共查询到20条相似文献,搜索用时 30 毫秒
1.
R. Soltani T.W. Coyle J. Mostaghimi R.S. Lima C. Moreau 《Surface & coatings technology》2008,202(16):3954-3959
This article investigates the thermo-physical properties of plasma sprayed zirconia coatings produced by agglomerates of submicron size particles as the feedstock. The microstructure of these deposits is consisted of splats and non-molten particles. This bimodal structure generally shows a better performance than conventional coatings. The agglomerated feedstock with internal submicron size porosity may significantly affect porosity related properties, such as the thermal diffusivity. In this study different process parameters were used to deposit yttria stabilized zirconia coatings with conventional and bimodal structures. Results showed a good correlation between the shape and distribution of pores and thermal diffusivity of the coatings. 相似文献
2.
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
3.
《Acta Materialia》2001,49(11):1993-1999
Changes in processing parameters strongly affect the structure and properties of thermally sprayed coatings and, consequently, their performance. Residual stress in the deposits is a factor that needs consideration, since it has direct influence on the processability and integrity of the sprayed material. In order to enhance the understanding of this phenomenon, a study of measurements of residual stresses on a single particle level was undertaken. The deposit is built-up with the successive impingement of micron-sized droplet and therefore an understanding of the single splat microstructure and properties will provide a fundamental understanding of the underlying mechanisms. Residual stresses in thin coatings, as well as isolated particles—splats—deposited on stainless steel substrates were investigated using X-ray microdiffraction. Plasma sprayed molybdenum and cold sprayed copper were studied. The key process parameters considered were: in-flight particle energy and substrate temperature in the first case, and particle velocity in the latter. The results will be discussed with respect to the influence of each of these parameters, contribution of quenching and thermal stress component and splat formation. Further, the coating build-up from individual particles and the associated factors influencing residual stress will be discussed. 相似文献
4.
M. J. Kramer S. C. Okumus M. F. Besser Ö. Ünal M. Akinc 《Journal of Thermal Spray Technology》2000,9(1):90-94
Powders of Mo52Si38B10 were plasma sprayed under inert conditions onto stainless steel substrates to determine if high density free standing forms
could be synthesized by this process. Thermal spray conditions were varied to minimize porosity and oxygen impurities while
minimizing evaporative metal losses. The assprayed and sintered microstructures were characterized using scanning and transmission
electron microscopy and quantitative x-ray diffraction (XRD). The as-sprayed microstructure consisted of elongated splats
tens of microns in length and only one to three microns in thickness. The splats contained submicrometer grains of primarily
MoB and Mo5Si3B
x
(T1) and minor amounts of MoSi2 and a glassy grain boundary phase. The interior of the splats typically consisted of a fine eutectic of MoB and T1.
Small pieces were cut out of the cross section of the sample and pressureless sintered for 2, 6, and 10 h at 1800 °C in flowing
Ar. After sintering for 2 h at 1800 °C, the samples exhibited a coarser but equiaxed microstructure (1 to 5 μm grain size)
containing 78 vol.% T1, 16 vol.% MoB, and 6 vol.% MoSi2 as determined by XRD. Approximately 8 at.% of the Si formed silica. The high-temperature anneal removed all vestiges of the
layered structure observed in the as-sprayed samples. 相似文献
5.
Hua Xie Ying-Chun Xie Guan-Jun Yang Cheng-Xin Li Chang-Jiu Li 《Journal of Thermal Spray Technology》2013,22(8):1328-1336
Thermal spraying is one of the most important approaches for depositing thermally insulating ceramic top coatings for advanced gas turbines due to the low thermal conductivity of the coating resulting from its lamellar structure. The thermal conductivity of the coating has been explained based on the concept of thermal contact resistance and correlated to microstructural aspects such as splat bonding ratio, splat thickness, and the size of the bonded areas. However, the effect of intrasplat cracks on the thermal conductivity was usually neglected, despite the fact that intrasplat cracking is an intrinsic characteristic of thermally sprayed ceramic coatings. In this study, a model for the thermal conductivity of a thermally sprayed coating taking account of the effect of intrasplat cracks besides intersplat thermal contact resistance is proposed for further understanding of the thermal conduction behavior of thermally sprayed coatings. The effect of the intersplat bonding ratio on the thermal conductivity of the coating is examined by using the model. Results show that intrasplat cracks significantly decrease the thermal conductivity by cutting off some heat flux paths within individual splats. This leads to a deviation from the typical ideal thermal contact resistance model which presents cylindrical symmetry. Based on the modified model proposed in this study, the contribution of intrasplat cracks to the thermal resistivity can be estimated to be 42–57 % for a typical thermally sprayed ceramic coating. The results provide an additional approach to tailor the thermal conductivity of thermally sprayed coatings by controlling the coating microstructure. 相似文献
6.
