喷涂距离对Fe基非晶涂层孔隙影响的研究

热喷涂涂层中孔隙的存在会降低涂层的耐蚀性,减少涂层寿命,而热喷涂工艺参数很大程度上影响涂层的孔隙率。本文采用计算机数值模拟和设计验证实验的分析方法,重点研究了JP-8000超音速火焰喷涂系统(HVOF)制备Fe基非晶涂层工艺参数中喷涂距离与涂层孔隙的关联性。利用商用计算软件Fluent计算平台,研究加入粉末粒子前,喷枪内火焰温度和速度的变化规律,以及加入非晶粉末后,不同喷涂距离条件下颗粒飞行过程的温度和速度的变化规律。仿真结果表明,喷涂距离为360~380 mm时,非晶粉末颗粒在撞击基板时处于半融化状态,颗粒在基板上具有良好的流动性,可获得孔隙率较低的涂层。验证实验结果与仿真结果一致。X射线衍射结果表明,粉末、不同喷涂距离所制备的涂层以及同成分的非晶条带均为完全非晶态结构。SEM和孔隙率统计结果表明,喷涂距离为370 mm时,涂层截面的孔隙较少,且孔隙率最低,为0.57%,验证了计算模拟优化的最佳喷涂距离范围。     

Aluminium and silicon base coatings for high temperature alloys—Process development and comparison of properties

The paper is concerned with systematic studies on the formation of overlay coatings on nickel and iron base superalloys to improve their resistance against high temperature oxidation and hot corrosion. In contrast to the simpler case of aluminizing nickel base alloys, the problems arising in aluminizing iron base superalloys and in siliconizing nickel base alloys have not yet been solved.A new and economical coating procedure is presented, which involves a reaction sintering process of unalloyed powder mixtures to obtain overlay coatings. The influence of the compositions of the layer and the substrate on the chemical compatibility of the whole layer composite is described in detail. It is shown that overlay coatings containing high concentrations of silicon can only be applied on nickel base superalloys if elements that are able spontaneously to form reaction barriers are present within the substrate alloy (e.g. aluminium) or in the as-preformed interlayer. Refractory metals have proved to be the most advantageous.To obtain a ductile coating, silicon-rich donor phases in the form of isolated precipitates were incorporated into a matrix containing low concentrations of silicon. These coating systems can also be applied to improve the aluminization of iron base alloys. The high temperature oxidation and corrosion behaviours of the coated samples were tested in burner gas or air at 1000°C and in molten salts at 900°C.     

Warm spraying—a novel coating process based on high-velocity impact of solid particles

Abstract

In recent years, coating processes based on the impact of high-velocity solid particles such as cold spraying and aerosol deposition have been developed and attracting much industrial attention. A novel coating process called ‘warm spraying’ has been developed, in which coatings are formed by the high-velocity impact of solid powder particles heated to appropriate temperatures below the melting point of the powder material. The advantages of such process are as follows: (1) the critical velocity needed to form a coating can be significantly lowered by heating, (2) the degradation of feedstock powder such as oxidation can be significantly controlled compared with conventional thermal spraying where powder is molten, and (3) various coating structures can be realized from porous to dense ones by controlling the temperature and velocity of the particles. The principles and characteristics of this new process are discussed in light of other existing spray processes such as high-velocity oxy-fuel spraying and cold spraying. The gas dynamics of particle heating and acceleration by the spraying apparatus as well as the high-velocity impact phenomena of powder particles are discussed in detail. Several examples of depositing heat sensitive materials such as titanium, metallic glass, WC–Co cermet and polymers are described with potential industrial applications.     

Characterization and comparison between APS coatings prepared from ball milled and plasma processed nickel–aluminium powders

Plasma spraying has wide range of applications which include corrosion, thermal and abrasion resistance coatings. In the present work, nickel and aluminium powders were ball milled and the same were thermal plasma processed to produce spherical nickel alumindes particles. Both ball milled and plasma processed powders were spray deposited on stainless steel (SS 304) substrate using atmospheric plasma spray technique (APS). The experiments were carried out for different plasma input power levels, torch to base distances and coating thicknesses. Microstructure, micro hardness, adhesive strength, and porosity of the coatings are reported and discussed. Effect of plasma processing parameters and plasma spheroidization of powders on coating properties has been evaluated and reported. High plasma power, low torch to base distance lead to high temperature supplied to in-flight particles which correspond to high hardness, low porosity and high adhesion. Spherical morphology and formation of nickel aluminide intermetallic were achieved by plasma spheroidization. Coatings prepared from plasma processed powders enhance the coating properties positively.     

