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Dina V. Dudina, Sergey B. Zlobin, Natalia V. Bulina, Alexey L. Bychkov, Vladimir N. Korolyuk, Vladimir Yu. Ulianitsky, Oleg I. Lomovsky
Journal of the European Ceramic Society Volume 32, Issue 4, April 2012, Pages 815–821
Abstract
In the present work, rutile powders containing additions of metallic silver (2.5 vol.%) were detonation sprayed in a reducing atmosphere formed by gaseous detonation products of the C2H2 + 1.05O2 mixture. The initial volume of the C2H2 + 1.05O2 mixture – explosive charge – used for a detonation pulse was computer-controlled as the fraction of the barrel volume filled with the mixture. Using a previously developed model of the detonation process, the particle temperatures and velocities were calculated to explain the observed phase and microstructure development in the coatings. With increasing explosive charge, the temperature of the sprayed particles increased and rutile was partially reduced to oxygen-deficient TiO2−x and then to Ti3O5. When the melting temperature of rutile was not reached, the coatings were porous; semi-molten particles formed denser coatings obtained with higher spraying efficiency. Silver inclusions in the titanium oxide matrix experienced melting and substantial overheating, but remained well preserved in the coatings.
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Additional Information
Coatings were fabricated with the help of a new generation detonation gun – Computer Controlled Detonation System CCDS2000 (see a gun unit in fig.1.), which was developed in Lavrentyev Institute of Hydrodynamics (LIH SB RAS). CCDS2000 has the following important advantages:
– the operating unit with two attached powder feeders is a mobile module weighing less than 20 kg and compatible with a conventional industrial robot;
– the powder feeder provides the radial supply of a precise quantity of the powder in a narrow zone of the barrel, which is better than the axial supply in terms of coating quality and reduction of powder losses (the powder efficiency reaches 70-80% in these feeding systems);
– a possibility of operation at 10 Hz allows increasing the powder deposition rate up to 5 kg/h;
– when acetylene is used as a fuel, the temperature of the detonation products reaches 4500 K (700-800 K higher than in the HVOF process), which makes it possible to deposit high-melting point materials such as molybdenum;
– a gas-supplying system with a four-line gas-distributor based on fast-response electromagnetic valves and a unit of stabilizers provide high-precision and an absolutely stable supply of working gases; spraying modes with two fuels (e.g., acetylene and propylene) are also possible;
– the computer control guarantees a stable spraying process and a stable coating quality without any intervention from the operator during the spraying process;
– an autonomous air-radiator cooling system provides strict thermal stabilization of the detonation gun;
– a specialized 3-D manipulator with stepping motor drivers is an option enabling scanning of the substrate surface in coordination with the gun shooting;
– high-precision movement drives make it possible to implement a number of processing techniques for parts of irregular shape providing a uniform coating thickness on 3-dimensional surfaces.
The temperature, velocity of the sprayed particles and the chemistry of the spraying environment can be controlled by varying the fuel to oxidizer ratio and the amount of an explosive mixture used for the shots of the detonation gun. This creates multiple opportunities to tailor the chemical and phase composition of the coatings as well as their microstructure. Chemical reactions of reduction or oxidation take place in the sprayed material in a controlled manner, based on which coatings of unique structure and properties can be designed [D.V.Dudina et al. Intermetallics 29 (2012) 140; D.V.Dudina et al. Ceram. Trans. 237 (2012)161].
Contacts:
Prof. Vladimir Yu. Ulyanitskiy
Head of Detonation Flow Laboratory
Lavrentyev Institute of Hydrodynamics SB RAS.
Tel: (383) 333-00-03; Fax: (383) 330-48-51; E-mail: [email protected]
