AISI316 stainless steel substrate. Damage tolerance is observed via 1) an increase in compliance with depth, and 2) an increase in fracture resistance by containment, arrest and deflection of cracks. A smooth gradation in the composition and hardness through the coating thickness is found by scanning electron microscopy and depth-sensing microindentation, respectively. The in-situ curvature measurement technique reveals that during the deposition of the FGC, compressive stresses exist in the lower, metallic layers owing to peening effect of successive impact, and these gradually evolve to high tensile, in the top layers. Tensile stresses appear to be due to quenching alone; thermal stresses are low because of the gradation. All of this is beneficial for the deposition of a thick coating.The FGC structure shows the ability to reduce cracking with increased compliance in the top layer during static and dynamic normal contact loading, while retaining excellent sliding wear resistance (ball-on-disk tests). Results are discussed in comparison to the behavior and properties of coatings of similar individual compositions and thicknesses, as well as a thick monolithic WC-12Co sprayed coating. Further improvements in the processing are proposed to enhance the adhesion strength and avoid coating delamination under high load contact-fatigue conditions. 相似文献
7.
Pornthep Chivavibul Makoto Watanabe Seiji Kuroda M. Komatsu 《Surface & coatings technology》2008,202(21):5127-5135
A great concern to save the amount of tungsten carbide used in various mechanical components has become important because of an increase of global demand and the resultant sharp rise in the price in recent years. Sintered tungsten carbide (WC) tools are usually used in woodworking industry because of their excellent combination of hardness and toughness. However, the actual area necessary for cutting is very small compared to the overall cutting tool body. In this work, three high-velocity oxy-fuel (HVOF) sprayed WC-Co coatings with different carbide size (0.2, 2, and 6 µm) on high speed tool steel substrates were fabricated and then grinded to produce cutting tools. Characterization of the deposited coating was done by scanning electron microscope, X-ray diffraction, hardness and indentation fracture toughness tests. The wood machining tests were performed on natural wood (Apitong) and medium density fiberboard (MDF) to study their performance as a cutting tool. The results showed that the hardness values of the coatings were approximately the same as that of sintered material, while the fracture toughness values were significantly lower. The wood machining tests on Apitong revealed that the coating tools were worn by the same level of edge recession as the sintered material. However, they showed numerous edge chippings over the worn surfaces and the level of edge chipping tended to increase with reducing the carbide size. The wood machining tests on MDF revealed that the coating tools were worn by the same level of edge recession in the low density wear zone as the sintered material but by a significantly higher level in the high density wear zone. 相似文献
8.
9.
Corrosion mechanism of NiCrBSi coatings deposited by HVOF 总被引:2,自引:0,他引:2
Wei-Min Zhao Yong Wang Li-Xian Dong Kai-Yuan Wu Jin Xue 《Surface & coatings technology》2005,190(2-3):293-298
NiCrBSi alloy powders were coated on a low carbon steel substrate using high-velocity oxygen fuel (HVOF) thermal spraying, and corrosion tests were carried out by immersing the specimens in 3.5% NaCl with pH adjusted to 3 by addition of acetic acid. Techniques such as scanning electron microscope (SEM), spectral analysis, electron probe microanalysis (EPMA) and X-ray diffraction (XRD) were employed to study the mechanistic process of corrosion of the coating surface. It was found that the corrosion of the NiCrBSi coating first occurred around the particles that had not melted during spraying and the defects such as pores, inclusions and microcracks, then followed by the development along the paths formed by pores, microcracks and lamellar structure, resulting in exfoliation or laminar peeling off. Adjusting the thermal spraying parameters to reduce the electrochemical unevenness or sealing the pores can improve the corrosion resistance of the coating. 相似文献
10.
Investigation of the residual stresses and microstructural properties associated with HVOF thermal spray coating of WC-17 wt% Co of same thickness on three substrates with coefficients of thermal expansion different to that of WC. The residual stresses were measured by X-ray diffraction sin2ψ techniques using CoKα radiation. The results indicated residual stresses that have different natures for the as-sprayed coatings despite using the same powder as feedstock. The magnitudes of the stresses in the as-sprayed condition are low. 相似文献
11.
