A taguchi experimental design study of twin-wire electric arc sprayed aluminum coatings

An experimental study was conducted on the twin- wire electric arc spraying of aluminum coatings. This aluminum wire system is being used to fabricate heater tubes that emulate nuclear fuel tubes for use in thermal-hydraulic experiments. Experiments were conducted using a Taguchi fractional factorial design parametric study. Operating parameters were varied around the typical process parameters in a systematic design of experiments to display the range of processing conditions and their effect on the resultant coating. The coatings were characterized by hardness tests, optical metallography, and image analysis. This article discusses coating hardness, roughness, deposition efficiency, and microstructure. The study attempts to correlate the features of the coatings with the changes in operating parameters. A numerical model of the process is presented, including gas, droplet, and coating dynamics.     

In-flight oxidation of aluminum in the twin-wire electric arc process

This paper examines the in-flight oxidation of aluminum sprayed in air using the twin-wire electric arc (TWEA) thermal spray process. Aerodynamic shear at the droplet surface increases the amount of in-flight oxidation by promoting entrainment of the surface oxides within the molten droplet and continually exposing fresh fluid available for oxidation. Mathematical predictions herein confirm experimental measurements that reveal an elevated, nearly constant surface temperature (∼2273 K) of the droplets during flight. The calculated oxide volume fraction of a “typical” droplet with internal circulation compares favorably to the experimentally determined oxide content (3.3–12.7%) for a typical TWEA-sprayed aluminum coating sprayed onto a room temperature substrate. It is concluded that internal circulation within the molten aluminum droplet is a significant source of oxidation. This effect produces an oxide content nearly two orders of magnitude larger than that of a droplet without continual oxidation.     

In-Flight particle measurements of twin wire electric arc sprayed aluminum

A real-time, nonintrusive measurement technique was successfully applied to a Tafa Model 9000 (TAFA Incorporated, Concord, NH) twin wire electric arc thermal spray system to simultaneously measure particle size, velocity, and temperature within the spray plume. Aluminum wire was sprayed with the current varied from 100 to 300 amp, and the gun pressure (air flowrate) varied from 40 to 75 psia. For all cases, the average sizes of the molten aluminum particles along the spray centerline range from 33 to 53 μm. The particles accelerate to peak velocities between 130 and 190 m/s, then decelerate slightly as they travel downstream. The average centerline particle temperature ranges from 2004 to 2056 °C, and the temperature profile remains fairly flat throughout transport to the substrate. A stagnation pressure probe was used to quantify the gas flow regime in the unladen jet. The wires were found to have a pronounced effect on the flow, resulting in a complex three-dimensional flowfield with mixed regions of subsonic and supersonic flow.     

Steel cathodic protection afforded by zinc, aluminium and zinc/aluminium alloy coatings in the atmosphere

Zinc has traditionally been the metallic material most widely used to protect steel against atmospheric corrosion due to its ability to afford cathodic protection to steel in all types of natural atmospheres. In recent decades, aluminium and zinc/aluminium alloy coatings have been used instead of zinc in certain atmospheric applications. Although these coatings present some advantages over zinc, they are not able to cathodically protect steel substrates in all types of natural atmospheres. The present paper assesses the cathodic protection afforded by Al (flame spraying), Al/13 Si (hot dipping), 55Al/Zn (hot dipping), Zn/15Al (flame spraying), Zn/5Al (hot dipping), Zn (hot dipping), Zn (discontinuous hot dipping) and Zn (electroplating). Aluminium and aluminium-rich alloy coatings (55%Al/Zn) provide cathodic protection to the steel substrate only in atmospheres that are highly contaminated with chloride ions (>100 mg Cl⁻ m⁻² day⁻¹) where these coatings become active.     

镁合金表面电弧喷涂铝涂层在氯离子中的腐蚀行为

采用电弧喷涂技术在镁合金AZ91基材表面制备铝涂层.通过5(质量分数,%)NaCl溶液浸泡试验和盐雾试验,考察了镁合金表面铝涂层在氯离子中的耐蚀性能及其腐蚀行为.利用光学显微镜、扫描电子显微镜(SEM)和X射线衍射仪(XRD)分析技术对涂层形貌、显微组织结构和相组成进行了研究.结果表明,封孔处理后的试样耐蚀性能有较大提高,未封孔的涂层试样腐蚀比原始镁合金更严重.     