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.     

Numerical simulation of coating growth and pore formation in rapid plasma spray tooling

Rapid plasma spray tooling (RPST) is a process that can quickly make molds from rapid prototyping or nature patterns without limitation of pattern's size or material. In this paper, the process of coating growth and pore formation in RPST has been analyzed by numerical simulation. The objective of this work was to determine the porosity in plasma sprayed coatings and verify the developed computer model, which might serve for future thermal residual stress studies of plasma sprayed coatings. The analysis was divided into two steps: particle flattening and coating growth. In the analysis, a ballistic model was used for modeling the in-flight powder particles. The method allows for the calculation of off-normal spray angle, which is common in plasma spraying of engineering components. Also, a set of rules for coating growth as well as pore formation in the coating has been proposed. Based on these works, a computer program was developed to calculate the effects of process parameters, such as gun scanning velocity, spray angle, etc., on the porosity of the coating. Finally, an experiment was carried out to verify the effects of spray parameters on the porosity. The results agree with the prediction of the model.     

Influence of the HVOF spraying process on the microstructure and corrosion behaviour of Ni-20%Cr coatings

The microstructure and the aqueous corrosion resistance of coatings produced by High Velocity Oxy-Fuel (HVOF) spraying techniques has been investigated. Two types of spraying processes have been employed i.e., Topgun HVOF using propylene gas and Met-Jet II HVOF with kerosene liquid fuel together with two forms of Ni-20%Cr powders i.e., water and inert gas atomised. The oxide, porosity and the amount of melted material in the coatings were characterised using scanning electron microscopy (SEM) and X-ray diffraction (XRD), whilst the corrosion resistance of the coatings and the ability to protect the underlying mild steel substrate was evaluated by use of a salt spray chamber and potentiodynamic tests.MetJet II produced coatings from gas-atomised powder with a lower oxide content, a reduction in porosity and less melted material, as the residence time of particles in the combusted gas stream was shortened. Water atomised powder formed a higher volume fractions of unmelted material and porosity when compared with gas-atomised powder coatings. This was encouraged by the presence of a thin oxide layer, which formed during the production of the water-atomised powder. The orientation of oxides and pores in the coatings had a major effect on their aqueous corrosion behaviour. Better protection for the underlying steel substrate (>3000 h exposure in a salt spray test) was obtained with the coating produced from the gas-atomised powder with the MetJet II system, which had the lowest porosity/oxide content running perpendicular to the substrate surface. The major factor in preventing attack on the mild steel substrate is the amount of interconnecting porosity which allows the corrodant to percolate through the coating.     

等离子沉积氧化锆涂层显微组织及性能研究

目的以氧化锆粉末作为喷涂材料,使用等离子喷涂的方式制备出性能优异的氧化锆涂层。方法通过不同的工艺参数来对涂层的显微组织及性能进行优化,分别利用扫描电镜(SEM)、X射线衍射分析仪(XRD)等方法,研究了工艺参数对涂层显微组织影响,并通过高温氧化测试来研究涂层的抗高温性能。结果在其他喷涂条件固定的情况下,涂层的厚度与喷涂时送粉量有关,送粉量越高则涂层厚度越大;当改变喷涂距离时,涂层的致密度则随着喷涂距离的增加而降低;在高温氧化40h后,涂层表面没有发生明显变化。结论通过等离子喷涂制备的氧化锆涂层具有较好的致密度,孔隙率最低仅为3.24%;涂层具有良好的热稳定性,能够长时间在高温下稳定使用。     

Synthesis and Deposition of TiC-Fe Coatings by Oxygen-acetylene Flame Spraying

A simpler and more convenient method for producing wear-resistant, TiC-reinforced coatings were investigated in this study. It consists of the simultaneous synthesis and deposition of TiC-Fe materials by oxyacetylene flame spraying. Solid reagents bound together to form a single particle are injected into the flame stream where an in-situ reaction occurs. The reaction products are propelled onto a substrate to form a coating. Microstructural analyses reveal that TiC and Fe are the dominant phases in the coatings. The reaction between Ti and C happens step by step along with the reactive spray powder flight, and TiC-Fe materials were mainly synthesized where the spray distanceis 125～170 mm. The TiC-Fe coatings are composed of alternate TiC-rich and TiC-poor lamellae with different microhardness of 11.9～13.7 and 3.0～6.0 GPa, respectively. Submicron and round TiC particles are dispersed within a ductile metal matrix. The peculiar microstructure is thought to be responsible for its good wear resistance, which is better nearly five times than WC-reinforced cermet coatings obtained by traditional oxyacetylene flame spray.     

