Effect of a cylindrical shroud on particle conditions in high velocity oxy-fuel spray process

Simulations of solid particles in a highly compressible gas flow in the high velocity oxy-fuel (HVOF) process are presented. The Eulerian formulation is used for the gas flow, and the particl phase is modeled by the Lagrangian method. Effects of attaching a cylindrical shroud to the end of the supersonic HVOF nozzle on gas and particle flows are analyzed. We found that the shroud significantly reduces the oxygen content in the field by protecting the supersonic jet from ambient air entrainment. The validation experiments were performed for the majority of process parameters such as shock formation, particle conditions, and coating oxygen content.     

微束等离子喷涂Al2O3陶瓷涂层特性

采用轴向中心送粉式微束等离子喷涂系统在2kW级的小功率条件下制备了Al2O3陶瓷涂层.研究了电弧功率、工作气体流量和喷涂距离对粒子速度与涂层组织结构和性能的影响.采用光学显微镜观察涂层的组织结构,采用X射线衍射分析涂层的相结构,采用磨粒磨损质量损失表征涂层的性能,用热辐射粒子速度温度测量系统测试工艺参数对喷涂粒子速度的影响.结果表明,电弧功率、工作气体流量和喷涂距离对粒子速度的影响都比较明显,粒子速度随着电弧功率和工作气体流量的增加而增加,随着喷涂距离的增加而下降.涂层的磨粒磨损质量损失随电弧功率的增加而减少,而随工作气体流量和喷涂距离的增加而增加.分析表明粒子的温度对涂层磨粒磨损质量损失有较大的影响.采用微束等离子喷涂可以制备磨粒磨损性能与传统等离子喷涂在38kW下制备的涂层相当的Al2O3涂层.     

Effect of heat treatment environment on the structural characteristics and microhardness of high velocity oxy-fuel sprayed tungsten carbide-cobalt coatings

In the present study, tungsten carbide-cobalt was coated on the austenitic stainless steel using high velocity oxy-fuel spraying. The as-deposited coatings were heat treated at 750 °C in air and argon gas environments. Structural characteristics of these coatings were studied using x-ray diffraction and Raman spectrum analysis. Further, the microhardness of the polished coated samples was also evaluated. The hardness of the coatings was significantly improved after heat treatment in air and argon gas environment. However, the highest hardness was observed with the coatings treated in argon gas environment. The formation of oxide phases such as tungsten trioxide and cobalt tungstate was observed after heat treatment in the air environment, whereas under the argon environment, no oxide phases were observed.     

固/液相等离子喷涂制备固体氧化物燃料电池复合电极

提出并研究以硅片为基体、采用固/液相等离子喷涂工艺制备固体氧化物燃料电池复合电极.固相送料方式喷涂阳极和阴极;悬浮液束流送料方式喷涂电解质.用CCD监测悬浮液束流与等离子射流形态,其特征分析结果表明最佳注射气压为0.25MPa.采用SEM和EDAX对电极涂层微观组织和组分进行分析,结果表明:喷涂距离是影响电解质涂层形貌...     

Development of dense corrosion resistant coatings by an improved HVOF spraying process

For 6 years, we have developed corrosion resistant coatings to protect steel structures in the marine environment by using a thermal spray technique. This paper summarizes the major developments and results obtained. Such a coating requires primarily impermeability and secondarily homogenous and clean microstructure. In order to make denser and highly corrosion resistant coatings, we selected spray materials and improved fabrication processes. HastelloyC was a suitable material for High Velocity Oxy-Fuel (HVOF) spraying to form corrosion resistant coatings because of its high resistance against thermal oxidation as well as seawater corrosion, especially crevice and pitting corrosion. An inert gas shroud system was attached with a commercial HVOF apparatus and this attachment increased the in-flight velocity of spray particles over 750 m s^?1 and simultaneously suppressed oxidation significantly. In addition, some new methods were designed to evaluate the sprayed particle’s state and the coating properties with high accuracy and sensitivity. Thermal energy of in-flight spray particles was revealed by molten fraction of spray particles, determined by quantitative analysis of melted and unmelted particles captured in an agar gel. Through-porosity of the coatings with open porosity below 0.1% was determined by using Inductively Coupled Plasma analysis of dissolved substance from substrate through the penetrating path of the coatings. The coating of HastelloyC nickel base alloy by the HVOF spraying with the gas shroud attachment had zero through-porosity and 0.2 mass% of oxygen content. The laboratory corrosion tests showed that the on-shroud HastelloyC coating was comparable to the bulk material of HastelloyC in terms of corrosion resistance. This coating, formed on steel, demonstrated an excellent protective performance over 10 months in the marine exposure test.     