电弧喷涂铝青铜复合涂层的抗高温氧化作用与机理

采用铝青铜底层,外加厚度为0.1～0.2 mm的纯铝涂层可进一步地提高涂层体系的抗氧化性能.900 ℃加热12 h的10次循环氧化试验结果表明,纯铝层的应用有助于提高铝青铜涂层的自封孔能力,在涂层表面形成的增厚富铝氧化膜以及在涂层基体界面上形成的富铝氧化层都对钢铁基体的防护有利.复合涂层体系与试件基体结合可靠,没有早期失效迹象,是一种有希望的高温防护涂层体系.     

铝合金表面电弧喷涂铝涂层工艺与性能

采用电弧喷涂工艺在6061铝合金基体表面喷涂高纯铝涂层,利用金相显微镜对涂层的组织进行观察,分析了基体与涂层的结合方式,测量了涂层的孔隙率.并采用质量分数为5%的NaCl溶液浸泡试验、盐雾试验和电化学试验,检验了涂层的耐腐蚀性.结果表明,利用电弧喷涂技术可以在6061铝合金基体表面形成均匀、致密、孔隙率低、结合良好的高纯铝涂层;高纯铝涂层耐腐蚀性较好,对铝合金基体起到了保护作用,涂层经过封孔工艺处理后保护作用更好.     

LY12铝合金三价铈盐溶液中成膜工艺

利用浸渍法在LY12铝合金表面获得了金黄色的铈转化膜, 确定了常温稀土(铈)化学转化膜成膜工艺. 应用电化学方法和浸泡试验研究了铝合金铈化学转化膜的成膜动力学及转化膜在3.5%NaCl溶液中的耐蚀性能, 并与传统的Alodine处理工艺进行了比较. 采用表面分析技术分析了膜的成分并观察了膜的微观形貌. 结果表明, 本稀土处理工艺成膜工艺简单, 成膜速度快, 耐蚀性能略优于Alodine转化膜, 能有效地抑制铝合金的点腐蚀. SEM表明铝合金铈转化膜由许多球形颗粒和块状膜构成. EDAX能谱表明, 铈转化膜主要含有铈、氧和铝3种元素, 球形颗粒含有较高浓度的氧和铈.     

电弧喷涂FT45涂层与Ni60喷焊涂层组织性能研究

研究了电弧喷涂FT45涂层与Ni60喷焊涂层的微观组织性能，对比分析了它们在高温腐蚀磨损条件下的使用性能。结果表明Ni60喷焊层、FT45电弧喷涂层都具有较高的硬度、较好的耐磨性。尤其是Ni60喷焊层具有很高的硬度和优异的耐磨性。2种镍基涂层都具有优良的耐高温腐蚀能力。     

Wear and corrosion properties of plasma sprayed AI2O3 and Cr2O3 coatings sealed by aluminum phosphates

Plasma-sprayed aluminum oxide (AI₂O₃) and chromium oxide (Cr₂O₃) coatings were sealed by aluminum phosphates. Phosphates were formed throughout the coating, down to the substrate, and were verified by scanning electron microscopy and hardness measurements. The sealing increased the hardness of the coatings by 200 to 300 Vickers hardness (HV) units. Abrasion and erosion wear resistances were increased by the sealing treatment. Sealing also substantially closed the open porosity, as shown in electro-chemical corrosion tests. The sealed structures had good resistance against corrosion during 30 days of immersion in both acidic and alkaline solutions with pH values from 0 to 10. No decrease in abrasion wear resistance was observed after immersion.     

等离子喷涂Al_2O_(3p)/NiCrBSi涂层优化设计

利用二次回归正交组合设计法优化喷涂工艺参数,建立了等离子喷涂Al2O3p/NiCrBSi复合材料涂层冲蚀磨损失重率的二次回归方程.研究了等离子喷涂参数对涂层冲蚀磨损失重率的影响.结果表明,利用Matlab软件编程计算,优化等离子喷涂参数,明显提高了涂层的抗冲蚀磨损性能.为等离子喷涂制备以氧化铝(Al2O3)颗粒增强金属基(NiCrBSi)复合材料涂层(Al2O3p/NiCrBSi)的实际应用提供必要的理论依据和技术数据.     

