Yongxiong Chen

Numerical Simulation of the Twin-Wire Arc Spraying Process: Modeling the High Velocity Gas Flow Field Distribution and Droplets Transport

During the twin-wire arc spraying, a high velocity gas stream is used to accelerate the arc-melting materials and propel the droplets toward the substrate surface. This study is aimed at investigating the gas flow formation and droplets transport processes using numerical simulation method. Results from the 3-D gas flow field model show that the distribution of the gas flow velocity on the twin-wire intersection plane is quite different from that on the twin-wire vertical plane. Based on the 3-D model, the convergence amplitude of the high velocity zone in the jet center is improved by modifying the gun head design. It is also observed that a flat substrate existed downstream from the gas nozzle exit results in decreasing close to zero in velocity of the gas jet near the substrate. In addition, the predicted droplet trajectories and velocity distributions exhibited good agreement with experimentally observations.

Comparative Study of 321 Stainless Steel and 321-Al Composite Coatings Deposited by Arc Spraying Process

A new type of composite coating (321—Al coating) was prepared by using the 321 austenitic stainless steel wire feed stock as the anode and aluminum wire as the cathode in arc spraying process. In order to compare with the new composite coating, the traditional 321 coating with twin 321 stainless steel wires was fabricated. The microstructure and wear resistance of the coatings were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersion spectroscope (EDS) and MM-200 ring-block type sliding wear tester. Results showed that, except for the aluminum phase addition in the 321—Al coating, no other extra phases produce in comparing with the 321 coating. However, due to the additional aluminum, the 321—Al coating performs quite different microstructure characteristics and tribological behavior. The oxygen content and microhardness of the 321—Al coating are lower than that of the 321 coating, but wear losses are pretty much under the oil lubricated sliding condition. The effect of the microstructure on the wear behavior of the 321—Al coating was also discussed, which is mainly relevant to the characteristic of “ductile aluminum and hard stainless steel composite phases inter-depositing”.

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.

An Automatic High Velocity Arc Spraying System

A new automatic high velocity arc spraying system was developed. The system was consisted of five units, i.e. central control unit, operating machine, positioner, touching screen and high velocity arc spraying equipment. The central control unit is controlled by a program, controlling other four units. Spraying parameters could be input and modified on the touching screen during spraying. The moving of spraying gun was carried out by motion arm of the operating machine. The rotational velocity and angle of components to be sprayed was controlled by positioner. The spraying process for a cylinder body of automobile engine with the system was introduced in detail. The auto and manual arc spraying have been used to fabricate coating. The microstructure of the coatings prepared by the two spraying processing was analyzed. The result shows that the auto sprayed coating has a more uniform and compact structure than that of the manual sprayed coating.

Study States on Surface Protection of DS Surface Material Damage

This paper mainly introduced the causations of deep-sea submersible (DS) surface material damage and some methods of research on corrosion and fatigue. It is suggested that investigating the mechanisms and effects of corrosion and fatigue damage on DS steel structure and coating, and the mapping relation for the origin and accumulation of cross scale damage should be established. In addition, organic coating, metallic coating, steel matrix and their interaction could be detected and analysed using the methods of SEM, XRD, TEM, EIS, EN, CV, Kelvin probe and so on. At last, mathematical model of service life for the steel structure and coating should be established for the quantification study

Study on Composition and Mechanical Property of New High Abrasion Resistant Alloy Used in High Arc Spaying

Spraying wire was widely used in remanufacturing work piece for worn failure. With the demand of high abrasion resistant wire, new type alloy was developed. The solidification structures of the new high abrasion resistant alloy (HARA) containing Mn, Cr, Si, C and the structure was studied after tension by scanning electron microscopy (SEM). The phase evolution was analyzed by X-ray diffraction and Rockwell hardness evaluated on the hardness testing. The abrasion behavior of HARA alloy used in the liner of wet-grinding machine in metallurgical industry is investigated under impacted energy of 0.5-3 J in acid-ironstone slurry; the test was carried out by a modified MLD-10 tester. The result show that the solidification structures of HARA alloy consist of austenitic Fe and the hardness neared to HRC60. Under the high energy, the wear resistance of HARA alloy is three times more than Mn13. Therefore, the new material has better abrasive wear resistance and lower environmental impact

Preparation and Hardness Behavior of Al-Based Amorphous/Nanocrystalline Composite Coatings on Mg Alloy Prepared by High Velocity Arc Spraying Process

High velocity arc spraying (HVAS) process was used to deposit Al-Ni-Y-Co and Al-Ni-Mm-Fe amorphous/nanocrystalline composite coatings onto AZ91 Mg alloy substrate. Their microstructure was characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The coatings are both about 500 μm in thickness with fully dense and low porosity. The microstructure of the coatings is classified into two regions, namely, a full amorphous phase region and homogeneous dispersion of fcc-Al and some intermetallic nanoscale particles in a residual amorphous matrix region. Vickers micro hardness of the coatings was also measured. The average Vickers micro hardness of Al-Ni-Y-Co and Al-Ni-Mm-Fe coating is about 311 HV and 340 HV, respectively.

Elastoplastic analysis of process induced residual stresses in thermally sprayed coatings

The residual stresses induced from thermal spraying process have been extensively investigated in previous studies. However, most of such works were focused on the elastic deformation range. In this paper, an elastoplastic model for predicting the residual stresses in thermally sprayed coatings was developed, in which two main contributions were considered, namely the deposition induced stress and that due to differential thermal contraction between the substrate and coating during cooling. The deposition induced stress was analyzed based on the assumption that the coating is formed layer-by-layer, and then a misfit strain is accommodated within the multilayer structure after the addition of each layer (plastic deformation is induced consequently). From a knowledge of specimen dimensions, processing temperatures, and material properties, residual stress distributions within the structure can be determined by implementing the model with a simple computer program. A case study for the plasma sprayed NiCoCrAlY on Inconel 718 system was performed finally. Besides some similar phenomena observed from the present study as compared with previous elastic model reported in literature, the elastoplastic model also provides some interesting features for prediction of the residual stresses.

Corrosion Protection of A3 Steel with Zn-Al-Mg-RE Coating from Arc Spraying

Cored wires and high velocity arc spraying (HVAS) technologies have been applied to produce Zn-Al-Mg-RE coating on A3 steels. The durability of coating in terms of corrosion resistance is the focus of this paper. The detailed degradation mechanism has been investigated using electrochemical-monitoring techniques supported by precise pre-test and post-test microscopical examination using Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). Zn-Al-Mg-RE coating shows a typical aspect of layered heterogeneous structure, the existing of ZnAl2O4 and MgAl2O4 implies the good anti-corrosion feature. The polarization curves showed that Zn-Al-Mg-RE coating exhibits passive behavior at 0.5h and 16h immersion, but at 600h, it begins to dissolute. In contrast, the anti-corrosion performance isn’t cut down. The corrosion potential moves to the noble direction step by step, along with the current density drops gradually. After corrosion, it has been observed that the coating surface is jointed by flaky lamellar products and dense without obvious defects and pores. It is postulated that with the addition of RE, the porosity of the coating is reduced, meanwhile, the stability of the products layer can reinforce the self-sealing effect of the coating distinctively.