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1.
Nanocrystalline Al−Mg coatings were produced using the cold gas dynamic-spraying technique. Unsieved Al−Mg powder of average
nanocrystalline grain size in the range of 10 to 30 nm and with a particle size distribution from 10 to >100 μm was used as
the feedstock powder. The resulting coatings were evaluated using scanning electron microscopy (SEM), transmission electron
microscopy, as well as microhardness and nanoindentation measurements. Coating observations suggest that the wide particle
size distribution of the feedstock powder has a detrimental effect on the coating quality but that it can be successfully
mitigated by optimizing the spraying parameters. Nanohardness values close to 3.6 GPa were observed in both the feedstock
powder and coatings, suggesting the absence of cold-working hardening effects during the process. The effects of the substrate
surface roughness and thickness on coating quality were investigated. The deposited mass measurements performed on the coatings
showed that the effect of using different grit sizes for the substrate preparation is limited to small changes in the deposition
efficiency of only the first few layers of deposited material. The SEM observation showed that the substrate surface roughness
has no significant effect on the macrostructures and microstructures of the coating. The ability to use the cold gas dynamic
spraying process to produce coatings on thin parts without noticeable substrate damage and with the same quality as coatings
produced on thicker substrates was demonstrated in this work.
The original version of this paper was published in the CD ROM Thermal Spray Connects: Explore Its Surfacing Potential, International Thermal Spray Conference, sponsored by DVS, ASM International, and IIW International Institute of Welding,
Basel, Switzerland, May 2–4, 2005, DVS-Verlag GmbH, Düsseldorf, Germany. 相似文献
2.
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
3.
Study on Process Optimization of Cold Gas Spraying 总被引:1,自引:0,他引:1
H. Tabbara S. Gu D. G. McCartney T. S. Price P. H. Shipway 《Journal of Thermal Spray Technology》2011,20(3):608-620
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.
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
6.
Aleem Anwaar Lianglinag Wei Hongbo Guo Baopeng Zhang 《Journal of Thermal Spray Technology》2017,26(3):292-301
Plasma spray–physical vapor deposition is a new process developed to produce coatings from the vapor phase. To achieve deposition from the vapor phase, the plasma–feedstock interaction inside the plasma torch, i.e., from the powder injection point to the nozzle exit, is critical. In this work, the plasma characteristics and the momentum and heat transfer between the plasma and powder feedstock at different torch input power levels were investigated theoretically to optimize the net plasma torch power, among other important factors such as the plasma gas composition, powder feed rate, and carrier gas. The plasma characteristics were calculated using the CEA2 code, and the plasma–feedstock interaction was studied inside the torch nozzle at low-pressure (20-25 kPa) conditions. A particle dynamics model was introduced to compute the particle velocity, coupled with Xi Chen’s drag model for nonevaporating particles. The results show that the energy transferred to the particles and the coating morphology are greatly influenced by the plasma gas characteristics and the particle dynamics inside the nozzle. The heat transfer between the plasma gas and feedstock material increased with the net torch power up to an optimum at 64 kW, at which a maximum of ~3.4% of the available plasma energy was absorbed by the feedstock powder. Experimental results using agglomerated 7-8 wt.% yttria-stabilized zirconia (YSZ) powder as feedstock material confirmed the theoretical predictions. 相似文献
7.
Analysis and optimization of the HVOF process by combined experimental and numerical approaches 总被引:1,自引:0,他引:1
Thermal spraying with the HVOF technology is a well known approach to dense metallic, ceramic and cermets coatings with good mechanical properties. Any attempt for improving HVOF coating properties requires a fundamental understanding of the mechanisms that occur during HVOF spraying. Thermal spray processes are not only optimized by empirical testing and by correlation analysis between process parameters and coating properties but also with numerical approaches. Recent attempts to understand the momentum and heat transfer mechanisms between flame and particles, and thus improve the control of the thermokinetic deposition process by analysis of fundamental thermophysical and fluid mechanical processes, have led to computational modeling of the spraying process and verification of simulation results by in-flight particle analysis.This paper focuses on modeling (tracking) of the particle properties during HVOF spraying using alumina powder. The particle properties are sensitive to a large number of process parameters (e.g., gas temperature, gas expansion velocity, pressure, spraying distance, spray powder particle diameter, nozzle geometry, etc.). Variation of the operating parameters of the HVOF process (gas flow rates, stoichiometric oxy/fuel ratio, nozzle design, etc.) is performed during modeling and simulation. The SprayWatch® system for particle in-flight measurement is used for verification of the numerical analysis result. 相似文献
8.