热喷涂层由扁平粒子组成,呈层状结构。气孔不可避免地存在于涂层中,而这些气孔包括通常所指的微米级气孔以及亚微米级的气孔。亚微米级气孔由扁平粒子间的未结合界面和扁平陶瓷粒子内所产生的显微裂纹构成。业已开发成功陶瓷涂层的电镀技术,并利用电镀的钢在涂层断面上的分布,揭示热喷涂Al2O3涂层的的真实气孔结构的方法。该方法的最重要之处在于直观地揭示热喷涂层的扁平陶瓷粒子间的未结合界面。本论文将电镀技术应用于传统的等离子、低气压等离子以及爆炸喷涂法喷制的Al2O3涂层,用扁平粒子间平均结合率和扁平粒子的平均厚度为结构参数定量地评价涂层结构。考察热喷涂方法对扁平粒子间结合的影响。 相似文献
7.
An evaluation of microstructure-property relationship is important for thermally sprayed composite absorber coatings, because self-similarity in the microstructure is a key characteristic that can affect coating properties, such as flattened particle shape, pores, absorbent phase, and coating thickness. In this paper, a multiscale effective fractal model is reported to characterize the microstructure-property relationship for high-velocity oxygen fuel (HVOF) sprayed composite coatings. It shows the fractal of coating structure was presented to calculate the volume fraction of thermally sprayed absorber coatings with wavelet-fractal algorithm. As an example, the flattened particle shape, porosity, and thickness were researched for the microwave reflectivity coefficient of HVOF sprayed nanometer LBS (Li2O-B2O3-SiO2)-SiCβ composite coatings. The modeling approaches to establishing the relationships between coating microstructure and absorbing property was checked. 相似文献
8.
Thermally sprayed coatings are usually defined by their hardness, porosity, roughness, and wear resistance. Even though the Young’s modulus is an essential property, which describes the mechanical behavior of the coated components during their use, only few efforts have been made in the past to determine this property. The most common measurement methods of the Young’s modulus of thermally sprayed coatings are tensile tests, bending tests, and nanoindentations. During the tensile and bending tests a sliding of the splats can occur due to the laminar structure of the thermally sprayed coatings, influencing the measurement value. When using the nanoindentation test, only the elastic behavior of some splats can be determined because of a minimal measuring volume. However, the Young’s modulus of thermally sprayed coatings can also be determined by means of a resonant method, called impulse excitation technique. In this paper, the values of the Young’s moduli of thermally sprayed coatings, measured by several methods, are compared with each other and correlated to the microstructure of the coatings, investigated by means of scanning electron microscopy. 相似文献
9.
Thermally sprayed coatings are essentially layered materials, and lamellar interfaces are of great importance to coatings’ performances. In the present study, to investigate the microstructures and defect features at thermally sprayed coating interfaces, homoepitaxial 8 mol.% yttria-stabilized zirconia (YSZ) and heteroepitaxial lanthanum zirconia (LZ) films were fabricated. The epitaxial interfaces were examined by high-resolution transmission electron microscope (HR-TEM) in detail. As a result, we report, for the first time, an anomalous incommensurate homoepitaxial growth with mismatch-induced dislocations in thermally sprayed YSZ splats to create a homointerface. We also find the anomalous heteroepitaxial growth in thermally sprayed LZ splats. The mechanism of the anomalous incommensurate growth was analyzed in detail. Essentially, it is a pseudo-heteroepitaxy because of the lattice mismatch between the film and the locally heated substrate, as the locally heated substrate is significantly strained by its cold surroundings. Moreover, the super-high-density dislocations were found in the interfacial region, which resulted from sufficient thermal fluctuations and extremely rapid cooling rates. Both the anomalous lattice mismatch and super-high-density dislocations lead to weak interfaces and violent cracking in thermally sprayed coatings. These were also the essential differences between the conventional and the present epitaxy by thermal spray technique. 相似文献
10.
