The paper is devoted to gaseous detonation spraying and presents the state of current knowledge, as well as the following research and development needs: gaseous detonation as spraying heat source; operation cycle of detonation guns and its possible versions; operating frequency; impulse jet formation; basic detonation guns design concepts, as fuel and oxidant types, features of barrel design, predetonation distance control, valved and valveless detonation guns concepts, etc.; gas dynamic characteristics of detonation spraying.

Current understanding of mechanisms of splat formation during thermal spraying are discussed. Schematic of influence of particle velocity on change of impact and forward pressure during particle-substrate interaction are given. The existence of three typical zones of particle-substrate contact is shown. These zones are: (1) central circle type mechanically activated by hammer and head pressure; (2) middle ring-shaped mechanically activated by head pressure and friction of spreading particle; (3) peripheral ring-shaped mechanically activated by friction of spreading particle. It is possible to estimate dimensions of these zones analytically. The stress distribution on particle-substrate contact during splat formation is discussed. It is shown that relative values of area for these zones depends from particle velocity. The presence of these typical zones during splat formation shown by conduction of special model experiments.

The influence of the particle velocity on the formation intermetallic of coatings is discussed. The primary phases of detonation sprayed NiAl coatings are NiAl and Ni 3 Al, and also a solid solution of Ni in NiAl. The lamellar and homogeneous distribution of Al may be due to the oxidation of the powder particles during their flight in the pulsating high temperature, high velocity jet of the gas detonation process. During heating and melting of the powder particles, an aluminum oxide film is formed. This film takes part in the coating formation and affects the Al distribution. Another important observation is the presence of NiAl and Ni3Al phases in the coating structure. The transition zone between the coating and substrate has a thickness of 10-15 µm. The character of the distribution curves of Al and Ni confirms the lamellar distribution of NiAl and Ni 3 Al phases in the coating.

The mathematical model intended for modeling of the acceleration, heating, and melting of alloyed cast iron particles into plasma jet is presented. Comparison of mathematical modelling and experimental measurement results showed fairly good agreement.

The principles of system approach to modeling of sprayed particles interaction with substrate in process of thermal spraying of coatings are discussed. The proposed model have six levels for analysis of particle-substrate interaction system: functional, technological, mechanical interaction, thermal, mass transfer level, and metallophysics level.

Manufacturing of alloyed cast iron forming rolls is accompanied by generation of valuable solid waste as cutting and grinding swarf. The objective of this investigation was to evaluate the potential for mill debris to be used as a new source of inexpensive powders for thermal spraying of wear resistant coatings. More than 25 high-carbon iron alloy compositions are used in roll production. The structure of these cast irons usually includes from 2 to 4 phases (such as troostite, bainite, needled martensite, austenite, and graphite). The properties of powders obtained from mill debris were characterized in terms of particle size and shape, composition, structure, technological fluidity, and bulk density. The obtained powders were used for plasma spraying of wear resistant coatings. The results indicate that cutting and grinding swarf may be a feasible raw material source for economical alloyed powders, granules, and other materials for coatings. The composite plasma sprayed coatings obtained from powder mixtures of alloyed cast iron and nickel-base alloy have better tribological performance in comparison to coatings from any single powder alloy.

This paper examines plasma-sprayed layers obtained from low-cost mixtures of cast iron and NiCrSiB powders. The composite coatings are characterized based on friction and wear testing and are found to have better tribological properties than coatings produced from any single alloy powder. The structure and properties of composite layers with different compositions of iron and nickel are investigated as well. Paper includes a German-language abstract.