This study employs a combination of numerical analysis and experimental testing to obtain a better understanding of the changes that occur in hollow spherical metal-oxide powders during detonation spraying and how they affect coating quality. The heating and melting characteristics of hollow spheres are initially calculated for the general case then refined based on a simple detonation spraying model. The estimates are compared with experimental results obtained from detonation-sprayed Al 2 O 3 coatings produced using fused and crushed, dense spherical, and hollow spherical powders. The coatings as well as the powders are characterized based on morphology, particle size distribution, splat formation, cross-sectional microstructure, porosity, and hardness. Important findings, observations, and correlations are identified and discussed in the paper.

This work shows that with computer-controlled detonation spraying, the phase composition of coatings can be changed relative to that of the feedstock powders. New phases can appear in substantial quantities due to chemical reactions of reduction, oxidation, and nitridation as well as interfacial interactions between phases in composite powders. The key advantage of computer control is that it precisely regulates the quantity and stoichiometry of explosive gas mixtures. It has thereby been found that TiO 2 experiences partial reduction to titanium suboxides and that chemical reactions with nitrogen are also possible. It has also been found that when nitrogen is present, titanium aluminides, Ti 3 Al and TiAl, are likely to form nitrides in the sprayed coatings. Interfacial reactions between the phases of a composite have been studied, and in the case of the Ti 3 SiC 2 -Cu system, it has been found that deintercalation of Si can be prevented by maintaining relatively cold spraying conditions. At higher temperatures, coatings of an unusual phase composition form in which carbon-deficient TiCx inclusions are distributed in the Cu matrix as modified by the dissolution of silicon. The formation of new phases affects coating microstructure development and results in new microstructural features.

Characterization of coatings made with the help of Computer Controlled Detonation Spraying (CCDS) was performed. The applied coatings include hard alloys (WC/Co -75/25, WC/Co - 88/12, WC/Co/Cr - 86/10/4, and Cr 2 C 3 / NiCr), aluminum oxide, nickel-chromium self-fluxing alloy, titanium, bronze, and stainless steel. Tribological investigations of coatings were provided using abrasion test (ASTM standard G65), erosion test (ASTM standard G76), and hydro-abrasive test. To make hydro-abrasive tests special device and method were elaborated based on the interaction of water jet saturated with corundum particles with a coating surface.