Effects of spray parameters on the microstructure and property of Al2O3 coatings sprayed by a low power plasma torch with a novel hollow cathode

Al₂O₃ coating is deposited using a low power plasma torch with a novel hollow cathode through axial powder injection under a plasma power up to several kilowatts. The effects of the main processing parameters including plasma arc power, operating gas flow and spray distance on particle velocity during spraying, and the microstructure and property of the coating are investigated. The microstructure of the Al₂O₃ coating is examined using optical microscopy and X-ray diffraction analysis. The property of the coating is characterized by dry rubber wheel abrasive wear test. The velocity of in-flight particle is measured using a velocity/temperature measurement system for spray particle based on thermal radiation from the particle. The dependency of the microstructure and property of the coating on spray particle conditions are examined by comparing the particle velocity, and microstructure and abrasive wear weight loss of subsequent coating deposited by low power plasma spray with those of the coating by conventional plasma spray at a power one order higher. X-ray diffraction analysis of the coating revealed that Al₂O₃ particles during low power plasma spraying reach to sufficiently melting state prior to impact on the substrate with a velocity comparable to that in conventional plasma spraying. The experiment results have shown that processing parameters have significant influence on the particle conditions and performance of deposited Al₂O₃ coating. The coating of comparable microstructure and properties to that deposited by conventional plasma spray can be produced under a power one order lower. From the present study, it can be suggested that a comparable coating can be produced despite plasma power level if the comparable particle velocity and molten state are achieved.     

超音速等离子体喷涂MoSi2涂层工艺研究

涂层技术是C/C复合材料高温抗氧化与抗烧蚀的有效手段,单一的SiC涂层很难为C/C复合材料提供有效的长寿命保护。金属间化合物MoSi2高温时会形成一层致密的SiO2保护膜,具有特别优异的高温抗氧化性能,常作为C/C复合材料的高温抗氧化涂层。本文采用超音速等离子喷涂法在带SiC涂层的C/C复合材料表面制备了MoSi2涂层,主要研究了喷涂功率、主气(Ar)流量对粉料表面温度、飞行速度、沉积率以及对涂层表面微观结构和结合强度的影响。结果表明:喷涂功率在47.5~52.5 kW之间,既能使粒子有较高的速度和温度,还能保证粉末不过熔,在喷涂功率为50 kW时,粉料的沉积率最高,氧化不高,涂层表面致密性好,截面结合紧密,结合强度高;Ar流量为65 L/min时,能够保证MoSi2粉末有较高的表面温度与较快飞行速度,沉积率最高,氧化不高,涂层表面致密,几乎没有孔隙与裂纹。因此,调控超音速等离子体喷涂工艺参数能够在带SiC涂层的C/C复合材料表面得到致密且结合良好的MoSiO2涂层。     

聚变装置钨涂层面对等离子体材料的性能

对铜基体上真空等离子体喷涂1 mm的钨涂层进行了分析研究,主要包括微观结构、热力学属性以及成分分析.结果显示,钨涂层气孔率仅为7.6%,室温热导率达到79.7 W/(m·K),W/Cu结构界面结合强度高达45 MPa,这些结果对钨作为聚变装置面对等离子体材料的应用是令人鼓舞的.涂层材料的出气性能也是面对等离子材料的一个重要指标,钨涂层出气气体种类主要是氢气和水蒸气.而且在300℃经过4 h高温烘烤后出气率大幅度降低,更长时间的烘烤则对出气率影响不是太明显.因此可以看出钨涂层作为聚变装置面对等离子体材料的应用是可行的.     

Effect of Zr on microstructure of metallic glass coatings prepared by gas tunnel type plasma spraying

Metallic glass is one of the most attractive advanced materials, and many researchers have conducted various developmental research works. Metallic glass is expected to be used as a functional material because of its excellent physical and chemical functions such as high strength and high corrosion resistance. However, the application for small size parts has been carried out only in some industrial fields. In order to widen the industrial application fields, a composite material is preferred for the cost performance. In the coating processes of metallic glass with the conventional deposition techniques, there is a difficulty to form thick coatings due to their low deposition rate. Thermal spraying method is one of the potential candidates to produce metallic glass composites. Metallic glass coatings can be applied to the longer parts and therefore the application field can be widened. The gas tunnel plasma spraying is one of the most important technologies for high quality ceramic coating and synthesizing functional materials. As the gas tunnel type plasma jet is superior to the properties of other conventional type plasma jets, this plasma has great possibilities for various applications in thermal processing. In this study, the gas tunnel type plasma spraying was used to form the metallic glass coatings on the stainless-steel substrate. The microstructure and surface morphology of the metallic glass coatings were examined using Fe-based metallic glass powder and Zr-based metallic glass powder as coating material. For the mechanical properties the Vickers hardness was measured on the cross section of both the coatings and the difference between the powders was compared.     