The aircraft hookpoint used for an arrested landing is exposed to various forms of heavy wear and impact. Nowhere is this
more true than training field landings, where the hookpoint is subjected to drag along a concrete runway for possibly thousands
of feet while flying at high speeds and heavy downloads. After extensive screening, a series of materials were subjected to
special impact tests and concrete wear tests. Ten coatings, applied by thermal spray, were selected for future arrestment
testing on the basis of these results. 相似文献
12.
13.
采用超音速火焰喷涂方法(HVOF)在304不锈钢基体表面制备WC和WC-12Co的复合涂层WC-Co,研究亚微米WC的添加对涂层相组成、显微硬度、耐磨性能和表面形貌的影响。利用X射线衍射、压痕法、往复式摩擦磨损实验和扫描电子显微镜(SEM)分别对涂层的相组成、显微硬度、磨损性能和表面形貌进行分析测试,并分析涂层的磨损过程和机制。结果表明,添加质量分数5%的亚微米WC颗粒显著提高了涂层的显微硬度(16.3%);增强了涂层的耐磨性,磨损率从6.09×10-7 mm3/Nm减小到5.15×10-7 mm3/Nm(减小13.8%);亚微米WC颗粒喷涂后在涂层中保持了WC相,并主要存在于WC-Co扁平粒子界面和孔隙。基于涂层中扁平粒子的结合特性与磨损失效特征,建立强化模型,分析亚微米WC颗粒对涂层扁平粒子界面的强化机制。 相似文献
14.
In the context of the European project ‘Coatings for Supercritical Steam Cycles’ (SUPERCOAT), the use of steam oxidation resistant coatings on currently available ferritic materials with high creep strength but poor oxidation resistance was investigated in order to allow increase in the operating temperature of steam power plants from 550 to 650 °C. Among the explored coating techniques for this application, chosen on the basis of being potentially appropriate for coating steam turbine components, High Velocity Oxy Fuel (HVOF) thermal spray has resulted in one of the most successful techniques. Different alloyed materials such as FeCrAl, NiCrSiFeB, FeAl, NiCr and FeCr have been deposited, optimized and tested under flowing steam at 650 °C. Characterization of as deposited and tested samples by metallography, SEM‐EDS and XRD was carried out. Some of these coatings form protective pure chromium or aluminium oxides exhibiting excellent behaviour for at least 15 000 h of exposure, whereas others form less stable complex mixed oxides which nevertheless grow at considerably slower rates than the oxides formed on uncoated P92 (9 wt% Cr ferritic steel). 相似文献
15.
There has been an increase in interest of late regarding the properties of thermally sprayed WC-Co cermets with nanograin
carbide particles. These powders have shown interesting properties in sintered components, giving high values of hardness
(2200–2300 VHN) and improved wear properties. The method used for the processing for these materials—solution formation, spray
drying and chemical conversion, rather than introduction of WC as solid particles to a molten binder—allows the formation
of sub-100 nm WC particles as a hard second phase.
The work presented here examined the effect of composition on the microstructure and wear properties of some nanostructured
WC-Co materials. WC-Co cermets with 8, 10, 12, and 15% Co binder phase were deposited using a Sulzer Metco hybrid DJ HVOF
thermal spray system. Optimization of deposition conditions was necessary because of the unique morphology of the powders
(thick-shelled hollow spheres) to produce dense consolidated deposits.
There is a higher degree of decarburization of the WC phase in the nanostructured materials compared with the conventional
WC-Co. This dissolution of the hard phase is also noted to increase on decreasing binder phase content.
The nanostructured WC-Co coatings have a lower wear resistance compared with the conventional WC-Co for abrasive wear and
small particle erosion. The abrasive wear resistance of these nanostructured materials was found to increase on decreasing
cobalt binder content. This trend in abrasive wear resistance is consistent with studies on conventional sized cermets and
is believed to be more dependent upon proportion of binder phase content than degree of decarburization for the materials
studied. The small particle erosion resistance of the nanostructured coatings was found to increase on increasing cobalt content. 相似文献
16.
Wear and erosion behavior of plasma-sprayed WC-Co coatings 总被引:3,自引:0,他引:3
Wear mechanisms of air plasma-sprayed WC-12%Co coatings were studied by using a dry sand rubber wheel (DSRW) abrasive, ring-on-square
adhesive wear, and alumina particle erosion tests. Coating properties such as intersplat cohesive strength, porosity, surface
roughness, hardness, and retained carbide as well as microstructures were characterized to assess their relationship on wear
performance. Porosity, hardness, surface roughness, and retained carbide of the coatings are not the principal factors affecting
wear performance. Intersplat cohesive strength of coatings, measured by a simple bonding test, is the most significant factor
that relates to the wear rate of thermal spray coatings. 相似文献
17.