Thermal spray ceramic coatings deposited following the conventional routine exhibit a typical lamellar structure with a limited interface bonding ratio. The bonding between particles in the coating dominates coating properties and performance. In this review paper, the bonding formation at the interface between thin lamellae in the coating is examined. The effect of spray parameters on the bonding ratio is presented to reveal the main droplet parameters controlling bonding formation, which reveals that the temperature of the spray particle rather than its velocity dominates the bonding formation. The limitation to increase significantly the ceramic particle temperature inherent to the thermal spray process leads to the observation of a maximum bonding ratio of about 32%, while through controlling the surface temperature of the coating prior to molten droplet impact, the bonding at the lamellar interface can be significantly increased. Consequently, it is shown that with the proper selection of deposition conditions and control of the deposition temperature, the bonding ratio of ceramic deposits can be altered from a maximum of 32% for a conventional deposit to a maximum of 100%. Such wide adjustability of the lamellar bonding opens new possibilities for using thermal spray coatings in various applications requiring different microstructures and properties. The examination of recent studies shows that the bonding control makes it possible to fabricate porous deposits through surface-molten particles. Such an approach could be applied for the fabrication of porous materials, the deposition of high temperature abradable ceramic coatings, and for forming functional structured surfaces, such as a surface with super-hydrophobicity or a solid oxide fuel cell cathode interface with high specific surface area and high catalytic performance. Furthermore, complete interface bonding leads to crystalline structure control of individual splats through epitaxial grain growth. 相似文献
11.
G. Montavon S. Sampath C. C. Berndt H. Herman C. Coddet 《Journal of Thermal Spray Technology》1995,4(1):67-74
Several statistical tools (i.e., Gaussian and Weibull distribution analyses, the t-test, and analysis of the variance) were
used to examine relationships between vacuum plasma spray processing parameters and the morphology of flattened particles
(splats) on a smooth, polished substrate. Astroloy, a nickel-base powder, was vacuum plasma sprayed onto polished copper substrates
under various processing conditions. Different flattened particle shape factors, including equivalent diameter, elongation
factor, and degree of splashing, were determined using image analysis. The spray parameters (i.e., current intensity, chamber
pressure, argon mass flow rate, etc.) strongly influenced splat formation and morphology and thus deposit microstructure and
properties. 相似文献
12.
Particle deformation and cooling significantly affect the characteristics of thermally sprayed coatings, such as the adhesion and cohesion strength between a splat and a substrate and between splats, as well as the internal stresses of deposits. It is essential to understand these processes for the successful industrial application of thermal spray technology. However, to date, the microstructure of the boundary of a splat and the substrate has not been clarified, although much research has been conducted on splat formation and the cooling process. We have developed a microstructure model of the boundary between the splat and the substrate, based on splat morphology obtained from experiments. In the model, it is assumed that gaps, or voids, and contact areas are arranged on the splat boundary with the substrate in an orderly fashion. The model includes phase changes and heat resistance simulating the function of the microstructure during splat cooling. Assumptions in the model are that ambient gas trapped in the gaps, or voids, transfers heat only by conduction and not by convection or radiation. The results of the simulation indicated that the extent of gaps, or voids, significantly affects the rate of decrease of the average temperature of the splat surface, as well as the temperature distribution inside the splat. 相似文献
13.
