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1.
This paper presents an investigation of the influence of plasma spray process conditions on the in-flight particle behavior
and their cumulative deposition to form a coating on the substrate. Three-dimensional computational fluid dynamics (CFD) analyses
were performed to model the in-flight particle behavior in the plasma-spray process and their deposition on the substrate.
The plasma spray was modeled as a jet issuing from the torch nozzle through the electrical heating of the arc gas. In the
model, particles were injected into the plasma jet where they acquired heat and momentum from the plasma, some got melted
and droplets were formed. By means of a droplet splatting model, the particle in-flight data generated by the CFD analyses
were further processed to build up an imaginary three-dimensional deposition profile on a flat stationary substrate. It is
found that the powder carrier gas flow rate influences the particle distribution on the substrate by imparting an injection
momentum to the particles that were directed radially into the plasma jet in a direction perpendicular to the plasma jet.
The larger sized particles will acquire higher injection momentum compared with the smaller sized particles. This causes particle
distribution at the substrate surface that is elliptical in shape with the major axis of ellipse parallel to the particle
injection port axis as illustrated in Fig. 1. Larger particles tend to congregate at the lower part of the ellipse, due to
their greater momentum. The distribution of particle size, temperature, velocity, and count distribution at the substrate
was analyzed. Further, based on the size and the computed particle temperature, velocity histories, and the impact sites on
the substrate, the data were processed to build up a deposition profile with the Pasandideh-Fard model. The shapes of deposition
profiles were found to be strongly driven by the segregation effect. 相似文献
2.
Effect of Ceramic Particle Velocity on Cold Spray Deposition of Metal-Ceramic Coatings 总被引:1,自引:0,他引:1
A. Sova V. F. Kosarev A. Papyrin I. Smurov 《Journal of Thermal Spray Technology》2011,20(1-2):285-291
In this paper, metal-ceramic coatings are cold sprayed taking into account the spray parameters of both metal and ceramic particles. The effect of the ceramic particle velocity on the process of metal-ceramic coating formation and the coating properties is analyzed. Copper and aluminum powders are used as metal components. Two fractions of aluminum oxide and silicon carbide are sprayed in the tests. The ceramic particle velocity is varied by the particle injection into different zones of the gas flow: the subsonic and supersonic parts of the nozzle and the free jet after the nozzle exit. The experiments demonstrated the importance of the ceramic particle velocity for the stability of the process: Ceramic particles accelerated to a high enough velocity penetrate into the coating, while low-velocity ceramic particles rebound from its surface. 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.
ExplanationofsymbolsaThermaldiffusivityCdHeatcapacityofmeltD.ParticlediameterhHeattransfercoefficientNcNusseltnumberPrPrandtlnumberrRadicaldirectioncoordinateRParticleradiusRoinitialparticleradiusReReynoldsnumberTBMeltbulktemperatureTinMeltfreezingpointTmlParticlemeltingpointToInitialparticletemperaturet.Timeneededformeltingofcrustt,.TimeforparticlebeginningtomeltinthecaseoftheparticlemeltingtemperaturelowerthanthatofmeltfreezingVParticleslipvelocityAHLatentheatofsolidificationofme… 相似文献
5.
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
6.
M. Faizan-Ur-Rab S. H. Zahiri P. C. King C. Busch S. H. Masood M. Jahedi R. Nagarajah S. Gulizia 《Journal of Thermal Spray Technology》2017,26(8):1874-1887
Cold spray is a solid-state rapid deposition technology in which metal powder is accelerated to supersonic speeds within a de Laval nozzle and then impacts onto the surface of a substrate. It is possible for cold spray to build thick structures, thus providing an opportunity for melt-less additive manufacturing. Image analysis of particle impact location and focused ion beam dissection of individual particles were utilized to validate a 3D multicomponent model of cold spray. Impact locations obtained using the 3D model were found to be in close agreement with the empirical data. Moreover, the 3D model revealed the particles’ velocity and temperature just before impact—parameters which are paramount for developing a full understanding of the deposition process. Further, it was found that the temperature and velocity variations in large-size particles before impact were far less than for the small-size particles. Therefore, an optimal particle temperature and velocity were identified, which gave the highest deformation after impact. The trajectory of the particles from the injection point to the moment of deposition in relation to propellant gas is visualized. This detailed information is expected to assist with the optimization of the deposition process, contributing to improved mechanical properties for additively manufactured cold spray titanium parts. 相似文献
7.
