An experimental design matrix was set up in which carbon steel coatings were deposited with a twin wire arc spray gun (TAFA 9000 TM ), using either compressed air or nitrogen as spraying gas. The coating's mechanical properties were studied. Some correlations were made between these properties, spraying conditions and the microstructure of the deposits. Young's modulus was estimated by the single beam method using finite element modeling. Results show that direct relationships do exist between spray conditions, oxide content in the coating and microhardness. Young's modulus of the coatings depends on the lamella thickness and the oxide content. When increasing the compressed air flow rate, Young's modulus increases at first because smaller particles and finer lamellae were made and it decreases later because of a higher oxide content. The increase of nitrogen flow rate lowers the oxide content and increases Young's modulus. #

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Al2O3-SiCw (SiC whisker) powders were plasma sprayed on carbon steel under the electrostatic field. Effect of voltage on the microstructure and mechanical properties of the coatings was investigated. The erosion resistance was measured on the rotating disk erosion tester. The micro hardness and fracture toughness were obtained by the indentation method. It is found that the phase composition is unchanged for the coatings deposited in the presence or absence of electrostatic field while the grain size of coatings varies with the voltage. The porosity of coatings increases with the voltage slightly at first, and then a decrement tendency can be found. The erosion weight loss shows the similar trends with the porosity under the influence of voltage. The fracture toughness is the lowest when the voltage is 10 kV, and it is the highest for coatings deposited under no electrostatic field. The measurement of hardness yields the similar results though the voltage is different. The deflection behaviour of whiskers under the electrostatic field affects the deposition of molten powder and then the microstructure and properties of plasma sprayed coatings.