An analysis of the cold spray process and its coatings 总被引:9,自引:0,他引:9
In this study, computational fluid dynamics (CFD) and extensive spray tests were performed for detailed analyses of the cold
spray process. The modeling of the gas and particle flow field for different nozzle geometries and process parameters in correlation
with the results of the experiments reveal that adhesion only occurs when the powder particles exceed a critical impact velocity
that is specific to the spray material. For spherical copper powder with low oxygen content, the critical velocity was determined
to be about 570 m/s. With nitrogen as the process gas and particle grain sizes from 5–25 μm, deposition efficiencies of more
than 70% were achieved. The cold sprayed coatings show negligible porosity and oxygen contents comparable to the initial powder
feedstock. Therefore, properties such as the electrical conductivity at room temperature correspond to those of the bulk material.
The methods presented here can also be applied to develop strategies for cold spraying of other materials such as zinc, stainless
steel, or nickel-based super-alloys. 相似文献
9.
目的研究高压冷喷涂中,送粉气流在室温时主气流温度对冷喷涂粒子速度和温度的影响。方法利用计算流体力学软件FLUENT对冷喷涂流场进行数值模拟,分析不同送粉压差、不同喷管喉部直径的情况下,主气流温度对气体流场、粉末速度和温度的影响状况。结果送粉压差为0.1 MPa且喷管喉部直径为2 mm时,进入喷管的送粉气流流量占总气流流量的比值超过50%,此时提升主气流温度对冷喷涂粒子撞击速度和温度的提升幅度十分有限。在不改变送粉气流流量的情况下,增加喷管喉部直径可有效削弱送粉气流对粒子加速的不利影响。结论考虑送粉气流时,主气流温度对冷喷涂粉末沉积效果较弱,为了提高冷喷涂粉末沉积效率应保证顺利送粉的前提下尽可能地减小送粉气流流量,并且在设计喷管时应适当增加喷管喉部直径。 相似文献
10.
11.
Gas dynamic principles of cold spray 总被引:15,自引:0,他引:15
This paper presents an analytical model of the cold-spray process. By assuming a one-dimensional isentropic flow and constant
gas properties, analytical equations are solved to predict the spray particle velocities. The solutions demonstrate the interaction
between the numerous geometric and material properties. The analytical results allow determination of an optimal design for
a cold-spray nozzle. The spray particle velocity is determined to be a strong function of the gas properties, particle material
density, and size. It is also shown that the system performance is sensitive to the nozzle length, but not sensitive to the
nozzle shape. Thus, it is often possible to use one nozzle design for a variety of operational conditions. Many of the results
obtained in this article are also directly applicable to other thermal spray processes. 相似文献
12.
In cold gas dynamic spraying, the gas nature, process stagnation pressure and temperature, and the standoff distance are known to be important parameters that affect the deposition efficiency and coating quality. This investigation attempts to elucidate the effect of nozzle material on coatings produced using a downstream lateral injection cold spray system. Through experimentation, it is shown that the nozzle material has a substantial effect on deposition efficiency and particle velocity. It is proposed that the effects are related to complex interaction between the particles and the internal nozzle walls. The results obtained lead to the conclusion that during the particle/nozzle wall contact, a nozzle with higher thermal diffusivity transfers more heat to the particles. This heat transfer results in lower critical velocities and therefore higher deposition efficiencies, despite a noticeable reduction of particle velocities which is also attributed to particle-nozzle interactions. 相似文献
13.