铝基粉芯线材电弧喷涂工艺参数优化研究

为了使铝基粉芯线材电弧喷涂涂层获得优良的涂层性能,选择涂层孔隙率为判据,通过正交试验和OLYC IA m3金相图像分析系统对铝基粉芯线材电弧喷涂工艺进行了优化,同时采用SprayW atch热喷涂监控系统对喷涂过程中粒子的飞行速度和温度进行了测定.经研究得到了铝基粉芯丝材电弧喷涂的最佳工艺参数.结果表明,影响铝基涂层致密性的工艺因素按主次顺序分别为喷涂气压、喷涂电压和喷涂距离;在所选试验范围内,随气体压力和喷涂电压的增大、喷涂距离的减小,涂层的孔隙率降低;在优化的喷涂工艺参数条件下,铝基涂层最小孔隙率可达1.3%.     

APPLICATION OF HIPING-THICK CERAMIC COATINGS ONTO METALS

The demand for high performance in the combustion equipment used in the automobile and aerospace industries is creating renewed interest in the use of ceramic protective coatings on metal surfaces. Sometimes, thick coating layers are required as thermal barriers or for wear resistance and hardness. Although plasma spraying is one of the promising processes available for depositing thick ceramic coatings onto metal surfaces, the presence of porosity in the coating coupled with lack of corrosion resistance of the coated materials, and the generally low strengths of both the coating layer and the coating-matrix interface may limit the use of the process. HIP treatment of ceramic coatings allows one to obtain dense coatings and also to increase the interfacial bond strength. The present paper reviews the recent advances in the post-HIPing of ceramic coatings as well as the use of HIP for sinter-coating by which a ceramic powder compact is sintered and bonded simultaneously to a metal surface.     

Surface modification of implant materials and its effect on attachment and proliferation of bone cells

Osteoblast-like cell response in variation with the air plasma sprayed (APS) TiO2 coating process parameters correlated with coating properties were investigated to evaluate the durability and biocompatibility of the surface-modified implant. The Taguchi technique was used to determine the coating properties affected by plasma spraying parameters on Ti-6AI-4V alloy substrate. The coating properties were characterized by porosity and surface roughness using an image analyzer and surf analyzer, respectively. The MG-63 osteoblast like cell morphology and proliferation data on TiO2 coated substrate were measured by SEM observation and direct cell counting. It was demonstrated that surface roughness increased as spray distance decreased but gas flow rates and spray distance were major factors in the case of porosity. The osteoblast adhesion morphology and proliferation data indicated that osteoblast-like cell morphology was not influenced by process parameters, but cell proliferation was affected to some extent by surface roughness and porosity among TiO2 coated specimens. Specifically, the difference between those of substrate and coating layer was relatively more visible.     

铝合金上等离子喷涂金属镍层的研究

利用金相显微镜和扫描电镜对活塞铝合金表面等离子喷涂镍层(厚度为0. 1～ 0. 2mm ) 的金相组织、形貌和界面进行了观察。发现在铝合金与带状喷涂镍层之间存在较厚氧化膜形成的不规则熔合线, 阻碍焊合效果。因此在现有工艺条件下, 镍层与铝合金间难以实现冶金熔合效果, 并对它们之间的连接机理进行了探讨。      

Nanostructured tungsten oxide with controlled properties: Synthesis and Raman characterization

Tungsten oxide thin films are interesting for their electrochromic and gas sensing properties. For technological applications, the control of morphology (effective surface, porosity) and structure (crystallinity, stoichiometry) at the nanoscale is of paramount interest to deliver distinctive properties.Nanostructured tungsten and tungsten oxide films have been synthesized by nanosecond pulsed laser deposition (PLD) starting from a W metallic target. Both inert and reactive buffer gases (He, Ar, dry air) have been exploited to induce cluster formation and/or oxidation and to vary the deposition energies of ablated species. A wide range of morphologies extending from compact and smooth, up to extremely porous and spongy-like structures have been obtained.The structure, the oxide phase and the degree of crystallinity of the films have been investigated by Raman spectroscopy. Films deposited in the presence of inert buffer gases reveal a spontaneous ex-situ oxidation, when exposed to ambient atmosphere, which is strongly related to the nanostructure. Instead, deposition in a varying pressure of dry air permits to grow tungsten oxide films and to tune their structure from amorphous to nano- and microcrystalline with different coexisting oxide phases.     