Chromium carbide/nickel chromium coatings obtained by the high- velocity oxyfuel thermal spray proc-ess were characterized
using conventional and high- resolution microscopy to identify the complex micro-structure that results from this thermal
spraying technique. Thermal cycling and long isothermal treatment were studied, as were the adhesion properties of as- coated
and thermally treated samples. 相似文献
18.
Powder/processing/structure relationships in WC-Co thermal spray coatings: A review of the published literature 总被引:5,自引:0,他引:5
H. L. de Villiers Lovelock 《Journal of Thermal Spray Technology》1998,7(3):357-373
Thermally sprayed coatings based on tungsten carbide are widely used but not yet fully understood, particularly with regard
to the chemical, microstructural, and phase changes that occur during spraying and their influence on properties such as wear
resistance. The available literature on thermally sprayed WC-Co coatings is considerable, but it is generally difficult to
synthesize all of the findings to obtain a comprehensive understanding of the subject. This is due to the many different starting
powders, spray system types, spray parameters, and other variables that influence the coating structures and cause difficulties
when comparing results from different workers.
The purpose of this review is to identify broad trends in the powder/processing/structure relationships of WC-Co coatings,
classified according to powder type and spray method. Detailed comparisons of coating microstructures, powder phase compositions
and coating phase compositions as reported by different researchers are given in tabular form and discussed. The emphasis
is on the phase changes that occur during spraying. This review concerns only WC-12% Co and WC-17% Co coatings, and contrasts
the coatings obtained from the cast and crushed, sintered and crushed, and agglomerated and densified powder types. Properties
such as hardness, wear, or corrosion resistance are not reviewed here. 相似文献
19.
Manish Roy 《Journal of Thermal Spray Technology》2002,11(3):393-399
The objective of the present work was to determine the dynamic hardness of WC-Co coatings from the dynamic hardness of the
coating substrate system. It was also the purpose of this work to evaluate the influence of coating composition, coating thickness,
and substrate materials on the dynamic hardness of the coating. To achieve the above-mentioned objectives, WC-12%Co and WC-17%Co
coatings were deposited by detonation spraying on three different substrate materials: mild steel, commercially pure (CP)
aluminum, and CP titanium. The dynamic hardness of the coating/substrate composite was evaluated by a drop weight system.
The dynamic hardness of the coating independent of the substrate was determined from the dynamic hardness of the coating/substrate
composite. 相似文献
20.
J.G. La Barbera-Sosa Y.Y. Santana D. Chicot J. Caro E.S. Puchi-Cabrera 《Surface & coatings technology》2008,202(18):4552-4559
The present work has been conducted in order to determine the microstructural features, hardness and elastic modulus of two different Ni-base coatings deposited by means of HVOF thermal spray, onto a SAE 1045 plain carbon steel substrate. The morphology and chemical composition of the phases that are present in the coatings were characterized by means of SEM, EDS and XRD techniques. Image analysis was used for the evaluation of the coatings porosity. Both conventional and instrumented indentation tests were also carried out on the surface and cross section of the coatings, in order to evaluate the effect of coating microstructure on hardness and elastic modulus. Conventional indentation tests were conducted using a Knoop indenter and a maximum load of 9.8 N. Instrumented indentation tests, in which the indenter depth and applied load were recorded continuously, were carried out employing a Vickers indenter and maximum loads of 0.49, 0.98, 1.96, 4.9 and 9.8 N. Instrumented nanoindentation tests (in a continuous stiffness measurement mode) were also conducted employing a Berkovich indenter with a maximum load of 9.8 N. The elastic modulus was computed by means of the Oliver and Pharr method and compared with the values determined by means of the method earlier advanced by Marshall et al. The results obtained indicate that the elastic modulus values determined on the cross section of the coatings are higher than those obtained on the surface, clearly indicating the anisotropy of the structure. Also, the values found employing a Berkovich indenter are very similar to those derived by means of the Vickers indenter. In addition, the these values are in agreement with those determined by taking into consideration the elastic recovery of the short Knoop diagonal after removal of the load. 相似文献