R. Nickel K. Bobzin E. Lugscheider D. Parkot W. Varava H. Olivier X. Luo 《Journal of Thermal Spray Technology》2007,16(5-6):729-735
A new method for a combustion-free spraying is studied fundamentally by modeling and simulation in comparison with first experiments.
The article focuses on the numerical simulation of the gas-particle nozzle flow, which is generated by the shock reflection
at the end wall section of a shock tube. To study the physical fundamentals of this process, at present only a single shot
operation is considered. The particles are injected downstream of the nozzle throat into a supersonic nozzle flow. The measurements
of the particle velocity made by a laser Doppler anemometry (LDA) set up show that the maximum velocity amounts to 1220 m/s
for stainless steel particles of 15 μm diameter. The CFD-Code (Fluent) is first verified by a comparison with available numerical
and experimental data for gas and gas-particle flow fields in a long Laval-nozzle. The good agreement implied the great potential
of the new dynamic process concept for cold-gas coating applications. Then the flow fields in the short Laval nozzle designed
and realized by the Shock Wave Laboratory (SWL) are investigated. The gas flow for experimentally obtained stagnation conditions
is simulated. The gas-particle flow without and with the influence of the particles on the gas flow is calculated by the Surface
Engineering Institute (IOT) and compared with experiments. The influence of the injection parameters on the particle velocities
is investigated, as well.
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.
M. Doubenskaia D. Novichenko A. Sova D. Pervoushin 《Surface & coatings technology》2010,205(4):1092-1095
A diagnostic system based on non-intensified CCD image sensor is applied for particle-in-flight monitoring of different deposition processes: cold gas dynamic spray (CGDS), computer-controlled detonation spray (CCDS) and direct metal deposition (DMD). An additional illumination source for measuring particle velocity in CGDS and DMD processes is used. Particle velocity measurements are carried out aiming optimization of a Cold Spray nozzle with two zones of powder injection for spaying Al powder. In a pulsed-periodic process like detonation spraying, particle-in-flight visualization and velocity measurements are done by synchronizing detonation pulses with the CCD-camera-based diagnostic tool. A significant variation of particles velocity along the detonation plume is observed. In DMD process, dependence between the carrier gas flow rate and particle velocity is found. 相似文献
15.
An investigation is conducted of the gas dynamics of a gas detonation coating process and the mechanism of particle acceleration
by the shock wave inside the coating apparatus. Velocities of gas detonation in different gas mixtures are analyzed by applying
the conventional hydrodynamic theory of detonation, and the effect of addition gases on the velocity of detonation in oxygen/hydrogen
and oxygen/acetylene mixtures is studied. The authors propose a model that allows calculation of particle acceleration and
final velocity. This model utilizes the Chapman-Jouquet picture of detonation and assumptions about the linear distribution
of the velocity of detonation products behind the front of the detonation wave. The kinetics of particle acceleration by a
detonation wave exhibits several novel features and is distinctly different from particle acceleration in other methods of
spraying, such as plasma and high-velocity oxyfuel. There is a nonmonotonic dependence of particle velocity upon its coordinate
and change in the direction of particle acceleration. Loading distance and total barrel length are important parameters that
affect final particle velocity. Results indicate that final particle velocity and, as a consequence, the quality of detonation
coatings can be significantly affected by changing the gas mixture composition and the powder loading distance while keeping
the remaining operational parameters constant. 相似文献
16.
