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1.
Agglomerated titania nanopowder and a “classical” titania were sprayed by the high throughput water-stabilized plasma (WSP)
and thoroughly compared. Optical microscopy with image analysis as well as mercury intrusion porosimetry were used for quantification
of porosity. Results indicate that the “nano” coatings in general exhibit finer pores than coatings of the “conventional”
micron-sized powders. Mechanical properties such as Vickers microhardness and slurry abrasion response were measured and linked
to the structural investigation. Impact of the variation in the slurry composition on wear resistance of tested coatings and
on character of the wear damage is discussed. The overall results, however, suggest that the “nano” coatings properties are
better only for carefully selected sets of spraying parameters, which seem to have a very important impact.
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
2.
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
3.
The velocity, temperature, entrained air fraction, and Ar/He concentration profiles were measured in a subsonic thermal plasma
jet using an enthalpy probe and mass spectrometer. Through interaction with the surrounding atmosphere, air is quickly entrained
into the jet, resulting in rapidly decreasing velocities and temperatures. Due to the difference in ionization potential,
a significant diffusive separation or demixing of Ar and He is also observed in the large temperature gradients present. Near
the exit of the torch, in the jet center, the relative He concentration is enhanced by approximately 50% over that of the
premixed feed gases. Demixing occurs primarily in the discharge region and torch nozzle. As jet mixing progresses in the downstream
direction, the Ar to He ratio approaches the initial input ratio. 相似文献
4.
Recently, direct current (dc) plasma torches equipped with converging-diverging (Laval) nozzles, instead of standard cylindrical
ones, have been shown to present several advantages for both vacuum and atmospheric plasma spraying, such as diminishing the
gradients of temperature and velocity and reducing the turbulence intensity in the jet fringes. The present study was concerned
with the diagnostics of the plasma jets produced by three nozzles of various contours: a standard cylindrical anode and a
Mach 2.5 and Mach 3 Laval nozzle. Emission spectroscopy (absolute intensity) and enthalpy probe techniques were used to measure
temperature and velocity fields. Special attention was given to the effects of spray chamber pressure on flow regime inside
the nozzles and to the distribution of the temperature and velocity fields in the plasma jet. Results showed that under the
chamber pressure conditions used (vacuum), for which Laval nozzles originally were designed, the generated plasma jets had
greater centerline velocities and larger high temperature zones compared to standard cylindrical nozzles. The results showed
significant improvement in the deposition efficiency by using nozzles with these computed contours. 相似文献
5.
采用CCD图像采集系统与图像处理技术提取等离子射流长度;以红外测温仪检测的单位时间内基体温度变化来衡量加热效应,研究不同熔射距离与射流长度条件下射流和粉末粒子流对基体的加热效应特点.结果表明,当熔射距离不大于射流长度时,基体温升主要来至于射流加热效应;随着熔射距离增大,射流对基体的加热效应迅速减弱;当熔射距离大于射流长度时,粒子流加热效应比较明显.提出射流长度可以作为合理选择熔射距离的特征评价指标,并通过不同熔射距离条件下熔射皮膜的截面尺寸以及形貌进行验证. 相似文献
6.
Diagnostics of thermal spraying plasma jets 总被引:1,自引:0,他引:1
P. Fauchais J. F. Coudert M. Vardelle A. Vardelle A. Denoirjean 《Journal of Thermal Spray Technology》1992,1(2):117-128
7.
V.A. Frolov V.A. Poklad B.V. Ryabenko D.L. Kozlov A.V. Zimareva 《Welding International》2013,27(3):244-247
Coat obtaining techniques using industrial plasma spraying systems of transformed powder material feed system into plasma jet are considered. 相似文献
8.
Yang Gao Lian-Tong An Cheng-Qi Sun Zhi-Jun Yan 《Journal of Thermal Spray Technology》2004,13(4):521-525
The effects of the composition of plasma gases (Ar-N2, Ar-H2), arc current, and voltage on the temperature and velocity of a low-power (5 kW) plasma torch in the arc field free region
has been investigated using an enthalpy probe. Coatings of Al2O3-13TiO2 were deposited under different conditions. The results show that in the Ar-N2 plasma, the enthalpy, temperature, and velocity change little with arc current and voltage when regulating the nitrogen proportion
in the plasma gas. The hardness of the resulting coatings is 800 to 900 kg/mm2 HV.300. For Ar-H2 plasma, however, increases in the H2 content in the mixture of the gases remarkably enhanced the velocity and heat transfer ability of the plasma jet, with the
result that the coatings showed high hardness up to 1200 HV. 相似文献
9.