基于替代电镀硬铬的WC增强金属复合涂层疲劳性能的研究现状

传统电镀硬铬涂层存在网纹裂纹缺陷、抗疲劳性能不足以及环境污染严重等问题,针对新一代航空工业急需新技术替代传统电镀硬铬这一迫切需求,研发新型的耐磨耐蚀涂层体系及其先进环保的再制造技术迫在眉睫。根据先进涂层技术的发展情况,研发出了基于高温熔化-凝固技术的物理气相沉积、超音速火焰喷涂以及激光熔覆技术,这在绿色制备航空工业用耐磨耐蚀涂层上表现出了一定的应用前景,并表现出了比传统电镀硬铬更长的疲劳寿命,但其仍存在内应力过高而开裂、粉末氧化或相变导致疲劳性能下降等一系列关键问题。近年来,冷喷涂涂层技术作为先进环保的新技术,凭借其低温固态沉积特性在制备金属基复合涂层上展现出了显著的冶金优势,其中冷喷涂涂层的残余压应力有助于提高零件的疲劳性能。此外,从起落架防护涂层沉积到其修复再制造环节,冷喷涂技术均可参与其中。因此,作为固态沉积工艺的冷喷涂,其在替代传统电镀铬的新型涂层制备工艺方面具有显著的应用潜力,未来的研究将集中于优化冷喷涂涂层材料和工艺上,以进一步提高其力学性能和疲劳性能。     

Plasma spray synthesis of TiB2-Fe coatings

A limiting feature of the plasma spray process is the need for the powder to melt during its passage through the plasma flame. It is quite impossible to obtain coatings with materials that are difficult to melt. However, metal borides, particularly titanium boride, are attractive. Because of their high melting point, satisfactory coatings based on these materials have not been achieved.To overcome this problem, a process for making TiB₂-Fe coatings was studied. The TiB₂-based coatings were produced by the reaction of ferrotitanium with boron. The TiB₂ formation was first studied by thermal differential analysis and X-ray diffraction. It was observed that TiB₂ is formed at low temperature by an exothermic reaction. The characteristics of the reaction products obtained at different reaction temperatures are described.Agglomeration techniques were used to prepare the reagents: fine powders of ferrotitanium alloy and boron. TiB₂-Fe coatings were produced by plasma spraying the agglomerated powders. The influence of the plasma spray process parameters and the powder preparation techniques on the coating microstructure is discussed.Thick hard coatings comprising compounds of the reagent materials are produced during spraying by this synergetic process. Such coatings may be suitable for wear resistance applications.     

喷涂工艺对Fe-Ni-B喷涂涂层组织性能的影响

采用高速火焰喷涂技术以及等离子喷涂技术制备了Fe-Ni-B涂层.利用扫描电子显微镜(SEM)、X射线荧光光谱仪(EDX)分析了粉末以及涂层的微观结构、涂层到基体的成分分布.利用X射线衍射(XRD)分析了喷涂态的涂层物相.并对涂层的结合强度及抗热震性能进行了试验研究.研究结果认为:等离子喷涂层组织更为致密,但其热喷涂涂层存在的层状结构也更加明显.熔融液滴在涂层表面的平铺效果都比较好.Fe、Ni元素的分布从涂层到基体基本成均匀分布,避免了局部元素偏析所造成的应力集中.热震后,等离子喷涂涂层中的裂纹分布细小且无规律.高速火焰喷涂涂层裂纹主要集中在涂层与基体结合部位.根据材料抗热震性能的能量理论和弹性理论,等离子喷涂涂层的抗热震能力更强.并且涂层的断裂失效主要产生在结合部位.     