不同喷涂工艺下NiCoCrAlYTa涂层的显微结构和性能

为探索不同喷涂工艺对NiCoCrAlYTa涂层的显微结构和性能的影响规律,确定最优工艺,采用大气等离子、低压等离子、常规超音速火焰和低温超音速火焰4种工艺在镍基单晶高温合金表面制备了NiCoCrAlYTa涂层。采用X射线衍射(XRD)、扫描电镜(SEM)和显微硬度计等分析手段对喷涂态涂层的相组成、显微结构和显微硬度等进行了表征。结果表明,不同喷涂工艺下涂层的相组成均为γ′-Ni_3Al、β-NiAl和γ-Ni固溶体。低压等离子和超音速火焰喷涂的涂层致密且孔隙率低,其中超音速火焰喷涂的涂层孔隙率低于1%。低压等离子和低温超音速火焰喷涂的涂层氧含量很低,控制在0.3%~0.6%的范围。综合来说,低温超音速火焰喷涂工艺制备的涂层结构致密,孔隙率和氧含量很低。该工艺是沉积NiCoCrAlYTa涂层的首选。     

Nanostructured Sulfide Composite Coating Prepared by Atmospheric Plasma Spraying

Nanostructured FeS-SiC coating was deposited by atmospheric plasma spraying (APS). The microstructure and phase composition of the coating were characterized with SEM and XRD, respectively. In addition, the size distribution of the reconstituted powders and the porosity of the coating have been measured. It was found that the reconstitiuted powers with sizes in the range of 20 to 80 μm had excellent flowability and were suitable for plasma spraying process. The assprayed FeS-SiC composite coating exhibited a bimodal distribution with small grains (30～80nm) and large grains (100～200nm). The coating was mainly composed of FeS and SiC, a small quantity of Fe1-x S and oxide were also found. The porosity of the coating was approximately 19 %.     

正交试验设计优化等离子喷涂纳米Al2O3-13%TiO2涂层工艺参数

为了深入研究等离子喷涂纳米Al2O3-13%TiO2(质量分数)工艺参数与涂层性能之间的关系,采用正交试验设计法,针对等离子喷涂过程中喷涂距离、喷涂电流、主气压力及辅气压力等4个主要参数,选用L9(34)正交表,以涂层结合强度为指标开展制备工艺参数的优化。结果表明,影响涂层结合强度的因素主次顺序是喷涂电流、喷涂距离、主气压力、辅气压力;等离子喷涂纳米Al2O3-13%TiO2最佳工艺参数为:喷涂距离110mm,喷涂电流870A,主气压力0.31MPa,辅气压力0.97MPa,优化工艺喷涂的涂层结合强度达到31.5MPa。     

Cr3C2-NiCr涂层对水力机械材料耐磨蚀性能影响研究

以水力机械材料中的A3钢为基体材料,选取UDS-200全自动爆炸喷涂系统为喷涂设备,通过不同喷涂功率在A3钢表面喷涂了5种不同孔隙率的Cr₃C₂-NiCr涂层样品。采用FE-SEM和显微硬度计,研究了Cr₃C₂-NiCr涂层样品的表面形貌和显微硬度;通过摩擦磨损试验和中性盐雾腐蚀试验,研究了Cr₃C₂-NiCr涂层样品对水力机械材料的耐磨性能和耐腐蚀性能的影响。结果表明,实施摩擦磨损后,Cr₃C₂-NiCr涂层样品表面的磨痕部位比其余部位更为光滑,磨痕呈现清晰的条纹状;Cr₃C₂-NiCr涂层样品的摩擦系数呈现先升高后降低的趋势,升高和降低的波动幅度较小,摩擦系数基本稳定在0.6左右;Cr₃C₂-NiCr涂层属于脆性材料,其质量磨损率与摩擦角度和摩擦速度成正比,而与摩擦温度成反比,孔隙率越高耐磨性能越差;Cr₃C₂-NiCr涂层样品的孔隙率越高,耐腐蚀性能就越差;随着孔隙率的逐渐提升,Cr₃C₂-NiCr涂层样品的失重量和失重速率均不断提升;喷涂层数越多,则Cr₃C₂-NiCr涂层的腐蚀速率越低,耐腐蚀性能越好,能够更好地保护水力机械材料不被介质腐蚀。     

Development of simplified active flux tungsten inert gas welding for deep penetration

A new advanced active flux tungsten inert gas (AA-TIG) welding technique, named cap active flux tungsten inert gas (CA-TIG) welding using atmospheric oxygen, was proposed to increase the penetration depth of a weld. Only a simple nozzle cap with an air inlet was used for the welding. Flowing inert gas used as a shielding gas through a nozzle center led to the aspiration of oxygen from the atmosphere to the molten pool. The penetration depth was increased by the reversal of the Marangoni convection due to the entrained oxygen, and it reached three times deeper than that of the conventional TIG welding. Additionally, no degradation of the tungsten electrode was observed because it was protected by the inert gas. The penetration depth was changed by the oxygen content in the molten pool and it could be easily controlled by the nozzle cap design and the welding parameters.