含有金属黏结相的热喷涂WC涂层在盐雾中的腐蚀行为

研究黏结相化学成分对涂层材料的耐盐雾腐蚀性能的影响,对采用超音速火焰喷涂制得的WC?17Co和WC?10Co?4Cr涂层进行电化学试验和长时间的盐雾腐蚀实验(浓度为5%的NaCl溶液,温度35°C)。结果表明：WC?10Co?4Cr涂层的耐盐雾腐蚀性能优于WC?17Co涂层。对于WC?17Co涂层,主要腐蚀行为除了粘结金属的腐蚀外还包括WC颗粒与粘结相金属之间发生的微点偶腐蚀;对于WC?10Co?4Cr涂层,形成的氧化物有利于抑制金属相与粘结相的腐蚀。说明金属材料成分是影响超音速火焰喷涂WC基涂层耐盐雾腐蚀性能的重要因素之一。     

Effect of heat treatment on the intermetallic layer of cold sprayed aluminum coatings on magnesium alloy

Dense and thick pure aluminum coatings were deposited on AZ91D-T4 magnesium substrates using the cold spray process. Heat treatments of the as-sprayed samples were carried out at 400 °C using different holding times. The feedstock powder, substrate and coating microstructures were examined using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) as well as Vickers microhardness analysis. The results demonstrate that aluminum coatings having dense and uniform microstructure can be deposited successfully using a relatively large feedstock powder. It has been identified that the intermetallics Al₃Mg₂ (γ phase) and Mg₁₇Al₁₂ (β phase) were formed at the coating/substrate interface during heat treatment. The growth rate of these intermetallics follows the parabolic law and the γ phase has a higher growth rate than the β phase. The thickness of the Mg₁₇Al₁₂ and Al₃Mg₂ intermetallic layers has reached 83 μm and 149 μm, respectively. This result is almost 45% higher than what has been reported in the literature so far. This is attributed to the fact that T4 instead of as cast Mg alloy was used as substrate. In the T4 state, the Al concentration in the Mg matrix is higher, and thus intermetallic growth is faster as less enrichment is required to reach the critical level for intermetallic formation in the substrate. The AZ91D-T4 magnesium substrate contains single α phase with fine clusters/GP-zones which is considered beneficial for the intermetallic formation as well as the intimate contact between the coating/substrate interface and the deformed particles within the coating.     

HVOF/AC-HVAF热喷WC-10Co-4Cr涂层的耐冲蚀性能

采用高速火焰热喷涂系统（HVOF/AC-HVAF）在0Cr13Ni5Mo不锈钢表面制备了三种组织结构不同的WC-10Co-4Cr涂层,通过料浆罐冲蚀试验机对三种涂层和0Cr13Ni5Mo基材的冲蚀行为和冲蚀机制进行了研究,重点分析涂层组织与耐冲蚀性能的关系. 结果表明,三种涂层的耐冲蚀性能均优于0Cr13Ni5Mo基材,冲蚀失重仅为基材的6% ~ 35%,组织越均匀、致密的涂层耐冲蚀性能越优. 低攻角冲击时,涂层冲蚀机制以粘结相去除,WC颗粒剥落为主,基材冲蚀机制主要为微切削;高攻角冲击时,涂层冲蚀机制以涂层剥落为主,基材的冲蚀机制主要为变形磨损. 涂层的组织决定了不同试验条件下涂层的冲蚀行为和冲蚀机制.     

Characteristics of arc plasma deposited TiAlZrCN coatings

TiAlZrCN superhard coatings, in which Ti and Al were additions to ZrCN base compound, were prepared by the cathodic arc method. The films were deposited on Si, plain carbon steel and high-speed steel substrates in a mixture of N₂ and CH₄ gases. Elemental and phase composition, chemical bondings, texture, surface roughness, hardness, adhesion, tribological characteristics and erosive–corrosive resistance were investigates as a function of gas composition and total gas flow rate, using XPS, GDOES and XRD techniques, surface profilometry, microhardness and scratch adhesion measurements, tribological and erosive tests. It was shown that the properties and performance of the coatings were strongly dependent on the CH₄/(CH₄ + N₂) flow rate and also on the total gas flow. The tribological and anti-erosive characteristics of the TiAlZrCN coatings were found to be superior to those of reference films (ZrN, ZrC, ZrCN, and TiAlCN). Maximum hardness values (42–45 GPa) were obtained for the films prepared at CH₄/(CH₄ + N₂) ratios ranging from 0.2 to 0.4.     