指出吹气法制备泡沫铝的单炉发泡工艺必定会有熔体剩余,并进行了实验验证。建立了单炉发泡工艺中颗粒含量和吹气深度的微分方程,其边界条件就是泡沫的稳定判据公式。对含公称直径9μm Al2O3颗粒的两个A356铝合金发泡过程进行了计算,并与实验值比较。结果表明:计算时,尽管由于将颗粒直径和吸附系数取为定值,使计算存在误差,但结论仍然合理可信;为减少单炉发泡过程的熔体剩余,应该提高颗粒含量和初始吹气深度,减小颗粒尺寸和临界覆盖率。 相似文献
8.
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
9.
ZrOCl_2-Al体系熔体反应生成Al_3Zr_((p)),Al_2O_(3(p))/Al复合材料的反应机制 总被引:1,自引:0,他引:1
利用X射线衍射仪 (XRD)和扫描电子显微镜 (SEM ) ,对ZrOCl2 Al体系熔体反应生成的复合材料组织进行了分析 ,结果表明 :ZrOCl2 Al体系反应生成相为Al3 Zr和α Al2 O3 ,颗粒尺寸为 0 .2~ 5 μm ,形状以多面体为主 ;随反应起始温度升高 ,生成的颗粒体积分数增大 ,熔体温度也升高 ,但当熔体温度高于 12 0 0℃时 ,Al3 Zr出现聚集、长大。提出了ZrOCl2 Al体系的反应是气液反应和固液反应的复合过程 ,建立了ZrOCl2 /Al反应中的控制环节ZrO2 /Al反应的动力学模型及化学反应速率的关系式。 相似文献
10.
The prefabricated Al/TiC alloy with high TiC particle content was prepared by XD^TM process,The uniform distribution process of TiC particles in the stationary zinc melt was studied and analyzed using self-made experimental equipment,and the model of the uniform distribution process was built.The results show that zinc diffuses into the prepared Al/TiC alloy after it is placed in the zinc melt at temperatures below the melting point of aluminum,which leads to the decrease of the liquidus temperature of Al-Zn alloy in the surface layer of Al/TiC alloy.When the liquidus temperature of Al-Zn alloy is equal to or below the temperature of zinc melt,Al-Zn alloy melts and TiC particles drop with it from the Al/TiC alloy and then transfer into the zinc melt and finally distribute uniformly in it. 相似文献
11.
The influence of powder particle injection velocity on the microstructure of coatings consisting of an Al-Si matrix reinforced with SiC particles prepared by laser cladding from mixtures of powders of Al-12 wt.% Si alloy and SiC was investigated both experimentally and by modeling. At low injection velocities SiC particles react with the molten aluminum alloy. Only a small fraction of SiC remains in the microstructure, which contains large amounts of particles of the reaction products Al4SiC4 and Si dispersed in the α-Al + Si eutectic matrix. By contrast, at high injection velocities chemical reactions between SiC and molten aluminum are almost entirely suppressed and the resulting microstructure consists only of SiC particles dispersed in the matrix. To investigate whether this behavior could be explained by the different temperatures reached by the injected particles as they fly through the laser beam, a physical-mathematical model describing the interaction between the laser beam and the powder stream in the off-axis blown powder laser cladding process was developed and applied to calculate the temperature attained by the powder particles as a result of their interaction with an Nd:YAG laser beam (λ = 1.06 µm). At an injection velocity of 1 m/s the maximum temperature attained by SiC and Al-12Si particles is 3150 and 180 ºC, respectively. This result demonstrates that particle injection velocity is a major parameter affecting the microstructure of coatings produced by laser cladding, and must be carefully controlled. 相似文献
12.
Effect of Substrate Temperature on Deposition Behavior of Copper Particles on Substrate Surfaces in the Cold Spray Process 总被引:2,自引:0,他引:2
M. Fukumoto H. Wada K. Tanabe M. Yamada E. Yamaguchi A. Niwa M. Sugimoto M. Izawa 《Journal of Thermal Spray Technology》2007,16(5-6):643-650
The deposition behavior of sprayed individual metallic particles on the substrate surface in the cold spray process was fundamentally
investigated. As a preliminary experiment, pure copper (Cu) particles were sprayed on mirror-polished stainless steel and
aluminum (Al) alloy substrate surfaces. Process parameters that changed systematically were particle diameter, working gas,
gas pressure, gas temperature, and substrate temperature, and the effect of these parameters on the flattening or adhesive
behavior of an individual particle was precisely investigated. Deposition ratio on the substrate surface was also evaluated
using these parameters. From the results obtained, it was quite noticeable that the higher substrate temperature brought about
a higher deposition rate of Cu particles, even under the condition where particles were kept at room temperature. This tendency
was promoted more effectively using helium instead of air or nitrogen as a working gas. Both higher velocity and temperature
of the particles sprayed are the necessary conditions for the higher deposition ratio in the cold spraying. However, instead
of particle heating, substrate heating may bring about the equivalent effect for particle deposition.