Lin Chen Guan-Jun Yang Cheng-Xin Li Chang-Jiu Li 《Journal of Thermal Spray Technology》2016,25(5):959-970
Intrasplat cracks, an essential feature of thermally sprayed ceramic coatings, play important roles in determining coating properties. However, final intrasplat crack patterns are always considered to be disordered and irregular, resulting from random cracking during splat cooling, since the detailed formation process of intrasplat cracks has scarcely been considered. In the present study, the primary formation mechanism for intrasplat cracking was explored based on both experimental observations and mechanical analysis. The results show that the intrasplat crack pattern in thermally sprayed ceramic splats presents a hierarchical structure with four sides and six neighbors, indicating that intrasplat crack patterns arise from successive domain divisions due to sequential cracking during splat cooling. The driving forces for intrasplat cracking are discussed, and the experimental data quantitatively agree well with theoretical results. This will provide insight for further coating structure designs and tailoring by tuning of intrasplat cracks. 相似文献
14.
Guan-Jun Yang Chang-Jiu Li Cheng-Xin Li Katsuyoshi Kondoh Akira Ohmori 《Journal of Thermal Spray Technology》2013,22(1):36-47
The mechanical properties and related performance of thermally sprayed ceramic coatings are degraded by their relatively low adhesion and cohesion resulting from the limited bonding at substrate/splat interface and splat/splat interface. In this study, the influence of high strength adhesive infiltration on the microstructure and erosion performance of plasma-sprayed Al2O3 coatings was investigated to understand the improving mechanism of adhesion and cohesion through heterogeneous modification of nonbonded interfaces. Element distribution maps proved that the adhesive can be infiltrated from the coating surface to the coating/substrate interface through the inter-connected open pores including in-plane nonbonded area and microcracks in splats. Both adhesion and cohesion can be significantly improved by the heterogeneous modification of nonbonded lamellar interfaces of both splat/splat and splat/substrate through adhesive infiltration. The adhesive strength of the coating was increased from several MPa to ~50 MPa after adhesive infiltration. The erosion resistance at a large particle jet angle was improved by a factor of 3 due to the significant improvement of the lamellar cohesion, although the erosion resistance at a small particle jet angle was not significantly influenced. 相似文献
15.
In the plasma spray coating process, the coating’s profile and overall thickness are dependent on the number of overlapping
traverses of the torch, the shape of the particle spray plume, the spatial distribution of the in-flight parameters of the
particles within, and the orientation of the substrate. In this paper, a semi-empirical methodology for predicting three-dimensional
deposits by the plasma spray process is developed. It comprises of three stages: first, spatial distributions of the in-flight
parameters of multi-sized particles within the spray plume are determined by Computational Fluid Dynamics simulations. The
size and shape parameters of the splats formed when individual droplets impact and spread out are obtained by experiments.
Finally, a computer program is developed to integrate the particle parameters distribution and the empirical splat geometric
data to generate a three-dimensional profile representing the deposit. The procedures predict the deposition volumes and thicknesses
for different substrate inclinations with good agreement to experimentally sprayed deposits. 相似文献
16.
Lin Chen Guan-Jun Yang Cheng-Xin Li Chang-Jiu Li 《Journal of Thermal Spray Technology》2017,26(3):302-314
To explore the edge effect on intrasplat cracking of thermally sprayed ceramic splats, crack patterns of splats were experimentally observed and investigated through mechanical analysis. Both the polycrystalline splats and single-crystal splats showed obvious edge effects, i.e., preferential cracking orientation and differences in domain size between center fragments and edge fragments. In addition, substrate/interface delamination on the periphery was clearly observed for single-crystal splats. Mechanical analysis of edge effect was also carried out, and it was found that both singular normal stress in the substrate and huge peeling stress and shear stress at the interface were induced. Moreover, effective relief of tensile stress in splats is discussed. The good correspondence between experimental observations and mechanical analysis is elaborated. The edge effect can be used to tailor the pattern morphology and shed further light on coating structure design and optimization. 相似文献
17.
