Configuration optimization of high velocity arc spraying gun

In order to improve the in-flight characteristics of the atomizing droplets during high velocity wire arc spraying (HVAS), some changes have been operated on the original design of the HVAS gun configuration. A comparative study was carried out to investigate the microstructure and properties of the coatings produced by the original design spraying gun and the modified one, using 3Cr13 wires of 3 mm in diameter. The characteristics of their jets were examined during spraying. The results indicate that, the included angle between the two wires and the distance from the nozzle to the meeting point of the two vires may have a strong influence on the characteristics of the in-flight droplets and then the coatings. The jet divergence is found to be lower than that of the original one (about 12° against 25°). By modified gun, the adhesion strength, the microhardness and porosity of the coating deposited by modified gun are increased by 39% and 9% respectively. And the porosity of the coatings is decreased by 57%.

Structure and sliding wear behavior of 321 stainless steel/Al composite coating deposited by high velocity arc spraying technique

A typical 321 stainless steel/aluminum composite coating (321/Al coating) was prepared by high velocity arc spraying technique (HVAS) with 321 stainless steel wire as the anode and aluminum wire as the cathode. The traditional 321 stainless steel coating was also prepared for comparison. Tribological properties of the coatings were evaluated with the ring-block wear tester under different conditions. The structure and worn surface of the coatings were analyzed by scanning electron microscopy(SEM), X-ray diffractometry(XRD) and energy dispersion spectroscopy(EDS). The results show that, except for aluminum phase addition in the 321/Al coating, no other phases are created compared with the 321 coating. However, due to the addition of aluminum, the 321/Al coating forms a type of "ductile/hard phases inter-deposited" structure and performs quite different tribological behavior. Under the dry sliding condition, the anti-wear property of 321/Al coating is about 42% lower than that of 321 coating. But under the oil lubricated conditions with or without 32 h oil-dipping pretreatment, the anti-wear property of 321/Al coating is about 9% and 5% higher than that of 321 coating, respectively. The anti-wear mechanism of the composite coating is mainly relevant to the decrease of oxide impurities and the strengthening action resulted from the "ductile/hard phases inter-deposited" coating structure.

Heat transfer analysis of atomized droplets during high velocity arc spraying

The heat transfer problem of the atomized droplets during high velocity arc spraying (HVAS) was modeled and solved by a numerical method using a Fe-Al alloy, and the influences of several important process parameters on the heat transfer behaviors of the atomized droplets were analyzed. The results show that the initial cooling rates of different size droplets range from 105 to 107 K/s, thus producing the coating microstructure with the features of rapid solidification. The droplet size, atomization gas pressure and droplet superheat have great influences on the heat transfer behavior of the droplet. The droplet temperature and cooling rate are much sensitive to the droplet sizes, but insensitive to the atomization gas pressure and droplet superheat. It can be predicted that the properties of HVAS coatings will be improved by decreasing droplet size as well as increasing atomization gas pressure and droplet superheat in certain extents.

Oxidation performance of Fe-Al/WC composite coatings produced by high velocity arc spraying

Fe-Al intermetallics with remarkable high-temperature intensity and excellent erosion, high-temperature oxidation and sulfuration resistance are potential low cost high-temperature structural materials. But the room temperature brittleness induces shape difficult and limits its industrial application. The Fe-Al intermetallic coatings were prepared by high velocity arc spraying technology with cored wire on 20G steel, which will not only obviate the problems faced in fabrication of these alloys into useful shapes, but also allow the effective use of their outstanding high-temperature performance. The Fe-Al/WC intermetallic composite coatings were prepared by high velocity arc spraying technology on 20G steel and the oxidation performance of Fe-Al/WC composite coatings was studied by means of thermogrativmetic analyzer at 450, 650 and 800℃. The results demonstrate that the kinetics curve of oxidation at three temperatures approximately follows the logarithmic law. The composition of the oxidized coating is mainly composed of Al2O3, Fe2O3, Fe3O4 and FeO. These phases distribute unevenly. The protective Al2O3 film firstly forms and preserves the coatings from further oxidation.

