Preparation And Properties Of SiCw-reinforced Alumina Coating Deposited Under The Electrostatic Field

In order to improve the performance and service life of industrial equipment applied in erosion circumstance, erosion-resistant ceramic coating has been widely used in many industrial fields. However, the inherent lamellar structure of ceramic coating fabricated by APS determines its low lamellar bongding ratio, limiting the properties and application of ceramic coating. SiCw is broadly adopted as the second reinforcement in ceramic matrixs for its excellent mechanical, physical and chemical properties. In terms of substantial non-bonded lamellar interfaces existing in ceramic coating, Al2O3/SiCw composite coatings are prepared by APS in this study. Based on whisker reinforcing mechanisms, electrostatic field is exerted in the spraying process to make whiskers arrange at a certain direction vertical to coating surface. The microstructure and phase composition of the coatings prepared under different electrostatic voltage are analyzed via SEM, EDS and XRD. By measuring the microhardness, fracture toughness and erosion resistance of the coatings, the mechanism is studied about the infuence of whisker orientation on the properties of the composite coating.It is concluded that spray granulation with sintering is an effective way to prepare Al2O3/SiCw feed powder. After plasma spraying, the unmelted SiCw are found bridging the lamella or embedding in Al2O3 splats. The porosity of coatings increases with the voltage slightly at first, and then a decrement tendency can be found. ?-Al2O3 in powder converts to metastable ?-Al2O3 in coating, with both fractional stable ?-Al2O3. SiCw retains in p-SiC phase after plasma spraying. The phase composition is unchanged for the coatings deposited in the presence or absence of electrostatic field. However, the grain size and residual stress of coatings varies with the voltage. The measurement of hardness yields the similar results though the voltage is different. The fracture toughness is the lowest when the voltage is 10 kV, and it is the highest for coating deposited under no electrostatic field.The erosion weight loss shows the similar trends with the porosity under the influence of voltage. The mechanical properties of coating including erosion resistance and fracture toughness are affected by the coating porosity. The mechanism of this variation is that the deflection behaviour of whiskers under the electrostatic field affects the deposition of molten powder. The hindrance effect on the deposition of droplets varies with the SiCw average orientation angle, which further results in different bonding condition between lamella and then the microstructure and properties of plasma sprayed coatings.