Papers by Keyword: Arc Spray

Abstract: Thermal spray coatings have become one of the most potential for hard chrome replacement, particularly for wear and corrosion applications. In this study four types of hard coating materials were selected and thermally sprayed by suitable processes as the following designated codes (material/spray technique): Cr-Fe/HVOF, Cr-Ni/HVOF, WC-Ni/SF and Cr-Fe/AS. All of starting materials were characterized in order to create a correlation between spray materials and coating characteristics. SEM was employed for morphology and microstructure investigation. Particle size analysis was investigated by SEM and laser particle size analyzer. Coating characterization included surface roughness measurment by profilometer, porosity evaluation by image analysis and hardness test by Vicker microhardness tester. Microstructure of coatings was also revealed by SEM. Wear performance was evaluated by pin on disc test and dry sand rubber wheel abrasion test. Corrosion resistance was tested by potentiodynamic method. The results showed that particle size and morphology of starting powders were various depending on manufacturing method. Chemical compositions of starting materials showed great effect on coating properties and performance. Coatings deposited by HVOF and spray & fuse (SF) method showed typically dense and homogeneous structure than arc sprayed coating. WC-Ni/SF coating showed lowest abrasive wear rate compared to other thermally sprayed coatings. All Ni base coatings had significantly lower corrosion rates while Cr-Ni/HVOF coating had lowest corrosion rate. Although Cr-Ni/HVOF and WC-Ni/SF could be applicable for both wear and corrosion applications, for heat sensitive parts, Cr-Ni/HVOF coating could be a better alternative to spray and fuse.

Abstract: nanostructured coating materials become demanding, since it improves the mechanical properties, such as hardness, through grain refinement. One of the methods of producing nanostructured coatings is to use an arc spray coating process using nanostructured wires. Although the arc spraying process is well developed, the influence of nanoparticles on the fracture toughness of the coating surface has not been examined in details. Consequently, in the present study, arc spraying of nanostructured wires on carbon steel surface is carried out. The influence of coating thickness on the microstructure and fracture toughness of the coating is investigated. It is found that the self-annealing due to large coating thicknesses has a noticeable effect on the microstructure and fracture toughness.

Abstract: Aluminum coatings were developed by arc spray on mild carbon steel Q235. Scanning electron microscopy detection shows that the coatings have good bonding with the substrate and have low porosity. The corrosion behaviors of the coatings in splash zone were studied. The results show that free corrosion potentials of aluminum coatings are much lower than that of Q235. Potentiodynamic polarization measurements reveal that the curves of aluminum coatings have activity anodic dissolution zone, passivation zone and super-passivation zone. Corrosion morphology and energy dispersive spectrometers show that Cl^- can penetrate into the coatings and some of the substrate has been corroded. The arc spray Al-coating develops a film of corrosion products on the coating surface, which tend to seal the pores in the coatings. Arc spray aluminum coatings can protect the substrate from corrosion in splash zone.

Abstract: Characteristics of in flight particle and splat fabricated by arc spraying of three different types of cored-wire including WC-Cr-Ni, WC-Cr-Fe and W-Cr-Fe nano-composite were revealed. In-flight particles and splats were deeply characterized in order to correlate their characteristics that forming coating and affecting coating structure and properties. Starting cored-wires were also characterized prior to being sprayed. Particle size, morphology microstructure, chemical composition and phase identification were investigated through various techniques. The results showed that the size of the in-flight particle did not depend mainly on the size of filler particles as expected, but was instead strongly related to the whole content of metallic phase composed the cored-wire, as the more metal composition the larger size of the in-flight obtained. Splat shapes and characteristics were also found to depend on the metal content; a flower shape splat with a high degree of splashing was predominant for cored-wire having more metal composition. The W-Cr-Fe nano-composite cored wire had the highest content of metallic binder phase, which resulted in the largest in-flight particles produced, and well melted of the metallic phase led to the highest degree of splashing observed.

Abstract: Pseuado Zn-Al alloy coatings were made by using of dissimilar metal wire arc spraying technology on the surface of the steel Q235 and the H2S corrosion experiment was carried out on the coatings. The corrosion rate was calculated with weight-loss method. The configurations of Zn-Al coatings before and later suffered corrosion were observed with scanning electron microscope, and the coating surfaces were analyzed with energy spectrum. The corrosion potential of the coatings was tested by using the electrochemistry testing system. The corrosion results showed that Zn-Al coatings can protect the covered steel surface and the steel substrate exposing in the corrosion environment. Being processed with pore sealer, the coatings have shown more excellent corrosion resistance.

Abstract: Functionally graded mold (FGM) is the trend in the development of modern mold. Based on the optimization of electroforming and arc spray forming, a functionally graded mold with the structure of Ni-NiAl-ZnAl-Zn was manufactured, and the microstructure of the mold shell was analyzed. The experiments show that the manufacturing of functionally graded mold by electroforming and arc spray forming is feasible in engineering. The research is of significant value in exploring new manufacturing technology of functionally graded mold.

Abstract: 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”.

Abstract: Correlations between in-flight particle, splat and coating microstructure of thermally sprayed Ni20Cr were investigated. Flame spray and arc spray systems were employed for spraying Ni20Cr powder and Ni20Cr wire, respectively. The results showed that the arc spray process produced a broader size distribution for both in-flight particles and splats compared to flame process. Flower-like splat morphology was obtained from the arc spray whereas a pancake-like splat was obtained by flame spray. Ni20Cr coating sprayed by arc process had a denser microstructure, lower porosity and better adhesion at the interface. This could be due to the higher temperature and velocity from the arc spray process enhancing the melting and adhering for coating formation.

Abstract: Aluminum arc spray process was employed to form an aluminum coating on AZ31 magnesium alloy substrate. Anti-corrosion property of the Al-coated specimens was evaluated by salt immersion tests and electrochemical tests. There was no apparent inter-layer diffusion or compound layer formation between the aluminum coating and the substrate under as-sprayed condition. To improve the density of the coating and the bonding strength between the coating and the substrate, a heat treatment process was conducted after spraying to form an interlayer by metallurgic diffusion. The interlayer consisted of large primary crystal Mg17Al12 phase and minute lamella structure that consisted of Mg17Al12 and α-Mg. The hardness of both the aluminum coating and the interlayer are higher than that of the substrate. In electrochemical experiments, the corrosion current density decreased from 2.4×10-1mA/cm2 of AZ31 to 7.1×10-3mA/cm2 of heat-treated specimen. It suggests that the corrosion resistance of AZ31 can be greatly improved by aluminum arc spray with a following heat treatment process.