Detonation Spraying of TiO2-Ag Powders Under a Controllable Atmosphere

Abstract

Abstract In the present work, TiO2(rutile)-2.5vol.%Ag composite powders produced by mechanical milling were detonation sprayed under different atmospheres using acytelene as a fuel. The atmosphere of spraying was set to be reducing or oxidizing by changing the O2/C2H2 mole ratio. Reduction of TiO2 to Ti3O5 occurred in the coatings deposited under a reducing atmosphere (O2/C2H2 =1.05) when particles were heated to reach a molten or a semi-molten state. In the coatings sprayed using a stoichiometric O2/C2H2 =2.5 mixture, the major phase was rutile. The composition of the atmosphere does not only determine the chemical environment for the sprayed powders, but also influences the temperature conditions. Increasing oxygen content in the explosive mixture led to much higher temperatures of the sprayed particles as was calculated using a previously elaborated model. When titanium dioxide did not reach melting, the coatings were porous with a spongy surface. Coatings formed by fully or partially molten particles possessed a denser structure. Silver particles experienced melting during spraying but remained uniformly distributed in the coatings. This study demonstrated that careful selection of the composition of the spraying atmosphere offers potential of controlling the phase composition and microstructure of the detonation sprayed coatings.