Study on microstructure and properties of high velocity arc sprayed Fe_3Al intermetallic coating

Coating structural materials with Fe 3Al based intermetallics may rapidly lead to industrial application of their environment and wear resistant features. In the present study, high velocity arc spraying (HVAS) was used to in situ synthesize Fe 3Al intermetallic coating. The microstructural characterization and properties of the coating have been investigated. The microstructure was found to consist of Fe 3Al based intermetallic (D0 3 and B2) and α Fe regions together with fine oxide (α Al 2O 3) layers. TEM images of coating show that the solidified lamellae are polycrystalline and have a grain size of the order of about 150 nm , and there also exists amorphous state in some areas. It can be concluded that a very high cooling rate has been obtained during HVAS process. Moreover, the coating has relatively higher adhesion strength and microhardness, as well as lower density and porosity.

Wear behavior of high velocity arc sprayed 3Cr13 steel coating in oil containing sand

To improve the wear resistance of the machine components serving in desert areas, the 3Cr13 stainless steel coating was produced by the high velocity arc spraying technique. The microstructure and phase constitute of the coating were analyzed by SEM and XRD. The effects of sand content on the friction and wear behaviors of the coating under the lubrication of oil containing sand were investigated on a ball-on-disk tester. SEM was used to reveal the wear mechanisms of the coating. The results show that the wear volume increases with increasing the sand content in the oil, and the sprayed coating exhibits better triobological properties compared with the 1045 steel. The predominant wear mechanisms of the sprayed coating are micro-cutting, brittle fracture and delamination.

Sliding wear behavior of high velocity arc sprayed Fe-Al coating

The friction and wear behavior of Fe Al intermetallics based coating produced by high velocity arc spraying technique under dry sliding at room temperature were investigated using a ball on disc tribotester. The effect of sliding speed on friction coefficient and wear of the coating was studied. The worn surface of the coating was analyzed by scanning electron microscope (SEM) to explore sliding friction and wear mechanism. The results show that the variations of friction coefficient can be divided into three distinct steps during the trail. Both the friction coefficient and the wear of the coating increase with increased sliding speed due to accelerated crack propagation rate and lamellar structure with poor ductility of the coating. The coating surface is subjected to alternately tensile stress and compression stress during sliding wear process, and the predominant wear mechanism of the coatings appears to be brittle fracture and delamination.

Erosion-Corrosion Behaviors of High Velocity Arc Sprayed Fe-AlCr_3C_2 Coating

Iron aluminide intermetallic coatings were prepared from Fe-Al/Cr3C2 cored wires using High Velocity Are Spraying （ HVAS ） technology. Erosion and corrosion properties of HVAS sprayed Fe-Al/Cr3C2 coatings were investigated. Results show that the erosion at impingement angle of 30°is more than that of 90°. The erosion resistance of coatings was enhanced uith the inereaase of temperature. Coatings had a better erosion resislance than substrwles. The erosion changed from ductile behariors to brittle behaviors above 450℃ . At high temperature, the erosion resistances were superior to those at low temperwlure and roonl temperwlure. Cowlings had much higher corrosion properties than substrates. The temperature had a little effect on the corrosion resistance of coatings ; The corrosion losing of cowlings increased slowly with the increase of corrosion time. The HVAS-sprayed Fe-Al/Cr3C2 coatings exhibited a high bond strength and hardness.

Abrasive wear behaviors of high velocity arc sprayed iron aluminum composite coatings

The High Velocity Arc Spraying （HVAS） technology was used to prepare Fe-Al composite coatings by the adding of different elements into cored wires to obtain different Fe-Al coatings. The added compounds do great effect on the properties of the composite coatings. The microstructures and abrasive wear performances of the coatings were assessed by transmission electron microscopy （TEM）, scanning electron microscopy （SEM）, and THT07-135 high temperature wear equipment. It was found that the adding of Cr3C2 can greatly increase the room temperature wear behavior, and Fe-Al/WC coatings have adapting periods at the beginning of wear experiment. With the rise of temperature, the wear resistance of Fe-AI/Cr3C2 coatings becomes bad from room temperature to 250℃, and then stable from 250℃ to 550℃; the wear resistance of Fe-Al/WC becomes well with the rise of temperature. The adding of Cr and Ni can also improve wear performances of Fe-Al composite coatings.

Tribological properties of high velocity arc sprayed Fe-Al based composite coatings at elevated temperature

Fe-Al based intermetallic composite coatings were in-situ synthesized using Fe-Al/Cr3C2 or Fe-Al/WC cored wires and high velocity are spraying (HVAS) technology. The tribological properties of the Fe-Al based intermetallic composite coatings were investigated using a ball-on-disc tribotester from room temperature to 650 ℃. The results show that the coatings have relatively high bond strength and micro-hardness. The tribological properties of Fe-Al/Cr3C2 and Fe-Al/WC composite coatings were further analyzed and compared. Low and stable wear rates of the Fe-Al based intermetallic composite coatings were indicated from room temperature to 650 ℃. The excellent wear resistance of the composite coatings in high temperature was discussed.