A new design is proposed for direct current plasma spray gas-shroud attachments. It has curvilinearly shaped internal walls
aimed toward elimination of the cold air entrainment, recorded for commercially available conical designs of the shrouded
nozzle. The curvilinear nozzle design was tested; it proved to be capable of withstanding high plasma temperatures and enabled
satisfactory particle injection. Parallel measurements with an enthalpy probe were performed on the jet emerging from two
different nozzles. Also, corresponding calculations were made to predict the plasma flow parameters and the particle parameters.
Adequate spray tests were performed by spraying iron-aluminum and MCrAlY coatings onto stainless steel substrates. Coating
analyses were performed, and coating qualities, such as microstructure, open porosity, and adhesion strength, were determined.
The results indicate that the coatings sprayed with a curvilinear nozzle exhibited lower porosity, higher adhesion strength,
and an enhanced microstructure. 相似文献
10.
The flow of gas mixtures in a dc plasma torch is studied using the CFD PHOENICS (CFD PHOENICS, Berkeley, CA) code. In the model, the cold gas mixture (300 K), initially constituted of 85 vol% Ar and 15 vol% H, is introduced into a power input zone where it takes energy and is ejected in the surrounding atmosphere at constant pressure (105 Pa). The flow is assumed to be in chemical equilibrium. Equations of mass, momentum, and energy are discretized using a control-volume method. The turbulent flow is modeled by a k-ɛ two-equations model for the turbulent kinetic energy and its dissipation rate. Finally, the algebraic coupling equations set is solved by means of the SIMPLEST algorithm, implemented into the CFD code, using a hybrid interpolation scheme. Results concern the effect of the torch power on the ArH2 flow. The phenomenon is analyzed through the evolution of velocity and temperature inside and outside the torch. From these calculations, the effect of ambient gas entrainment by the jet is emphasized and a comparison of the level of entrained gas is made with experimental data. 相似文献
11.
低压等离子喷涂由于具有特殊的射流特性,以及可以沉积组织均匀的特殊结构涂层而备受关注.涂层的形成受到等离子射流特性的影响,比如焓值、温度、速度等.研究中利用热焓探针技术在环境压力为3 kPa的条件下,测量了Ar-H2等离子体不同轴向位置射流中心的焓值和压力,并且进一步计算了射流的温度和速度,以及表征等离子体对粉体加热能力的努森数.结果表明,等离子射流在距离喷嘴出口12.5 mm处的温度为11 000 K;400 mm处降为7 000 K;等离子射流速度在喷嘴出口处25 mm左右达到最大值,约为2 000 m/s;喷嘴外部等离子射流的努森数处于过渡区,对粉体的加热能力较低. 相似文献
12.
Using statistical design of experiments, the arc current, total gas flow rate, percent secondary gas (He), and powder feed
rate have been varied to assess the torch behavior and establish its correlation to coating properties. The torch response
includes arc voltage drop, torch efficiency, and plasma jet geometry. High-speed images of the luminous plasma jet for each
operating condition have been acquired with a LaserStrobeℳ videocamera, and image analysis has been used to quantify the jet
length and jet fluctuations as additional torch responses. Porosity and unmelted particles, which are determined using image
analysis of a micrograph of a NiAl coating cross section, were selected as principal coating characteristics. These findings
are expected to be useful for optimization of new spray processes and for evaluation of new torch designs. 相似文献
13.
建立一个三维的统一的双钨极TIG焊模型,利用磁流体动力学理论对双钨极、电弧、阳极三个区域进行统一求解,获到双钨极电弧的压强分布,探究等离子体喷射与对电弧压强的关系。研究发现,双钨极TIG在钨极下方、阳极上方以及两束等离子体流交汇处存在较大的电弧压强,这些高压区的形成与等离子体喷射存在因果关系。计算发现,双钨极TIG焊在阳极表面上的最大压强远小于单钨极TIG焊的,这为双钨极TIG焊的应用提供了一些理论基础。 相似文献
14.
The material of Zerodur is widely used in high performance optics because of its excellent thermal stability characteristics. This paper deals with the development of an APPJ (Atmospheric Pressure Plasma Jet) chemical machining process for defect free and high efficiency machining of Zerodur. The APPJ chemical machining mechanism for multi-phase multi-composite materials is presented. The chemical property of the plasma jet is investigated via the atom emission spectrum analysis method and the experimental results of Zerodur material removal function and surface roughness variation with different processing parameters are discussed. Scientific explanations for the experimental observations are given. 相似文献
15.
