Combined damage of cavitation and abrasion is one of the serious problems that affect lifetime and performance on hydraulic machineries and its components. Thermal spraying as a surface hardening and protection technology is required to protect hydraulic components, such as water turbine and radial flow pump, in general. Detonation sprayed coating with high abrasion resistance is one of the promising solutions as the protective coating against combined damage of cavitation and abrasion under solid-liquid double phase liquid conditions. In this study, NiCr-Cr 3 C 2 and WC12Co coatings on the No.45 steel substrate surface have been formed by detonation spraying with the same technological parameter and their properties such as microstructure and microhardness have been studied. The cavitation and abrasion behavior of coatings and the substrate has been investigated using a self-manufactured rotating disk system. The resistance properties of cavitation erosion and abrasion have been illustrated and analyzed with the substrate by the cumulative mass loss curves. The results indicate that, the resistance properties of cavitation erosion and abrasion of NiCr-Cr 3 C 2 coating are the best.

Fe-Al based composite coatings were deposited on Grade 20 steel substrates by High Velocity Arc Spraying (HVAS) technology. Hot salt corrosion properties of the coatings were studied at the temperatures of 450 °C,650 °C and 800 °C . Results showed that the corrosion resistance of the Fe- Al/Cr 3 C 2 composite coatings changed little with the increase of temperature, contrasted to the substrate and Fe-Al coatings. The excellent corrosion resistance of the Fe-Al/Cr 3 C 2 composite coatings was attributed to the oxidation of the iron, aluminum and chromium to form protective scales. In hot salt, there are mainly iron oxides at the outer corrosion surface; aluminum and chromium oxides are found at the inner corrosion surface, which can effectively protect the Fe- Al/Cr 3 C 2 composite coatings from corrosion.

A high efficiency supersonic plasma spray system (HEPJet) was successfully developed with a maximum power of 80 kW and a maximum working gas flow of 6 m 3 /h. It can be used to spray metallic, carbide and oxide powders. The supersonic plasma spraying gun has a single-anode, internal feeding structure. The development of 80 kW inverse power supply with 20 kHz PWM IGBT circuit solved the problems of high output voltage, high output current and strong interference of high frequency. The production cost of this system is only equivalent to that of ordinary plasma systems. The average velocity of Al 2 O 3 particles in the plasma jet measured with a Oseir Spray Watch system reached 740m/s, and the coatings show high quality, good bonding strength and low porosity. The Co/WC coatings deposited by HEP Jet avoided the degradation from WC to W2C which should be attributed to the strong adjustability of the system for jet temperature and jet velocity.

In this study, cored wires and high velocity arc spraying technique (HVAS) were applied to produce Zn-Al and Zn-Al-Mg alloy coatings on low carbon steel substrates. The microstructures and mechanical properties were studied by SEM, EDS, XRD, and Vickers micro-indentor. The electrochemical corrosion behaviors of Zn-Al and Zn- Al-Mg coatings were investigated comparing with Zn and Al coatings in 5%NaCl. The results show that, Zn-Al and Zn-Al-Mg coatings have good quality of uniform microstructure and low porosity. The corrosion resistance of Al coating deteriorated rapidly after nearly 16h immersion, and then kept at a relative stable value. In the contrast, the corrosion potential of the coatings containing Zn decreased a little and then increased towards the noble potential. The potentiodynamic polarization tests show that the icorr value of Zn-Al coating changed greatly at different steps, and it trended to increase continuously which may imply that the coating is easy to be corroded. Comparatively, no obvious change had been found in the Zn-Al-Mg coating which may indicate that the corrosion resistance enhanced with the addition of Mg, and the role of Mg appears to be associated with the self sealing process. Abstract only; no full-text paper available.

Continuously graded yttria stabilized ZrO 2 (YSZ) /NiCoCrAlY coatings were prepared using a high efficiency supersonic plasma-spray system and the thermal shock properties of the coatings were studied. The specimens were so prepared that the two kinds of powders with different melting point were fed to the different regions of the plasma jet by using two powder feeders. The two powders melted perfectly at the same power, and the overheating of the powder with lower melting point was avoided. In this way, a continuously graded transition layer was obtained. The Results show that the continuous change of the coefficients of thermal expansion and thermal conductivity in the transition layer leads to a excellent thermal shock resistance of the totally 0.9mm thick TBCs. The thermal shock cycles of the specimens which underwent heating by oxygen-acetylene flam to 1200 and then quenching into water reached more than 200. The coatings’ surface was still perfect without any visible cracks after the thermal shock test. The analysis shows that the dense structure and the sufficient plastic deformation of the particles depressed the formation of TGOs, which, together with the continuously graded thermal expansion coefficient and thermal conduction coefficient, contributes to the long thermal shock resistance of the coatings.

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.

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.