Cored wires and high velocity arc spraying technique (HVAS) were used to produce high Mg content Zn-Al-Mg alloy coatings on low carbon steel substrates. The microstructures, mechanical properties and electrochemical corrosion behaviors of the Zn-Al-Mg coatings were investigated comparing with Zn and Zn-Al alloy coatings. And the electrochemical corrosion mechanisms of the coatings were discussed. The coatings show a typical aspect of layered thermal sprayed material structure. Chemical analysis of the coating indicated the composition to be Zn-14.9Al-5.9Mg-3.0O (wt.%). The main phases in the coatings are Zn, Mg 2 Zn 11 , Al 12 Mg 17 and MgAl 2 O 4 , together with a little Al 2 O 3 and ZnO. The Zn-Al-Mg coatings show higher electrochemical corrosion resistance in salt solution than Zn-Al coatings. The corrosion potential of Zn-Al and Zn-Al-Mg coatings decreased a little and then increased towards the noble potential. The analysis of XRD and Electrochemical impedance spectroscopy (EIS) shows that, with addition of Mg, the corrosion products can block off the pores in the Zn-Al-Mg coating, which is so-called self sealing, and thus prevent attack on the underlying steel substrate.

Nanostructured and conventional WC/Co coatings were prepared by supersonic plasma spraying process respectively. The bonding strength, microhardness, tribological characteristics such as friction coefficient and wear resistance, microstructure and the phase ingredient were studied. The result of the XRD suggests that the coating contains low-carbon phase. TEM analysis reveals that WC phase with the dimension of about 100nm is dispersed in the nanostructured coating. Results of mechanical and tribological properties tests show that nanostructured coating has better performance in comparison with conventional one, with increase of about 40% in the bonding strength, 3% in the microhardness, 14% in the wear resistance, and a decrease of 0.06 in friction coefficient, respectively. After tribological properties tests, obvious plastic deformation was observed on the wear trace surface of the nanostructured coating, while microcrack existed on the surface of conventional coating. Superfine grain strengthening is the primary reason that enhances the performances of the coating.

The delamination wear mechanism of the thermally sprayed coatings was studied by analyzing coatings structural feature and stress distribution on the warm surface, and the influencing factors on the delamination wear were discussed. And the delamination wear mode of coating was developed. The results show that, the thermally sprayed coatings have typical aspect of lamellar structure. There are oxide layers between splats, and there also exist porosity and micro-crack in the coatings. The coating surface was subjected to alternately tensile stress and compression stress caused by normal load and friction force during sliding. In a certain depth below the surface, there exists maximum shear stress. Therefore fatigue damage will take place at subsurface of the coating under alternate stress. The adhesion strength between splats of coating prepared by HVAS is by far lower than casting material because of lamellar structure. And the adhesion strength between splats is further weakened due to the defects (such as porosity and micro-crack) appearing mostly on the boundaries between thin oxide sheets and splats. When the fatigue damage accumulates to a certain value, micro-cracks initiate at the defects between splats. Then these micro-cracks grow, connect, and propagate along the defects between splats. Finally, these cracks shear to the coating surface leading to spallation of the splats, and thus wear debris is generated. By repeating the above process delamination of the coatings will occur. Reducing friction coefficient, increasing coatings hardness and adhesion strength between inter-splats are the basic methods to improve the wear resistance of thermally sprayed coatings. Abstract only; no full-text paper available.

Dual-wire arc sprayed Al/Al2O3 MMC coatings have been successfully applied to shipboard and other steel structures. However, the feed wire used is difficult to produce, restricting the application potential of the method. To avoid this difficulty, arc sprayable cored wire was developed, with Al2O3 powder as the filling material and commercial aluminum strip as the retaining sheath. Arc sprayed coatings made from cored Al/Al2O3 wire have been characterized based on bond strength, Al2O3 content, microstructure, microhardness, and wear resistance, and the results are compared with those of pure aluminium coatings.

For the purpose of getting high hardness and high wear-resistant coating by arc spraying technology, the arc spraying of 7Cr13 cored wire is adopted in this paper. The metallurgical process of the cored wire arc spraying is discussed. The bond strength, hardness and tribological properties of the composite coating are investigated.

This paper describes some of the problems solved in the development of a mold-making process in which the molds are coated using a 2mm wire arc-spraying system. A water solution release agent has been chosen to meet industry standards and requirements. The composition of backup materials was chosen based on compression strength testing. The material selected has high ultimate compression strength and high thermal conductivity and can be readily incorporated in the mold-making process.