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1.
The interdependence between plasma spray process parameters and porosity of YSZ coating microstructures was investigated with simultaneous consideration of the deposition efficiency. Based on a factorial experimental plan, the argon plasma gas flow, the current, the interaction of argon flow and current, and the spray distance for the Triplex II plasma gun were found to yield the main contributions to porosity as well as to deposition efficiency.Each of these three process parameters has a significant individual effect on the in-flight particle velocities and temperatures. The contribution to the effects on porosity arises almost exclusively from the particle temperature. Regarding the deposition efficiency, the larger contribution originates from the particle velocity.To achieve a targeted high porosity at reasonable deposition efficiency a simple linear regression model was applied yielding an argon flow of 50 slpm and a current of 470 A at a spray distance of 200 mm as the optimum parameter set. The average particle temperature estimated for this optimum is just above the melting temperature. At this setting, a porosity of 17.7% and a deposition efficiency of 32.5% may be expected.At a greater spray distance and lower power density (lower current and/or higher argon plasma gas flow) the deposition efficiency was observed to drop considerably. The cooling of the particles here becomes critical, i.e. the particles are only partly molten. This was verified by an analysis of the density distributions of measured in-flight particle temperatures. 相似文献
2.
A three-dimensional computational fluid dynamic (CFD) analysis using Fluent V5.4 was conducted on the in-flight particle behavior
during the plasma spraying process with external injection. The spray process was modeled as a steady jet issuing from the
torch nozzle via the heating of the are gas by an electric are within the nozzle. The stochastic discrete model was used for
the particle distribution. The particle temperature, velocity, and size inside the plasma plume at a specified standoff distance
have been investigated. The results show that carrier gas flow rate variation from 2 standard liters per minute (slm) to 4.0
slm can increase the centerline particle mean temperature and mean velocity by 10% and 16%, respectively, at the specified
standoff distance. A further increase of the carrier gas flow rate to 6 slm did not change the particle temperature, but the
particle velocity was decreased by 20%. It was also found that an increase in the total arc gas flow rate from 52 slm to 61
slm, with all other process parameters unchanged, resulted in a 17% higher particle velocity, but 6% lower particle temperature.
Some of these computational findings were experimentally confirmed by Kucuk et al. For a given process parameter setting,
the kinetic and thermal energy extracted by the particles reached a maximum for carrier gas flow rate of about 3.5–4.0 slm. 相似文献
3.
Taeyoung Han Zhibo Zhao Bryan A. Gillispie John R. Smith 《Journal of Thermal Spray Technology》2005,14(3):373-383
The kinetic spray coating process involves impingement of a substrate by particles of various material types at high velocities.
In the process, particles are injected into a supersonic gas stream and accelerated to high velocities. A coating forms when
the particles become plastically deformed and bond to the substrate and to one another upon collision with the substrate.
Coating formation by the kinetic spray process can be affected by a number of process parameters. In the current study, several
spray variables were investigated through computational modeling and experiments. The examined variables include the temperature
and pressure of the primary gas, the cross-sectional area of the nozzle throat, the nozzle standoff distance from a substrate,
and the surface condition of nozzle interior and the powder gas flow. Experimental verification on the effects of these variables
was performed primarily using relatively large-size aluminum particles (63–90 μm) as the feedstock material. It was observed
that the coating formation is largely controlled by two fundamental variables of the sprayed particles: particle velocity
and particle temperature. The effects of different spray conditions on coating formation by the kinetic spray process can
be generally interpreted through their influences on particle velocity and/or particle temperature. Though it is limited to
accelerate large particles to high velocities using compressed air or nitrogen as carrier gas, increasing particle temperature
provides an additional means that can effectively enhance coating formation by the kinetic spray process. 相似文献
4.
Characterization of Cold Spray Titanium Supersonic Jet 总被引:1,自引:0,他引:1
Titanium is widely used in aerospace, highly corrosive environments, and implants due to unique properties such as high strength
to weight ratio and excellent corrosion resistance. Cold gas dynamic spray (cold spray) technology, in contrast to current
fabrication technologies, has provided the potential for titanium to be utilized in broader industrial applications and at
lower cost. Particle velocity is the most important parameter in the cold spray process that leads to successful deposition
of titanium at supersonic speeds. In this study, particle image velocimetry (PIV) is utilized to characterize supersonic flow
field for a commercially pure (CP) titanium powder. The results represent experimentally determined velocity for titanium
particles under supersonic conditions with respect to propellant gas, spray temperature, and stagnation pressure. The high
velocity flow region outside of the cold spray nozzle was significantly extended using helium. An increase in stagnation temperature
results in a high velocity region close to the axis of the cold spray nozzle. In contrast, an increase in pressure expands
the high velocity regions in the cold spray plume. The PIV that is a whole-flow-field process is a practical characterization
technique for optimization of parameters and validation of the future models for the cold spray process. 相似文献
5.