Production of titanium deposits by cold-gas dynamic spray: Numerical modeling and experimental characterization 总被引:2,自引:1,他引:2
T. Marrocco D. G. McCartney P. H. Shipway A. J. Sturgeon 《Journal of Thermal Spray Technology》2006,15(2):263-272
Over the past five years, interest in cold-gas dynamics spraying (CGDS) has increased substantially. Considerable effort has
been devoted to process development and optimization for such metals as copper and aluminium. This paper describes work undertaken
to expand the understanding of the deposition of titanium by cold-spray methods. CGDS deposits have been produced from commercially
pure titanium using room-temperature helium gas. The effect of different powder paticle size ranges, types of substrate, substrate
preparation methods, and spray parameter conditions on powder deposition have been investigated. Microhardness testing of
deposits was conducted, and their microstructures have been examined by scanning electron microscopy. Samples for pull-off
bond-strength tests have been prepared from a number of the more promising sets of spray parameters and adhesive strengths
determined. A one-dimensional numerical model of particle acceleration, employing isentropic gas flow behavior in the nozzle,
has also been used to estimate particle exit velocities. This model explicitly addresses the dependence of the drag coefficient
on gas compressibility and demonstrates its significance in terms of predicted particel velocities. By linking this model
with the measured particle size distributions, estimates of particle velocity distributions at the nozzle exit plane have
been computed. These allow an approximate value of the critical velocity for deposition of titanium to be made. Experimental
observations on the microstructure and properties of the deposits are discussed in light of powder particle size and velocity
distributions and the underlying physical and mechanical properties of the powders and substrates.
The original version of this paper was published in the CD ROM Thermal Spray Commects: Explore Its Surfacing Potential, International Thermal Spray Conference, sponsored by DVS, ASM International, and HW International Institute of Welding,
Basel, Switzerland, May 2–4, 2005, DVS-Verlag GmbH, Düsseldorf, Germany. 相似文献
17.
Cold spray nozzle mach number limitation 总被引:2,自引:0,他引:2
B. Jodoin 《Journal of Thermal Spray Technology》2002,11(4):496-507
The classic one-dimensional isentropic flow approach is used along with a two-dimensional axisymmetric numerical model to
show that the exit Mach number of a cold spray nozzle should be limited due to two factors. To show this, the two-dimensional
model is validated with experimental data. Although both models show that the stagnation temperature is an important limiting
factor, the one-dimensional approach fails to show how important the shock-particle interactions are at limiting the nozzle
Mach number. It is concluded that for an air nozzle spraying solid powder particles, the nozzle Mach number should be set
between 1.5 and 3 to limit the negative effects of the high stagnation temperature and of the shock-particle interactions. 相似文献
18.
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
19.
On Parameter Selection in Cold Spraying 总被引:2,自引:0,他引:2
H. Assadi T. Schmidt H. Richter J.-O. Kliemann K. Binder F. G?rtner T. Klassen H. Kreye 《Journal of Thermal Spray Technology》2011,20(6):1161-1176
For cold spraying, a method for the construction of the window of deposition and the selection of optimum process parameters is presented. Initially, particle impact velocity and the critical particle velocity for bonding are worked out and expressed explicitly in terms of key process and material parameters. Subsequently, the influence of particle velocity on coating characteristics is examined in view of the results of experiments and simulations. It has been found that main coating characteristics can be described as a unique function of the ratio of particle velocity to critical velocity, here referred to as ??. Finally, coating properties are linked directly to primary process parameters via parameter selection maps, where contours of constant ?? are plotted on a plane of gas temperature versus gas pressure. Inferences of the presented method and the resulting parameter selection maps are discussed for the example of copper as feedstock material. 相似文献
20.
Tantalum (Ta) coatings have been produced using a relatively new process, kinetic spray. Ta starting powders having particle
diameters greater than 65 μm are injected into a de Laval-type nozzle, entrained in a supersonic gas stream, and accelerated
to high velocities due to drag effects. The particles’ kinetic energy is transformed via plastic deformation into strain and
heat on impact with the substrate surface. Particles are not thermally softened or melted, producing relatively low oxide,
reduced residual stress, high adhesion and low porosity coatings. Analysis of the mechanical and physical properties of these
Ta coatings demonstrated increasing hardness, cohesive adhesion, and decreasing porosity as a function of particle velocity.
Comparison between kinetically sprayed coatings and coatings produced using conventional coating methods will be discussed. 相似文献