结合图像处理与模式识别技术提取等离子射流的形态特征,采用射流狭长度对其进行表征.采用数据挖掘技术将等离子弧电流、电压参数和射流狭长度特征进行聚类分析,构造对等离子熔射过程中射流发生子系统进行智能化控制的知识库.根据涂层的残余应力、孔隙率和硬度等主要性能参数以及微观组织结构对分类结果进行质量评判,生成工艺参数到最佳分类的推理规则集,从而实现了对工艺参数—射流形态—涂层性能之间关联关系的研究.基于规则库监督多模型自适应控制系统结构,提出了一种等离子射流发生子系统的智能化控制策略. 相似文献
16.
17.
目的 为了研究等离子射流特性,方法 本文借助响应曲面法,以粒子速度和温度作为指标来反映射流特性的变化,采用Box-Behnken-Design ( 简称BBD)设计分析了电流、主气以及次级气比例这三个影响因素对于射流特性的影响规律以及参数之间的相互作用关系。结果 研究表明:对于粒子速度的影响因素排序中:QAr > I > C, 对于粒子温度的影响因素排序中:I > QAr > C。该喷嘴下实现最佳加热效应的参数配比为:主气大小80L/min、电流450A,次级气比例为17.5%;实现射流最佳加速效应的离子气及电参数配比方案为:主气大小120L/min、电流450A,次级气比例为12.5%;在射流最佳加速效应对应参数下制备AT40涂层进行验证,发现涂层均匀致密,孔隙少。结论:运用响应曲面法分析和解决等离子射流特性影响问题具有科学性和可操作性,借助射流特性的研究能够有效指导涂层制备。 相似文献
18.
Stéphane Vincent Guillaume Balmigere Erick Meillot 《Surface & coatings technology》2009,203(15):2162-2171
A numerical simulation of the interaction between a plasma flow and a liquid jet was investigated, leading to the proposal of a compressible model, based on augmented Lagrangian, Large Eddy Simulation (LES) turbulence modeling and Volume of Fluid (VOF) approaches, capable of managing incompressible two-phase flows as well as turbulent compressible motions. The VOF method utilized volume markers to advect the local concentration of gas and liquid in a Eulerian manner. The numerical model was validated on single-phase plasma configurations as well as two-phase cross flow liquid jet interactions. Finally, an example of the first simulations of the interactions between a liquid jet and a plasma is presented. However improvements should be realized as to increase the speed of the VOF-SM algorithm or add specific subgrid models related to jet fragmentation and phase change. 相似文献
19.
Pure iron samples were exposed to thermal plasma jet and nitrided for 15 min at a temperature ranging from 545 °C to 742 °C. For comparison purposes, conventional ion nitriding was also performed using glow discharge plasma at 580 °C for 8 h. For conventional plasma nitriding, a top compound layer and a bottom diffusion zone are observed. In contrast, an additional “transition zone” is observed between the compound layer and the diffusion zone for the thermal plasma jet treatment when the process temperature is 667 °C or above. This “transition zone” is quite thick (a few tens of micrometers), determined by the treatment temperature, and has unique features in the phase formation and nitrogen distribution. At 706 °C, the content of γ′phase, as well as the content of nitrogen and the hardness, reaches the maximum. Compared with the traditional plasma nitriding process, the reaction speed of thermal plasma irradiation is much higher. A nitrided case depth over a few tens of micrometers is obtained in plasma jet nitriding for only 15 min versus a depth of only a few micrometers in conventional plasma nitriding for 8 h. The formation of the “transition zone” and the mechanism for the high nitriding speed are discussed in the paper. It is believed that this technology can be applied at atmospheric pressure in field without the requirement for a vacuum system. Hence, this technology may be advantageous for practical applications. 相似文献
20.
Two types of plasma torch for cutting of metals, working with narrow-jet (exact or constricted) plasma, are described. Methods of modernizing the plasma torches proposed taking into account the principles and design methods developed by the authors are outlined. The efficiency of design is analysed using acoustic safety criteria. The results of comparative analysis of the noise characteristics of Russian and foreign plasma torches for cutting in sound and ultrasonic noise emission ranges are presented. The advantages of the new narrow-jet plasma torch determined on the basis of the acoustic safety criterion in comparison with both the basic model and other investigated plasma torches are discussed. 相似文献