Per Nylé Anita Hansbo Martin Friis Lars Pejryd 《Journal of Thermal Spray Technology》2001,10(2):359-366
Yttria stabilized ZrO2 particle in-flight characteristics in an Ar-H2 atmospheric plasma jet have been studied using analytical and experimental techniques. In the previous article,[1] the primary gas flow, plasma composition, current, and powder feed rate were systematically varied and particle surface temperatures,
velocities, and size distributions measured and statistically analyzed. In this paper, a mathematical model for the plasma
flow and particle characteristics is presented. Model predictions are compared with the experimental results in Ref 1 and
a reasonable correlation is found. A statistical investigation (composite cubic face (CCF)) is performed on the particle predictions,
giving fast and simple relationships between gun parameters and particle in-flight properties. The statistical and theoretical
models that are presented here combine to form a powerful and cost-effective tool, which can be used in the evaluation and
optimization of spray parameters off-line. 相似文献
6.
A general method to map and control thermal spray processes, ensuring predefined levels of selected final coating properties,
is presented. The method relies on monitoring and individually controlling particle velocity and particle temperature through
selected spray gun parameters. Mapping of the process results in process maps describing the individual effect of particle
velocity and particle temperature on each selected coating property of concern; in this case, different features of the microstructure
and deposition efficiency. From the information provided by the process maps, a process window is constructed. This process
window provides the limits within which particle velocity and particle temperature are allowed to vary to fulfill a predefined
coating specification. To verify the method, two predefined thermal barrier top coatings—one porous and one dense—were produced
by air plasma spray with satisfactory results. 相似文献
7.
The fluid and particle flow field characteristics of a high-velocity oxygen-fuel (HVOF) thermal spray (TS) system are analyzed
using a two-phase flow model and simulated using computational fluid dynamics (CFD) techniques. The model consists of a conservation
equation and constitutive relations for both gas and particle phases. Compressible, turbulent flow is modeled by ak-ɛ turbulent model. A Lagrangian formulation is used to model particle trajectory, and heat and momentum transfer. The fluid
velocity fluctuations resulting from gas turbulence are simulated by a stochastic model and the particle motion in the turbulent
flow is calculated in a Lagrangian Stochastic-Deterministic (LSD) method. Details of gas flow field, particle temperature
and particle velocity histories, and particle temperature and velocity profiles in the system are presented. For the validation
of the numerical analysis, the computed results are compared with available experimental measurement. Excellent agreement
between simulations and measurements is obtained for both gas and particle flow fields. A parametric study is also conducted
for different particle sizes and different nozzle barrel lengths. The flow phenomena for different flow parameters are analyzed
and explained as the result of gas dynamics and heat and momentum transfer between the two phases. The developed methodology
provides a means to analyze, design, and optimize the TS process. The numerical analysis presents a first comprehensive, fundamental
quantitative analysis for the HVOF TS system. 相似文献
8.
Optimization of Atmospheric Plasma Spray Process Parameters using a Design of Experiment for Alloy 625 coatings 总被引:2,自引:0,他引:2
Alloy 625 is a Ni-based superalloy which is often a good solution to surface engineering problems involving high temperature
corrosion, wear, and thermal degradation. Coatings of alloy 625 can be efficiently deposited by thermal spray methods such
as Air Plasma Spraying. As in all thermal spray processes, the final properties of the coatings are determined by the spraying
parameters. In the present study, a D-optimal experimental design was used to characterize the effects of the APS process
parameters on in-flight particle temperature and velocity, and on the oxide content and porosity in the coatings. These results
were used to create an empirical model to predict the optimum deposition conditions. A second set of coatings was then deposited
to test the model predictions. The optimum spraying conditions produced a coating with less than 4% oxide and less than 2.5%
porosity. The process parameters which exhibited the most important effects directly on the oxide content in the coating were
particle size, spray distance, and Ar flow rate. The parameters with the largest effects directly on porosity were spray distance,
particle size, and current. The particle size, current, and Ar flow rate have an influence on particle velocity and temperature
but spray distance did not have a significant effect on either of those characteristics. Thus, knowledge of the in-flight
particle characteristics alone was not sufficient to control the final microstructure. The oxidation index and the melting index incorporate all the parameters that were found to be significant in the statistical analyses and correlate well with the
measured oxide content and porosity in the coatings.