Influence of silane on corrosion resistance of magnesium alloy AZ31 with thermally sprayed aluminum coatings

Aluminum coatings on Mg alloy AZ31 were fabricated using the thermal spraying technique, and then sealed with silane.The surface morphology and chemical groups were discerned using scanning electron microscopy and examined using Fourier transformation infrared spectroscopy, respectively.The salt fog tests and the potentiodynamic electrochemical technique were applied to evaluate the influence of silane on corrosion of the AZ31 alloy with aluminum coatings.The results showed that the corrosion resistance of ...     

Preparation and characterization of Ce-silane-ZrO2 composite coatings on 1060 aluminum

In order to improve the property of traditional Ce-based conversion coatings, Ce-silane-ZrO₂ composite coatings were successfully prepared on 1060 aluminum. The microstructure, chemical element composition and corrosion resistance of Ce-based conversion coatings and Ce-silane-ZrO₂ composite coatings were investigated by SEM, AFM, XPS and EIS analyses. Stacking structure of the composite coating can be observed. The inner layer of the composite coatings mainly consists of oxide and hydroxide of Ce(III), and the silane network is composed of the outer layer together with a small amount of Ce(IV) hydroxide. By adding silane and ZrO₂ nanoparticles into Ce-based conversion coatings, the porosity and the micro cracks of the coatings decrease apparently accompanying with the improvement of the corrosion resistance.     

热加工对冷喷涂铝合金块材性能的影响

为了提高冷喷涂增材制造铝基块材性能,对低压冷喷涂法沉积的7075铝合金块材进行了后续退火和热轧加工。采用光学显微镜和扫描电镜观察试样的组织结构特征,并通过拉伸试验和电化学测试表征了块材的应力-应变曲线和耐蚀性。结果表明,低压冷喷涂法沉积的铝合金块材结构上存在大量的颗粒界面和少量微孔等缺陷,拉伸时发生脆性断裂,塑性很差,耐点蚀性能差;经过400℃退火4 h后,结构缺陷显著减少;再经过30%压下量的热轧加工后,结构更加致密,强度和韧性均提高,耐蚀性也随着结构缺陷的减少而提高。     

The corrosion behavior and microstructure of high-velocity oxy-fuel sprayed nickel-base amorphous/nanocrystalline coatings

The corrosion characteristics of two Ni-Cr-Mo-B alloy powders sprayed by the high-velocity oxy-fuel (HVOF) process have been studied using potentiodynamic and potentiostatic corrosion analysis in 0.5 M H₂SO₄. The deposits were also microstructurally characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM) (utilizing both secondary electron and backscattered electron modes), and transmission electron microscopy (TEM). Results from the microstructural examination of the two alloys have revealed a predominantly amorphous/nanocrystalline face centered cubic (fcc) matrix containing submicron boride precipitates as well as regions of martensitically transformed laths. Apparent recrystallization of the amorphous matrix has also been observed in the form of cellular crystals with a fcc structure. The oxide stringers observed at splat boundaries were found to be columnar grained α-Cr₂O₃, though regions of the spinel oxide NiCr₂O₄ with a globular morphology were also observed. The coatings of the two alloys exhibited comparable resistance to corrosion in 0.5 M H₂SO₄, as revealed by potentiodynamic tests. They both had rest potentials approximately equal to −300 mV saturated calomel electrode (SCE) and passive region current densities of ∼1 mA/cm². Microstructural examination of samples tested potentiostatically revealed the prevalence of degradation at splat boundaries, especially those where significant oxidation of the deposit occurred. This paper originally appeared in Thermal Spray: Meeting the Challenges of the 21st Century; Proceedings of the 15th International Thermal Spray Conference, C. Coddet, Ed., ASM International, Materials Park, OH, 1998. This proceedings paper has been extensively reviewed according to the editorial policy of the Journal of Thermal Spray Technology.     

AA6063铝合金表面激光熔覆TiC/Al_3 Ti复合材料涂层

将Al、Ti和TiC 粉末预涂在AA6063铝合金表面,采用激光熔覆法制备了TiC/Al_3Ti复合材料涂层,分析了激光熔覆层的显微组织和硬度分布.结果表明,采用合适的激光工艺可获得无裂纹和孔洞且表面平整的熔覆层.熔覆层由枝晶状Al_3Ti、枝晶间α-Al和均匀分布的TiC颗粒组成,TiC颗粒在激光辐照过程中未发生熔解,熔覆层与基材的界面结合良好.随与熔覆层表面距离的增加,Al_3Ti枝晶的尺寸变大,α-Al的含量减少.激光熔覆层的硬度可达700 HV0.2,显著改善了AA6063铝合金的表面硬度.