Abstract
This article is aimed to discuss the chemical aspects of detonation spraying of powder materials. In this method of coating deposition, ceramic, metallic or composite powders are injected into the barrel of a detonation gun filled with an explosive gaseous mixture. When the latter is ignited, the powders are heated and accelerated toward the substrate. Subjected to high temperatures, the powders are prone to chemical reactions, the reaction products possibly becoming the major phase constituents of the coatings. What types of reactions are possible? Can these reactions be carried out in a controlled manner? We answer these questions considering the interactions of the sprayed powders with the gaseous environment of the barrel as well as those between the phases of a composite feedstock powder. In Computer-Controlled Detonation Spraying (CCDS), the explosive charge and stoichiometry of the fuel-oxygen mixtures are precisely measured and can be flexibly changed. Our studies demonstrate that with the introduction of a highly flexible process of CCDS, detonation spraying has entered a new development stage, at which it can be considered as a powerful method of composition and microstructure tailoring of thermally sprayed coatings. During CCDS of TiO2-containing powders, chemical reduction of titanium dioxide can be carried out to different levels to form either oxygen-deficient TiO2−x or Ti3O5 suboxide. CCDS of Ti3Al can produce titanium oxide coatings when oxidation by the detonation products dominates or titanium nitride-titanium aluminide coatings when oxidation is hindered but the interaction of the powders with nitrogen—a carrier gas component—is favored. During detonation spraying of Ti3SiC2–Cu composites, the Ti3SiC2 phase is preserved only in cold conditions; otherwise, Si de-intercalates from the Ti3SiC2 phase and dissolves in Cu resulting in the formation of the TiCx–Cu(Si) composite coatings.
Keywords
Detonation spraying; Coatings; Oxides; Intermetallics; Metal–ceramic composite
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