Phase Formation during Deposition of TiO₂ Coatings through High Velocity Oxy-Fuel Spraying

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The crystalline structure of TiO₂ coating is of significant importance for controlling its property and performance, such as photocatalytic activity. The aim of this study is to examine the phase formation mechanisms during high velocity oxy-fuel (HVOF) spraying of TiO₂ coating. TiO₂ coatings were deposited under different spray conditions using both anatase powder and rutile powder as feedstocks. The results showed that the anatase content in the coatings was increased with the increase of fuel gas flow when using the rutile powder as feedstock. A TiO₂ coating of anatase content up to 35% can be obtained by well-melted particles. The high content of anatase phase possibly resulted from rapid solidification and cooling process of the particles. The anatase content in the TiO₂ coating deposited with an anatase powder in partially melted state reached 55–65%. The coating deposited by well-melted anatase powder contained the same anatase content as that by rutile powder. A model was proposed to explain the phase formation within the coatings deposited through HVOF spraying.