Mercury porosimetry analysis of magnetic coatings

Mercury porosimetry can be used to characterize the structure of magnetic tape coatings but to get accurate information, compressibility corrections for the sample cell and basefilm must be made. Equations to make these corrections have been developed and published previously. These equations have been used to help interpret recent studies of tape coatings. These analyses have shown: 1. The Critical Pigment Volume Concentration (CPVC) of a magnetic pigment can be determined by measuring the mercury porosity of actual magnetic tapes. This CPVC can differ from the CPVC determined from tensile measurements of thick uncalendered coatings. 2. Postcuring of magnetic metal powder coatings was followed by measuring porosity and compressibility with mercury intrusion. The curing with isocyanate follows a first order reaction kinetics and is a relatively slow process, even after 7 days of storage the coating is not fully cured. 3. Multipass durability of (metal powder) audio tapes is directly correlated with porosity of the coating layer. For durable tapes porosity must be absent.     

Coatings for fast breeder reactor components

Several types of metallurgical coatings are used in the unique environments of the fast breeder reactor. Most of the coatings have been developed for tribological applications, but some also serve as corrosion barriers, diffusion barriers or radionuclide traps.The tribological coatings must meet a variety of performance criteria for friction coefficients, wear rates, galling resistance and self-welding resistance in liquid sodium. In addition, most applications require the coating to exhibit long-term resistance to sodium corrosion, resistance to damage by thermal cycling at temperatures up to 625°C and, for core applications, resistance to irradiation damage to neutron fluences of 6 × 10²² neutrons cm^-2 or more.The materials that have consistently given the best performance as tribological coatings in the breeder reactor environments have been coatings based on chromium carbide, nickel aluminide or Tribaloy 700 (trademark of Cabot Corporation) (a nickel-base hardfacing alloy). Other coatings that have been qualified for limited applications include chromium plating for low temperature galling protection and nickel plating for radionuclide trapping.Processes now employed include detonation gun coating, diffusion coating, electrospark deposition coating and electroplating. Several plasma spray processes, sputtering and chemical vapor depositions have been candidates for use on some reactor components, but did not pass the required qualification tests or were not economically competitive with alternative coating methods.     

Influence of experimental parameters on spatial phase distribution in as-sprayed and incubated hydroxyapatite coatings

In the present study, the behavior and properties of plasma-sprayed hydroxyapatite coatings [Ca(10)(PO(4))(6)(OH)(2), HAp] were investigated in relation to the spraying process. The experiments were focused on the influence of type of feedstock and spray power on the phase composition and distribution within the coatings. Depth profiles of the coatings were investigated before and after incubation in revised simulated body fluid (SBF) by X-ray diffraction and infrared spectroscopy. Besides HAp, the coatings contain oxyapatite (OAp) and carbonate apatite (CAp). Additionally, tricalcium phosphate (TCP), tetracalcium phosphate (TTCP), CaO, and an amorphous phase were detected in the coatings. The HAp content directly depends on the used spray powder and spray power, where the influence of spray powder is much higher than the influence of the spray power. The grain size range of the spray powder strongly influences the HAp content in the coating and the formation of CaO. The in vitro behavior of the coatings in simulated body fluid mainly depends on the contents of CaO and amorphous calcium phosphate, respectively. The formation of portlandite due to the reaction of the coating with the SBF is strongly influenced by the porosity of the coatings and can be used as an indicator for the depth of interaction between fluid and coating.     

Cold spraying of Cu‐Al‐Bronze for cavitation protection in marine environments

High strength metal coatings are promising for reducing the cavitation damage of ship rudders. Cold spraying offers the opportunity to produce coatings that have similar properties as respective bulk material. In this study, conditions for cold spraying CuAl10Fe5Ni5 bronze are evaluated for the use at ship rudder applications. The spray parameter sets were varied with respect to nozzle type, process gas pressure and temperature. Single particle impact morphologies were investigated by scanning electron microscopy and categorized into different classes to obtain information on the deformation behavior. Within the selected parameter regime, coatings were processed with deposition efficiencies of up to 70%. The coating microstructures were analyzed by optical microscopy to gain information on spraying conditions for minimum porosity. For the higher parameter sets, porosities of less than 2% were obtained. Coating performance was investigated by cavitation test procedures. These first results show that cold sprayed bronze coatings still faces challenges with respect to powder properties. With further optimization, respective coatings could have a high potential for ensuring a good performance in rudder protection.     