This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been
expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain
Montavon, Ed., ASM International, Materials Park, OH, 2007. 相似文献
13.
Effect of Substrate Temperature on the Formation Mechanism of Cold-Sprayed Aluminum, Zinc and Tin Coatings 总被引:4,自引:0,他引:4
When describing the cold-spray process, one of the most widely used concepts is the critical velocity. Current models predicting
critical velocities take the temperature of the sprayed particles explicitly into account, but not the surface temperature
(substrate or already deposited layers) on which the particle impacts. This surface temperature is expected to play an important
role, since the deformation process leading to particle bonding and coating formation takes place both on the particle and
the substrate side. The aim of this work is to investigate the effect of the substrate temperature on the coating formation
process. Experiments were performed using aluminum, zinc, and tin powders as coating materials. These materials have a rather
large difference in critical velocities that gives the possibility to cover a broad range of deposition velocity to critical
velocity ratio using commercial low-pressure cold-spray system. The sample surface was heated and the temperature was varied
from room temperature to a high fraction of the melting point of the coating material for all three materials. The change
in temperature of the substrate during the deposition process was measured by means of a high speed IR camera. The coating
formation was investigated as a function of (1) the measured surface temperature of the substrate during deposition, (2) the
gun transverse speed, and (3) the particle velocity. Both single particle impact samples and thick coatings were produced
and characterized. Both the particle-substrate and interparticle bonding were evaluated by scanning electron microscopy (SEM)
and confocal microscopy.
This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been
expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain
Montavon, Ed., ASM International, Materials Park, OH, 2007. 相似文献
14.
It has been demonstrated recently that intensive melt shearing can be an effective approach to the grain refinement of both shape casting and continuous casting of Mg alloys. In the present study, the mechanisms of grain refinement by intensive melt shearing were investigated through a combination of both modelling and experimental approaches. The measurement of the cooling curves during solidification, quantification of grain size of the solidified samples, and image analysis of the MgO particle size and size distribution in the pressurized filtration samples were performed for the AZ91 alloy with and without intensive melt shearing. The experimental results were then used as input parameters for the free growth model to investigate the mechanisms of grain refinement by intensive melt shearing. The experimental results showed that, although intensive melt shearing does not change the nucleation starting temperature, it increases the nucleation finishing temperature, giving rise to a reduced nucleation undercooling. The theoretical modelling using the free growth model revealed quantitatively that intensive melt shearing can effectively disperse MgO particles densely populated in the oxide films into more individual particles in the alloy melt, resulting in an increase in the MgO particle density by three orders of magnitude and the density of active nucleating MgO particles by a factor of 20 compared with those of the non-sheared melt. Therefore, the grain refining effect of intensive melt shearing can be confidently attributed to the significantly increased refining efficiency of the naturally occurring MgO particles in the alloy melt as potent nucleation sites. 相似文献
15.
Lin Zhu Tien-Chien Jen Yen-Ting Pan Hong-Sheng Chen 《Journal of Thermal Spray Technology》2017,26(8):1859-1873
Cold gas dynamic spray (CGDS) is a surface coating process that uses highly accelerated particles to form the surface coating. In the CGDS process, metal particles with a diameter of 1-50 µm are carried by a gas stream at high pressure (typically 20-30 atm) through a de Laval-type nozzle to achieve supersonic velocity upon impact onto the substrate. Typically, the impact velocity ranges between 300 and 1200 m/s in the CGDS process. When the particle is accelerated to its critical velocity, which is defined as the minimum in-flight velocity at which it can deposit on the substrate, adiabatic shear instabilities will occur. Herein, to ascertain the critical velocities of different particle sizes on the bonding efficiency in CGDS process, three-dimensional numerical simulations of single particle deposition process were performed. In the CGDS process, one of the most important parameters which determine the bonding strength with the substrate is particle impact temperature. It is hypothesized that the particle will bond to the substrate when the particle’s impacting velocity surpasses the critical velocity, at which the interface can achieve 60% of the melting temperature of the particle material (Ref 1, 2). Therefore, critical velocity should be a main parameter on the coating quality. Note that the particle critical velocity is determined not only by its size, but also by its material properties. This study numerically investigates the critical velocity for the particle deposition process in CGDS. In the present numerical analysis, copper (Cu) was chosen as particle material and aluminum (Al) as substrate material. The impacting velocities were selected between 300 and 800 m/s increasing in steps of 100 m/s. The simulation result reveals temporal and spatial interfacial temperature distribution and deformation between particle(s) and substrate. Finally, a comparison is carried out between the computed results and experimental data. 相似文献
16.
