| In this paper,compressed air was used as the plasma gas for the atmospheric plasma spraying to replace the conventional argon-hydrogen plasma gas.The corresponding coatings were prepared by spraying the nano-agglomerated alumina powder and the conventional micron alumina powder respectively.The effects of gas flow rate and arc current on the air plasma jet and the microstructure,phase structure and properties of conventional and nano-structured alumina coatings were studied.The relative contents of ?-Al2O3 and ?-Al2O3 in the conventional and nano-agglomerated alumina coatings were quantitatively calculated by means of X-ray diffraction quantitative analysis.The melting degree of powders was determined under different gas flow rates and working arc currents.The statistical hardness distribution of coatings was analyzed by Weibull function.The wear resistance and bending resistance of the coatings were studied by high-speed reciprocating friction and bending tests.The thermal shock resistance of the coatings was tested by air-cooling method.The results show that the phase structure of the coatings is made up of ?-Al2O3 and ?-Al2O3 by using the nano-sized and micron-sized alumina coating sprayed by the air plasma spray gun.With the increase of the arc current,the melting degree of both powder is increased,and the melting degree of the powder is reduced with the increase of the gas flow rate.The Weibull distribution of nano-structured coatings presents binary structure distribution,indicating that the microstructure of the coatings is composed of partial melting zone and full melting zone.while the micro-alumina coating is composed of completely melted regions and presents a single linear structural distribution.The nano-alumina coating has poor wear resistance,but has high toughness,bending resistance and thermal shock resistance. |
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