Microstructure and mechanical properties of twin-wire arc spraying Ni-Swt.% AI coating on 6061-T6 aluminum alloy

Thermal sprayed Ni-5wt.% Al coating was fabricated on the substrate of 6061-T6 aluminum alloy by twin-wire arc spraying. Experimental results indicated that the average value of bond strength was around 46. 90 MPa, the average hardness was 240 HV and the average value of surface roughness was about O. 14 mm. Friction and wear test results showed that the dry friction coefficient of Ni-5wt.% Al coating firstly decreased, and then tended to a slight increase after 200 cycles. In the early abrasion stage, adhesion wear played the key role for wear mechanics of Ni-5wt.% Al coating, but gradually abrasive wear became to replace adhesion wear.

Computer simulation to arc spraying

The arc spraying process is divided into two stages: the first stage is atomization-spraying stream (ASS) and the second one is spraying deposition (SD). Then study status is described of both stages’ physical model and corresponding controlling-equation. Based on the analysis of study status, the conclusion as follows is got. The heat and mass transfer models with two or three dimensions in ASS stage should be established to far deeply analyses the dynamical and thermal behavior of the overheat droplet. The statistics law of overheated droplets should be further studied by connecting simulation with experiments. More proper validation experiments should be designed for flattening simulation to modify the models in SD stage.

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.

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.

Effect of chromium on hot corrosion behavior of arc-sprayed NiCr coatings

In this article,NiCr coatings with chromium content of 13%,27%and 41%were prepared by arc spraying.They were exposed in molten salts(NaCl-Na_(2)SO_(4))at 800℃for 200 hours.The effect of chromium content on the hot corrosion behavior of the coatings was in-vestigated.X-ray diffraction(XRD)and scanning electron microscope with energy dispersion spectrum(SEM-EDS)were used to analyze the phase compositions,morphologies and chemical compositions of the coatings.The results show that NiCr13 coating exhibited the worst hot corrosion resistance due to the low chromium content,which resulted in NiO being the major reaction product.It should be noted that the hot corrosion resistance of NiCr27 coating was better than that of NiCr41 coating.The basic fluxing of Cr_(2)O_(3) lowered its protection during the hot corrosion process and led to the formation of porous Cr_(2)O_(3) on the NiCr41 coating.The molten salts accelerated the oxidation reac-tion resulting in thicker and porous oxide scales formed on the surfaces of coatings.

Research on automatic high velocity arc spraying technique and metastable coating materials

Into the 21st century, remanufacturing engineering has been accepted by more and more people in China. Remanufacturing is an industrial maintenance technology for worn or waste electro-mechanical products using advanced technology, which means the high-level stage for the maintenance and surface engineering. In this paper, a new automotive high velocity arc spraying system was introduced. And three kinds of advanced amorphous and nanocrystalline metastable coatings were developed, including Fe, Ni and Al-based amorphous and nanocrystalline composite coatings. Their research development and applications were introduced. And the development trends of high velocity arc spraying system and advanced metastable surface protective coating materials on the remanu- facturing engineering were indicated.

Microstructure characterization and mechanical properties of thermal sprayed Ni-20wt. % Al coating

Thermal sprayed Ni-20wt. % Al coating is fabricated on 6061-T6 aluminum alloy substrates by twin-wire arc spraying （TWAS）. Experimental results present that the average bonding strength is around 53 MPa and the average hardness reaches 325 HV. The Vickers microhardness of NiAl and Ni3Al intermetaUic compounds is larger than that of the substrate, which is beneficial for improving the wear property. Wear mechanism exhibits features of adhesive wear. Friction and wear test results indicate that the wet friction coefficient is higher than the coefficient of dry friction after 200 cycles, and variations of the wet friction coefficient are relatively smaller.

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.

Experimental and modeling studies on installation of arc sprayed Zn anodes for protection of reinforced concrete structures

Arc sprayed zinc （Zn） anode on concrete surfaces has been an emerging technology for protecting reinforced concrete structures from rebar corrosion in coastal environments. Many cathodic protection （CP） systems with arc sprayed Zn anodes will reach or exceed their design life in the near future and thus may function improperly or insufficiently, making it necessary to replace the aged anodes. However, prior to this study, little was known about the most effective profile for the concrete surface, for either new concrete or old concrete with existing Zn anodes removed. This work develops criteria to properly prepare the concrete surface before the application of new Zn anode. Experimental studies were conducted both in the laboratory and for a field structure in Oregon. Artificial neural network was used to achieve better understanding of the complex cause-and-effect relationships inherent in the Zn-mortar or Zn-concrete systems and was successful in finding meaningful, logical results from the bond strength data. The goal is to achieve strong initial bond strength of new Zn to concrete, which is essential for long-term performance of the CP system. The results from this case study suggest that it is necessary to adjust the anode removal and surface sandblasting based on the electrochemical age of the existing concrete. In all cases of sandblasting, minimize the exposure of large aggregates （e.g., those bigger than 19 mm in diameter）.

Influence of silicon coating on the corrosion resistance of Zn-Al-Mg-RE-Si alloy

The electric arc spraying method was used to prepare the Zn-Al-Mg-RE-Si alloy coating with different content of silicon.The corrosion resisting property was measured by copper accelerated salt spray(CASS) and corrosion weightless test.The influence of silicon content on the corrosion resisting property was investigated by XRD,SEM,polarization curve and electrochemical impedance spectroscopy(EIS) and the electrochemical property of coating in the corrosion process was analyzed.The results showed that the density of coating was improved significantly since the major nonequilibrium glass-like state phase was composed of silicon and other metals existed in the Zn-Al-Mg-RE-Si alloy coating,which prevented the corrosive medium and retarded the corrosion velocity because of compact corrosion products in the corrosion embryo.The Zn-Al-Mg-RE-Si coating had better corrosion resistance than the Zn-Al-Mg-RE because of more positive potential,half corrosion current density and double electrochemical reaction resistance.