HVAS铁铝粉芯丝材的研制与性能分析

采用高速电弧喷涂技术,结合添加了增强相的铁铝粉芯丝材原位合成了铁铝金属间化合物涂层;阐明了粉芯丝材在高速电弧喷涂技术应用中的优点;探讨了对粉芯丝材的研制所要涉及的直径以及增强相的添加等问题;研究了高速电弧喷涂铁铝金属间化合物涂层性能。结果表明,使用Fe-Al/Cr3C2粉芯丝材得到的高速电弧喷涂涂层具有比Fe-Al/WC涂层更好的结合强度,主要原因是增强相所起的作用不同。

Effect of Al content on high temperature erosion properties of arc-sprayed FeMnCrAl/Cr_3C_2 coatings

Three types of FeMnCrAl/Cr3C2 coatings with different AI content were deposited on 20# steel substrates by the high velocity arc spraying （HVAS） process. Surface microstructures of the coatings were analyzed by optical microscopy （OM） and X-ray diffractometry （XRD）. High temperature erosion （HTE） tests were performed in an erosion tester at different impact angles. The surface morphologies of the eroded coatings were observed on a field emission scanning electron microscope（FE-SEM）. The laminated structure is found on all the prepared coatings with the porosity and oxide fraction in the coatings decreasing with the Al content from 0 to 15% （mass fraction）. Sample FA3 with 15% Al, possessing the lowest porosity and oxide fraction, has the best HTE resistance, which demonstrates that Al addition can improve the HTE resistance of the coatings. The erosion rate of sample FA1 exhibits a maximum value at 90° impact angle. The maximum erosion rates of both FA2 and FA3 samples appear in the range of 60°-90° impact angles. Erosion loss of the coatings occurs through brittle breaking, cutting and fatigue spalling.

High Velocity Arc Spraying for Automotive Industry

A diesel engine crankshaft is failed in journal and the dominant failure mechanism is wear.A 6R robot-based automatic high velocity arc spraying system was developed in this study.The remanufacturing process of engine crankshaft was designed based on the newly developed automatic spraying system and the FeAlNbB cored wire.The two spraying way planning were designed.The results of industrial application in miniature show that,both of the main shaft journal and the crank journal of the crankshaft can be deposited of coating in only one procedure using the developed automatic spraying technology,and a reliable quality remanufactured part was obtained.A comparative evaluation shows that the improvement process offers several benefits.Such as,the coating bond strength and spray rates are all highly increased;the remanufactured cost and time are decreased.Furthermore,this technology has several advantages such as energy and material saving,and environmental protecting,a wide application foreground for this technology is therefore performed.

Electrochemical corrosion behavior of arc sprayed Zn-Al coatings

Cored wires and high velocity arc spraying (HVAS) technique were applied to produce high Al content Zn-Al alloy coatings on low carbon steel substrates. The electrochemical corrosion behaviors of Zn, Al and Zn-Al coatings were studied with potentiodynamic measurement in 5 % NaCl solution. Compared with pure Zn, pure Al and Zn-15Al coatings, Zn-26Al coatings show a higher corrosion resistance in salt solution. The potentiodynamic polarization tests show that the corrosion resistance of Zn-Al coatings increases as Al content is raised. Pure Al coating exhibits different electrochemical behaviors with other coatings. The corrosion initiated at the micro-pores of the coating and the underlying corrosion mechanism is very similar to that of the pitting corrosion.

High Velocity Electric Arc Sprayed Fe-Al-Nb-B Composite Coating and Its Wear Behavior

A type of Fe-Al-Nb-B cored wire was designed and the coating was prepared using a robot-based electric wire arc spraying process. The Fe-Al binary cored wire and coating were also prepared as comparison. The phase composition and structure of the coatings were investigated using X-ray diffraction （XRD）, scanning electron microscopy （SEM） coupled with energy dispersive X-ray spectroscopy （EDS） and transmission electron microscopy （TEM）. The coating tribological properties were evaluated with the micromotion wear tester under different conditions. The results show that, although typical lamellar structure was performed for both the arc sprayed Fe-Al-Nb-B coating and Fe-Al coating, the structure composition, mechanical and wear properties of the former are quite different from those of latter. The Fe-Al-Nb-B coating is a typical composite coating, which is distributed inhomogeneously with α-Fe crystalline, FeAl and Fe3Al intermetallics, amorphous and nanocrystallines as well as locally existed oxide phases. As a result, the mircrohardness and wear resistance of the Fe-Al-Nb-B composite coating increased significantly. Finally the mechanism of the coating wear resistant behavior was discussed based on the experimental results such as friction coefficient, two dimensional and three dimensional worn surface profiles.