涂层与镀层复合雷达波吸收性能研究

以纳米铁酸镍钴铁氧体复合Co粉、羰基铁粉等为吸收剂,并采用化学镀层和涂层方法,进行了单层、双层和三层沣涂层的吸波性能实验研究.结果表明:双层复合涂层的吸波性能较单层涂层在低频段有较大的提高;三层复合涂层的吸波性能优于双层复合涂层,三层复合涂层反射率小于-5dB的频宽为4.5～18GHz,较双层涂层提高5.4GHz.其中,镀镍层对提高吸波性能作用明显.     

冷喷涂CoNiCrAlY涂层在Na_2SO_4熔盐中的热腐蚀行为

利用冷喷涂技术制备CoNiCrAlY涂层,并对涂层进行了真空预氧化处理。结合X射线衍射,扫描电镜,能谱分析等方法研究预氧化处理前后的CoNiCrAlY涂层在900℃的Na2SO4熔盐中的热腐蚀行为。结果表明:冷喷涂CoNiCrAlY涂层含氧量为0.12%(质量分数),孔隙率小于0.28%(体积分数)。真空预氧化处理在涂层表面生成厚约0.26μm连续、致密的α-Al_2O_3氧化膜;喷涂态涂层和预氧化涂层在热腐蚀150h后表面均生成了以α-Al_2O_3为主的致密连续氧化膜,保护了基体免受腐蚀破坏;真空预氧化处理有效减缓了S和O等元素向涂层内扩散的速率,从而提高了涂层的抗Na2SO4熔盐热腐蚀性能;高温热腐蚀对涂层的破坏作用远大于高温氧化。在相同温度下,涂层在单一Na2SO4熔盐中腐蚀时,Al的消耗速率约为高温氧化时的2倍。     

Fabrication of high hardness and corrosion resistance coatings from Fe-based alloy powders

Gas atomized Fe₅₀Cr₂₄Mo₂₁Si₂B₃ powders were used to form Fe-based alloy coatings by the air plasma spray method. The coatings exhibited high amorphous nature and extremely low porosity of 0.41% in about 200 µm thickness. The Fe-based coating exhibits an average hardness about 1255 Hv. The Fe-based coatings could be potentially applied as functional surface protective coatings.     

Nickel-based wear-resistant coatings by vacuum melting

In various coating processes nickel-based hard alloy powders are applied in either an atomized or a mechanically pulverized form. The coatings show good corrosion resistance, a high abrasion resistance and a relatively low melting point. Since boron is sparingly soluble in nickel, the boride Ni₃B forms a low melting eutectic at about 1000 °C with the nickel solid solution. Boron and silicon act simultaneously as deoxidizers and improve both the properties of the coating and the bonding to the substrate. Diffusion into the substrate occurs during the coating procedures.In this paper we discuss the behaviour of heterogeneous powder compounds with nickel hard alloys. For many applications mixtures with various carbides are used. During coating, reactions take place between the Ni-Cr matrix and the added carbides. These heterogeneous or quasi-alloys, which are used because of their abrasion resistance, are metastable.The abrasion resistance depends primarily on the phases as well as on their grain size, the grain size distribution and alterations to the matrix. When carbidic quasi-alloys are exposed to abrasion and corrosion at high temperatures, reactions of the existing phases during use cannot be completely excluded. Heat treatment causes changes in the structure and abrasion resistance of carbide-containing quasi-alloys.It is difficult to follow reactions which take place during coating either in the fused mass of quasi-alloys or in heterogeneous compounds. Because of their relatively low melting points nickel-based hard alloys can be coated by furnace melting. Hence carbide compounds with Ni-Cr-B-Si powder alloys are most suitable for research also. In these mechanical alloys segregation, of relevance to practical applications, can be studied as well as the formation of various phases during the coating or heat treatment processes.The behaviour of mixtures of Ni-Cr-B-Si powder alloy with different amounts of a number of carbides is reported. The structures of the resulting phases were studied and we tried to correlate these with the results of our abrasion tests.For tungsten carbide-nickel hard alloy mixtures the formation of the ? phase is influenced by the coating parameters and the matrix as well as by the diffusion of iron from the substrate into the coating.We also investigated mixtures of an Ni-Cr-B-Si matrix with TiC (Ti, W)C and NbC. The wear resistance against steel and SiC was measured. Various wear mechanisms and the properties of the carbide-matrix interface the wear results.