Mohand Amokrane Bradai Abdelaziz Ati Nedjemeddine Bounar 《Surface & coatings technology》2008,202(18):4538-4543
Thermally sprayed of 100Cr6 steel coatings are widely used to combat degradation of components and structures due to mechanical wear. In this paper, the microstructure and adhesion energy of 100Cr6 steel coatings thermally sprayed on a 35CrMo4 steel substrate are investigated. The microstructure characteristics of the deposits are studied using the combined techniques of X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM) including energy-dispersive spectroscopy (EDS). The practical work of adhesion of flame-sprayed 100Cr6 on steel substrate is determined using a four-point delamination bending test. The influence of a molybdenum bond coat on the adhesion is also studied. Microstructure suggests that the coating is mainly constructed by splats of γ-phase (fcc) and FeO. Phase analysis also confirms that during spraying process, a stable α-phase (bcc) was transformed into a new γ-phase (fcc). The highest values of the fracture energy are obtained for the 35CrMo4 substrate/100Cr6 steel deposit type samples. On the contrary, when a molybdenum bond coat is introduced (composite system 35CrMo4 substrate/Mo bond coat/100Cr6 steel deposit), the fracture energy decreases in a ratio of approximately three. So, the presence of a Mo bond coat as a barrier between the coating and the substrate has a negative role on the adhesion. 相似文献
18.
Salimijazi H. R. Coyle T. W. Mostaghimi J. Leblanc L. 《Journal of Thermal Spray Technology》2005,14(2):215-223
The microstructure, phase composition, and chemical composition of vacuum plasma-sprayed Ti-6Al-4V alloys were examined in
detail using a variety of techniques, including x-ray diffraction, x-ray photoelectron spectroscopy, and transmission electron
microscopy. The observed chemistry and structure were related to the conditions under which the deposit was formed and the
phase equilibria in the Ti alloy system. The porosity of the deposit was in the range of 3 to 5%. A slight decrease in the
Al content and a slight increase in the amount of oxygen and hydrogen was found relative to the starting powder. Within individual
splats, a columnar solidification structure can be seen. However, the as-deposited material is ≥90% α′ martensite that is
present in the form of fine lathes on the order of 500 nm in width surrounded by residual β-phase. This herringbone structure
obscures to some extent the preexisting columnar structure of the as-solidified β-phase. The material fails at low elongations
(∼1%) when tested in tension, with a macroscopic stress-strain curve, which appears to be quite brittle. Examination of the
fracture surface, however, reveals a ductile failure mode within individual splats, which is consistent with the structure
described above. Sections perpendicular to the fracture surface show that failure occurs at the weak splat boundaries through
the development and growth of voids between splats. 相似文献
19.
Quenching stress arises within a thermally sprayed splat as its thermal contraction after solidification is constrained by
the underlying solid. Dependence of the quenching stress in plasma-sprayed deposits of Ni-20Cr alloy and alumina on the substrate
temperature during spraying was discussed in conjunction with the change in the nature of the interlamellar contact between
splats. It was found by mercury intrusion porosimetry and observation of cross sections of impregnated deposits that the interlamellar
contact is improved significantly by raising the substrate temperature during deposition from 200 to 600 °C. The positive
dependence of the quenching stress on the substrate temperature in this temperature range was attributed to a stronger constraint
against thermal contraction of sprayed splats after solidification due to the improved contact. 相似文献
20.
L. Pawlowski 《Journal of Thermal Spray Technology》1996,5(3):317-334
This paper deals with the surfacing technology of ceramic anilox rolls. The rolls are used in the printing industry to transport
the precisely determined quantity of ink in the flexographic printing machines. The technology of roll surfacing is discussed
by taking the following aspects into account: preparation of the powder to spray the ceramic coating; thermal spraying of
the duplex (bond coating and ceramic top coating); postspray finishing by grinding and polishing; and laser engraving. The
powder used as the top coating of the aniloxes is chromium oxide. This powder might be prepared by such techniques as agglomeration,
fusing, and crushing, etc. The preparation technique influences coating properties, such as microstructure (tested with SEM,
OM, XRD, and XPS), open porosity, microhardness, and modulus of elasticity. Comparison of these properties enables optimum
powder preparation techniques to be found. APS technique is used to coat the anilox rolls. Optimization of the plasma spraying
parameters is discussed. Aniloxes are submitted to the grinding and polishing of the ceramic coating before laser engraving
occurs. The final roughness of the finished coating is discussed in view of an optimum absorption of the laser light energy
at engraving. Possible ways of reducing the spraying time are discussed, and future research toward improving the anilox roll
quality is proposed. 相似文献