High-Temperature Corrosion of Protective Coatings for Boiler Tubes in Thermal Power Plants

High-temperature corrosion is a serious problem for the water-wall tubes of boilers used in thermal power plants. Oxidation, sulfidation and molten salt corrosion are main corrosion ways.Thereinto, the most severe corrosion occurs in molten salt corrosion environment. Materials rich in oxides formers, such as chromium and aluminum, are needed to resist corrosion in high-temperature and corrosive environment, but processability of such bulk alloys is very limited. High velocity electric arc spraying (HVAS) technology is adopted to produce coatings with high corrosion resistance. By comparison, NiCr (Ni-45Cr-4Ti) is recommended as a promising alloy coating for the water-wall tubes, which can even resist molten salt corrosion attack. In the study of corrosion mechanism, the modern material analysis methods, such as scanning electron microscopy (SEM), X-ray diffractometry (XRD) and energy dispersive spectrometry (EDS), are used. It is found that the corrosion resistances of NiCr and FeCrAI coatings are much better than that of 20g steel, that the NiCr coatings have the best anti-corrosion properties, and that the NiCr coatings have slightly lower pores than FeCrAI coatings.It is testified that corrosion resistance of coatings is mainly determined by chromium content, and the microstructure of a coating is as important as the chemical composition of the material. In addition, the fracture mechanisms of coatings in the cycle of heating and cooling are put forward. The difference of the thermal physical properties between coatings and base metals results in the thermal stress inside the coatings. Consequently, the coatings spall from the base metal.

高速电弧喷涂Fe基非晶涂层的晶化行为及其电化学腐蚀特性

利用高速电弧喷涂技术制备了FeNiCrBSiNbW非晶涂层,随后对其进行了不同温度的晶化处理;探讨了Fe基非晶涂层的晶化行为及其对电化学腐蚀特性的影响规律。采用X射线衍射仪、扫描电镜、差示扫描量热仪、电化学工作站对不同温度晶化处理后涂层的组织结构和电化学腐蚀行为进行表征。结果表明:随晶化处理温度的升高,FeNiCrBSiNbW非晶涂层的非晶相含量与孔隙率逐渐降低,涂层在3.5 wt%NaCl溶液中的耐腐蚀性逐渐下降,喷涂态涂层中高的非晶相含量以及低的硼化物含量均有助于其耐腐蚀能力的提升。

新型高速电弧喷涂枪的开发研究

详细介绍了开发研制的新型高速电弧喷涂枪；分析测定了新型喷枪和普通喷枪出口的雾化气流速度，同时采用Al和3Cr13作为对比试验材料，对涂层进行性能研究并观察了其组织结构。结果表明：新型喷枪的雾化气流速度的测试计算值在距枪口80mm的范围内仍然能保持在600m／s左右，比普通喷枪的雾化气流速度有显著地提高；高速电弧喷涂熔融的金属粒子雾化充分，涂层组织致密，层状结构十分明显，并且结合强度值和硬度值均较高：新型高速电弧喷涂论，结构简单，工作性能稳定。高速电弧喷涂是一种优质、高效、低成本的热喷涂方法。

高速电弧喷涂Fe-Al/WC复合涂层的组织和性能

采用粉芯丝材和高速电弧喷涂技术 (HVAS)原位合成了 Fe- Al/WC金属间化合物基复合涂层 ,并研究了涂层的显微组织和性能。结果表明 ,铁铝涂层的成分为 Fe- 1 3.87Al- 1 7.2 7C- 3.35 W- 2 .5 9Ni- 1 .2 7Cr- 1 8.1 4 O (原子分数 ,%) ,主要相是 Fe3 Al,Fe Al和 α- Fe相 ,还有少量 WC,W2 C和 Al2 O3 。TEM观察的涂层的扁平颗粒内是微晶组织 ,在一些区域还发现有非晶组织 ,说明在高速电弧喷涂过程中达到了很高的冷却速度。涂层具有相对较高的结合强度和显微硬度 。