W. Trompetter M. Hyland D. McGrouther P. Munroe A. Markwitz 《Journal of Thermal Spray Technology》2010,19(5):1024-1031
The effect of substrate surface oxides on splat-substrate bonding was investigated by thermally spraying NiCr particles onto
aluminum substrates with surface oxide layers grown hydrothermally and electrochemically. Cross sections of bonded solid and
molten splats revealed substantial deformation of both the substrate and the surface oxide. In spite of the substantial substrate
deformation, there was no significant loss of the surface oxide material and there was no observed diffusion of the substrate
oxide into the NiCr particle or vice versa. For solid splats, the substrate oxide was still present over the entire splat-substrate
interface, however for molten splats, the oxide had been penetrated in several locations allowing close proximity of the splat
metal to the substrate metal. These results strengthen the theory that oxide layers impede bonding and that successful bonding
occurs only when the surface oxide is substantially deformed or disrupted to produce mechanically interlocking features at
the interface. 相似文献
17.
Aiguo Liu Mianhuan Guo Hailong Hu 《Journal of Materials Engineering and Performance》2010,19(6):848-851
Surface of a low carbon steel Q235 substrate was melted by a plasma torch, and tungsten carbide (WC) particles were injected
into the melt pool. WC reinforced surface metal matrix composite (MMC) was synthesized. Dry sliding wear behavior of the surface
MMC was studied and compared with the substrate. The results show that dry sliding wear resistance of low carbon steel can
be greatly improved by plasma melt injection of WC particles. Hardness of the surface MMC is much higher than that of the
substrate. The high hardness lowers the adhesion and abrasion of the surface MMC, and also the friction coefficient of it.
The oxides formed in the sliding process also help to lower the friction coefficient. In this way, the dry sliding wear resistance
of the surface MMC is greatly improved. 相似文献
18.
A novel two step mixing method including injection of particles into the melt by inert gas and stirring was used to prepare aluminum matrix composites (AMCs) reinforced with Al2O3 particles. Different mass fractions of micro alumina particles were injected into the melt under stirring speed of 300 r/min. Then the samples were extruded with ratios of 1.77 or 1.56. The microstructure observation showed that application of the injection and extrusion processes led to a uniform distribution of particles in the matrix. The density measurements showed that the porosity in the composites increased with increasing the mass fraction of Al2O3 and stirring speed and decreased by extrusion process. Hardness, yield and ultimate tensile strengths of the extruded composites increased with increasing the particle mass fraction to 7%, while for the composites without extrusion they increased with particle mass fraction to 5%. 相似文献
19.
Real time close-up images of in-flight particles plasma sprayed onto a substrate and in freestream condition (without substrate
present) are captured. Besides the images, particle behavior in terms of temperature, velocity, and heading are measured by
the Spray Watch particle imaging diagnostics system. The monitoring and measurement of particle behavior have been performed
for substrates inclined at various angles to investigate the effect of the substrate on particle behavior. The close-up images
show that particles propelled from the torch travel with high momentum and are not affected by the substrate and inclination
angle. Quantitative analyses of the particle average velocity and heading data with and without the different inclined substrates
also lead to similar conclusions. The particle velocity is resolved into tangential and normal velocity components parallel
and perdendicular to the substrate, respectively. The tangential velocity component controls the degree of splat elongation
into elliptical shape from the circular shape seen in perpendicular impact. This is of practical importance in industrial
spraying of engineering components of complex curvatures. A higher tangential velocity component also implies that more powders
are lost through rebounding and overspraying and thus reducing the deposition efficiency. The normal velocity component decreases
when substrate inclination increases, which tends to weaken the coating adherence. 相似文献
20.
Eui Hyuk Kwon Sung Ho Cho Jeong Whan Han Chang Hee Lee Hyung Jun Kim 《Metals and Materials International》2005,11(5):377-381
The cold spray process is a relatively new process that uses high velocity metallic particles for surface modifications. Metallic
powder particles are injected into a converging-diverging nozzle and accelerated to supersonic velocities. In this study two-dimensional
temperature and velocitiy distributions of gas along the nozzle axis are calculated and the effects of gas pressure and temperature
on particle velocities and temperature inside and outside the nozzle are investigated. It was found that acceleration of the
gas velocity takes place in the area of the nozzle throat, and it increases and reaches a maximum value at the nozzle exit.
Due to compression shocks, irregular changes of the gas jet properties were found in the area after the nozzle and these resulted
in the experience of the maximum particle velocity by the change of the particle size at a given gas pressure and temperature. 相似文献