相似文献
F. AzarmiEmail: |
9.
采用超音速等离子喷涂可低成本、高效率制备钛涂层。采用响应曲面法(RSM)中的Box-Behnken(BBD)设计分析了Ar流量、功率、喷涂距离3个因素与超音速等离子射流中钛粒子飞行速度和温度的交互性,利用SEM和显微硬度计研究了钛涂层的微观结构和显微硬度。结果表明:建立的线性模型可靠,喷涂距离对粒子飞行速度和温度影响最大,且随喷涂距离增加粒子飞行速度减小温度增加,而Ar流量和功率对粒子飞行速度和温度的影响与喷涂距离相反。超音速等离子喷涂制备出的钛涂层硬度较低,且呈多孔结构,随粒子飞行速度增加孔隙率降低。 相似文献
10.
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
11.
An analysis of a low temperature high velocity air fuel (LTHVAF) thermal spray process is presented using computational fluid
dynamics (CFD). The originality of the process lies in the injection of liquid (water) upstream of the powder injection to
control to gas temperature and, therefore, the heat transfer to the injected particles. First, computation fluid dynamic techniques
are implemented to solve the mass, momentum, and energy conservation equations in the gas phase. A turbulence model based
on the renormalized group theory (RNG) is used for the turbulent flow field. The gas dynamic data are, then, used to model
the behavior of the liquid droplets and particles in the gas flow field. The calculated results show that the liquid flow
rate should range between 20 and 30 kg/h to achieve the optimal gas characteristics for particle treatment. They also show
that particle velocity and temperature are strongly affected by particle size. At the gun exit, the particle velocity and
temperature range between 700 and 300 m/s and between 900 and 400 K, respectively, for Cu and Ni particles with size distributions
of 1 to 50 μm. As expected, the smaller particles have higher velocity and temperature. The metal coatings (Nickel and copper)
produced by the LTHVAF spray process are characterized by low oxide content, low residual stresses, high deposition rates,
and good bonding to the substrate. 相似文献
12.
真空度对真空冷喷涂气固两相流的影响 总被引:1,自引:1,他引:0
目的真空度直接影响着真空冷喷涂时气体流动特性和颗粒撞击速度,研究真空度对气体和颗粒流动特性的影响。方法确定真空冷喷涂系统结构,采用FLUENT软件进行真空冷喷涂气固两相流研究,通过数值模拟研究真空度对流场和颗粒撞击速度的影响,并研究相同压力比下的气固两相流特性。结果当入口压力一定时,喷管内的气体轴线速度、密度和温度与环境压力大小无关;而在射流区,环境压力越小,则气体轴线速度波动越小、密度越低,但到达基板后的气体温度均接近喷管入口温度。环境压力对大粒径颗粒的撞击速度影响较大,颗粒撞击速度随环境压力增大而先增后减,最佳环境压力可根据气相云图和气体密度来确定。当进出口压力比相同时,喷管内和射流区域内的气相速度云图基本相同,气体轴线速度曲线基本重合,而基板前的颗粒速度不同,此时环境压力越低,颗粒速度越高,越有利于形成涂层。结论采用计算流体动力学分析方法厘清了真空度对真空冷喷涂气固两相流的影响,为涂层制备奠定了理论基础。 相似文献
13.
In cold spraying, bonding is associated with shear instabilities caused by high strain rate deformation during the impact.
It is well known that bonding occurs when the impact velocity of an impacting particle exceeds a critical value. This critical
velocity depends not only on the type of spray material, but also on the powder quality, the particle size, and the particle
impact temperature. Up to now, optimization of cold spraying mainly focused on increasing the particle velocity. The new approach
presented in this contribution demonstrates capabilities to reduce critical velocities by well-tuned powder sizes and particle
impact temperatures. A newly designed temperature control unit was implemented to a conventional cold spray system and various
spray experiments with different powder size cuts were performed to verify results from calculations. Microstructures and
mechanical strength of coatings demonstrate that the coating quality can be significantly improved by using well-tuned powder
sizes and higher process gas temperatures. The presented optimization strategy, using copper as an example, can be transferred
to a variety of spray materials and thus, should boost the development of the cold spray technology with respect to the coating
quality.
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
14.
A real-time, nonintrusive measurement technique was successfully applied to a Tafa Model 9000 (TAFA Incorporated, Concord,
NH) twin wire electric arc thermal spray system to simultaneously measure particle size, velocity, and temperature within
the spray plume. Aluminum wire was sprayed with the current varied from 100 to 300 amp, and the gun pressure (air flowrate)
varied from 40 to 75 psia. For all cases, the average sizes of the molten aluminum particles along the spray centerline range
from 33 to 53 μm. The particles accelerate to peak velocities between 130 and 190 m/s, then decelerate slightly as they travel
downstream. The average centerline particle temperature ranges from 2004 to 2056 °C, and the temperature profile remains fairly
flat throughout transport to the substrate. A stagnation pressure probe was used to quantify the gas flow regime in the unladen
jet. The wires were found to have a pronounced effect on the flow, resulting in a complex three-dimensional flowfield with
mixed regions of subsonic and supersonic flow. 相似文献
15.
To better understand the plasma spray coating process, an experimental study of the interaction between a subsonic thermal
plasma jet and injected nickel- aluminum particles was performed. The velocity, temperature, and composition of the argon/helium
gas flow field was mapped using an enthalpy probe/mass spectrometer system. The sprayed particle flow field was examined by
simultaneously measuring the size, velocity, and temperature of individual particles. Particle and gas temperatures were compared
at the nominal substrate stand- off distance and axially along the median particle trajectory. Temperature and velocity differences
between the particle and the gas surrounding it are shown to vary substantially depending on the trajectory of the particles.
On the median trajectory, the average particle is transferring heat and momentum back to the plasma by the time it reaches
the substrate. Because the exchange of heat and momentum is highly dependent on the particle residence time in the core of
the plasma, the condition of particles at the substrate can be optimized by controlling the particle trajectory through the
plasma. 相似文献
16.
The influences of the dimensions of optical components and the trajectories of spray particles on the variations of the waveforms
of the radiation signals from the spray particles were studied both theoretically and experimentally for correct simultaneous
measurement of the particle parameters including particle velocity, surface temperature, size, and spatial distribution. Two
types of filtering masks, including single-windowed and dual-windowed, were used as models in the current study. The evolution
of the radiation pulse from a moving thermal spray particle was simulated through the change of the projected area of the
particle image spot on the filtering mask window. The experimental detection of the thermal radiation pulses was performed
for the high velocity oxygen fuel (HVOF) process using an optoelectronic measurement system.
The theoretical simulation clearly showed that the characteristic waveforms of the thermal radiation signals from the spray
particles are varied with the distance and orientation of the trajectories of thermal spray particles with respect to the
ideal image plane of the filtering window plane. The typical variations of the characteristic waveforms obtained theoretically
have been observed experimentally with HVOF spraying. The waveforms expected theoretically were correlated well with those
observed experimentally.
The characteristic waveforms of the radiation signals from the spray particles in a trapezoid shape with a saturated top platform
contain the information for spray particle parameters including velocity, surface temperature, size, and spatial distribution.
With the dual-windowed filtering mask, the particle velocity can be correctly measured with the bi-peak radiation signal in
triangle-like shape, and the surface temperature may be estimated reasonably. However, the particle size cannot be estimated
correctly. It was revealed that the characteristics of the waveforms were remarkably influenced by the image spot size. Therefore,
the expansion of the image spot based on the relation between the image spot size of an in-flight particle and optical lens
parameters obtained optically was discussed. The influence of the image spot size on the waveform characteristics was examined. 相似文献
17.
J. F. Bisson C. Moreau M. Dorfman C. Dambra J. Mallon 《Journal of Thermal Spray Technology》2005,14(1):85-90
The influence of secondary hydrogen and current on the deposition efficiency (DE) and microstructure of yttria-stabilized
zirconia (YSZ) coatings was evaluated. To better understand the influence of the spray process on coating consistency, a YSZ
powder, −125 +44 μm, was sprayed with nitrogen/hydrogen parameters and a 9 MB plasma gun from Sulzer Metco. DE and coating
porosity, which were produced using two different spray gun conditions yielding the same input power, were compared. Amperage
was allowed to vary between 500 and 560 A, and hydrogen was adjusted to maintain constant power, while nitrogen flow was kept
at a fixed level. Several power conditions, ranging from 32 to 39 kW, were tested. Different injection geometries (i.e., radial
with and without a backward component) were also compared. The latter was found to produce higher in-flight temperatures due
to a longer residence time of the powder particles in the hotter portion of the plasma. Porosity was based on cross-sectional
micrographs. In-flight particle temperature and velocity measurements were also carried out with a special sensor for each
condition. Test results showed that DE and coating density could vary significantly when a different hydrogen flow rate was
used to maintain constant input power. On the other hand, DE was found to correlate very well with the temperature of the
in-flight particles. Therefore, to obtain more consistent and reproducible DE and microstructures, it is preferable to maintain
the in-flight particle temperature around a constant value instead of keeping a constant input power by adjusting the secondary
hydrogen flow rate. 相似文献
18.
介绍了一种新型大气等离子喷涂方法,该方法采用特殊内通道结构的直流非转移电弧等离子发生器,可以直接在大气条件下获得长度100~1000 mm之间变化的等离子射流。在大气条件下,等离子射流的流动特性具有"长、直、准"的层流或类层流状态,工作时噪音小于80 dB。在工作参数范围内,等离子射流的长度在固定总气流量条件下可以随输出功率的增加而增长;射流的长度在固定输出功率的条件下随总气流量的增加而减小。当使用在大气等离子喷涂技术中时,会为飞行粉末颗粒带来超长的加热和加速过程。文中详细介绍了大气层流等离子喷涂技术的研究历史和研究现状,以及研究团队利用该新型技术制备的6种涂层的显微结构、颗粒的飞行和加热特点,并对比了目前其他大气等离子喷涂技术的结果。结果表明,文中介绍的方法在最低的输出功率和气流量条件下,为金属和陶瓷颗粒提供了超长的飞行和加热条件,表现为较低的颗粒飞行速度和超高的颗粒表面温度。可以在不同的射流长度或喷涂距离下,获得不同的颗粒熔化状态或涂层结构,并发现可以直接在大气条件下获得大规模气液共沉积的涂层。 相似文献
19.
Effect of processing conditions on porosity formation in cold gas dynamic spraying of copper 总被引:1,自引:0,他引:1
Saden H. Zahiri Darren Fraser Stefan Gulizia Mahnaz Jahedi 《Journal of Thermal Spray Technology》2006,15(3):422-430
The cold gas dynamics process is a promising low-temperature spray process in which particles are accelerated in a supersonic
flow before impacting with substrate to be coated. In this study the effect of spray temperature, spray pressure, and particle
size on porosity formation in cold spray coatings are investigated. Results show that an increase in spray temperature and
a decrease in particle size lead to a decline in volume fraction of porosity. Furthermore, particle velocity and particle
temperature are determined to be the significant parameters for elimination of porosity. A model is proposed for estimation
of the volume fraction of porosity for alloy of this study. 相似文献
20.
Using laser anemometry, laser fluxmetry, and statistical two-color pyrometry, the velocity, number flux, and surface temperature
distributions of alumina and zirconia particles in dc plasma jets have been determined inflight for various spraying parameters.
The flux measurements emphasized the importance of the carrier gas flow rate, which must be adjusted to the plasma jet momentum
depending on the arc current, nozzle diameter, gas flow rate, and gas nature. It has also been shown that the particle trajectories
depend both on the particle size and injection velocity distributions and that the position and tilting of the injector plays
a great role. The particle size drastically influences its surface temperature and velocity, and for the refractory materials
studied, only the particles below 45 μm in diameter are fully molten in Ar-H2 (30 vol%) plasma jets at 40 kW. The morphology of the particles is also a critical parameter. The agglomerated particles
partially explode upon penetration into the jet, and the heat propagation phenomenon is seriously enhanced, particularly for
particles larger than 40 μm. The effects of the arc current and gas flow rate have been studied, and the results obtained
in an air atmosphere cannot be understood without considering the enhanced pumping of air when the plasma velocity is increased.
The Ar-He (60 vol%) and Ar-H2 (30 vol%) plasma jets, when conditions are found where both plasma jets have about the same dimensions, do not result in
the same treatment for the particles. The particles are not as well heated in the Ar-He jet compared to the Ar-H2 jet. Where the surrounding atmosphere is pure argon instead of air (in a controlled atmosphere chamber), he radial velocity
and temperature distributions are broadened, and if the velocities are about the same, the temperatures are higher. The use
of nozzle shields delays the air pumping and increases both the velocity and surface temperature of the particles. However,
the velocity increase in this case does not seem to be an advantage for coating properties. 相似文献