Due to high melting temperatures and excellent corrosion resistance of refractory metals, they are used for manufacturing parts working under extreme conditions. The formation of refractory metal coatings by thermal spraying is associated with two major challenges: 1) particles of materials having high melting temperatures should be heated to reach a semi-molten or a molten state; 2) oxidation of the metals should be prevented. In this work, the CCDS2000 detonation spray system was used for obtaining molybdenum and tantalum coatings. The coatings were deposited on steel substrates at O 2 /C 2 H 2 =1.1 and stand-off distances of 20 mm and 100 mm. The calculation of the particle temperatures and velocities were carried out to find the optimal spraying modes for Mo and Ta powders. No oxide phases were found in the coatings obtained by spraying of the Mo powder. In the Ta-based coatings, Ta 2 O 5 was found as a second phase. The hardness of the Mo coatings sprayed at 20 mm and 100 mm was 500 HV 300 and 625 HV 300 , respectively. The porosity of the Mo coatings was less than 0.5% for both stand-off distances. The hardness of the Ta-based coatings sprayed at 20 mm and 100 mm was 800 HV 300 and 1000 HV 300 , respectively. The porosity of these coatings was less than 1% for both stand-off distances. The bond strength of the Mo coatings determined by the pin test method was 92 and 126 MPa and that of the Ta-based coatings was 43 and 77 MPa, for coatings deposited at 20 and 100 mm, respectively.

Alumina and chromia coatings were deposited on steel substrates by detonation spraying in order to determine the effect of spray parameters on adhesion, hardness, porosity, and dielectric strength. Test results show that both coatings have low porosity, high hardness, and good adhesion strength and that both can be effective as wear-resistant electrically insulating layers on metal parts.

This study shows that the quality of detonation sprayed coatings can be improved by adding propane or butane to the high-energy acetylene fuel. WC-Co coatings sprayed with binary fuel were found to have very low porosity (< 0.5%), low abrasion wear rates (< 1 mm 3 /1000 rev), high hardness (~1500Hv300g), and good bonding strength (150 MPa). These values were achieved over a range of stand-off distances (150-350 mm) and at a substrate inclination of up to 30°.

Measurement of the particle temperature and velocity in detonation spraying is significantly complicated by the pulsed character of the process. In the present study, these parameters are measured for powders with strongly different nature and properties such as WC/Co, Inox and Ti. Experiments are performed using an original computer-controlled detonation spraying (CCDS) installation developed by the authors. The system is distinguished by the mode of powder feeding into the gun barrel which is pulsed in time and localized in space. Evolution of the particle-in-flight velocity and size is examined by an original CCD-camera-based diagnostic tool developed by the authors. A significant spatial separation of the particles along the detonation plume is observed during their acceleration: 15 μm fine particles overtake 45 μm coarse particles by more than 10 plume diameters. For this reason, distributed scanning over the plume length is applied in order to obtain adequate results. A previously developed mathematical model of the process is experimentally validated. Calculations are found to be in a qualitative agreement with the experimental results. As far as particle-in-flight velocity is concerned, the agreement is even quantitative.

Cold and detonation spraying methods are based on the interaction of high-velocity particles with substrate. High quality coatings from various powder materials can be deposited. In both processes, the substrate experiences insignificant thermal effect. Thermally sensitive powder can be sprayed with no oxidation and decomposition. The initial powder microstructure and even nanostructure can be preserved under properly selected spraying conditions. This study is based on a comparative analysis of the mechanical, electrical, and heat transfer properties of a series of coatings deposited by cold and detonation spraying technologies. The coatings are produced from copper and aluminum powders using a commercial Cold Spray equipment CGT-4000 and an original computer-controlled detonation spraying (CCDS) installation developed by the authors. The coating microhardness, density, electrical and heat conductivity, adhesion, cohesion, etc. are measured and compared. Particular advantages and drawbacks of both spraying methods are discussed.

This study investigates the influence of spraying distance and substrate orientation on the formation of metallic coatings by detonation spraying. Deposition efficiency was determined for aluminum, copper, titanium, and steel powders sprayed at different distances on substrates oriented at different angles. The results show that detonation products maintain their influence on sprayed particles even outside the barrel despite the pulsed nature of the detonation spraying process. Numerical calculations of particle acceleration and heating inside the barrel are performed for several materials and a theory of the processes outside the barrel is proposed. Optimal spraying parameters allowing 60-80% deposition efficiency are defined and experimentally validated for the materials studied.

Properties of detonation coatings from composite powders based on carbides are studied. The main focus is on tungsten carbide. Powders with carbide inclusions of different size ranging from a ten of microns down to the submicron level are analysed. Composites with cobalt binder content from 12 to 30 % and composite binders with chromium and nickel additions are studied. A comparative analysis between composites with chrome carbide and the complex titan-chrome carbide produced by self-propagating high–temperature synthesis is done. Powders are sprayed with a new generation detonation gun “Dragon” designed at Lavrentyev Institute of Hydrodynamics SB RAS. The apparatus is characterized by a high-precision gas supply system and a dosed localized powder feeding system. Computer control provides a flexible programmed readjustment of the detonation gases energy impact on powder particles thus allowing selecting the optimal for each material spraying parameters to form high-quality cermet composite coatings. Physical properties and functional performance of the obtained coatings are studied. Microstructure and microhardness analyses, adhesion/cohesion, abrasion, erosion and friction wear tests of the coatings are performed. It is found that the studied materials do not exhibit overwhelming advantages in performance compared with one another. Fore example, though composites with a great content of binder has a relatively low wear resistance, they exhibits the highest adhesion to the substrate while composites with titan-chrome carbide compared to tungsten carbide-based composites have higher dry friction and lower lubricated friction.

Metallization of plastics by thermal spraying is studied. The possibility to obtain high adhesion of metal particles to the surface of a wide range of plastic materials is shown. Powders are sprayed with a new generation detonation gun “Dragon” designed at Lavrentyev Institute of Hydrodynamics SB RAS. The apparatus is characterized by a high-precision gas supply system and a dosed localized powder feeding system. Computer control provides a flexible programmed readjustment of the detonation gases energy impact on powder particles which is a key factor in precision control of spraying parameters for low-melting point powder materials. It is found that under certain spraying conditions molten particles of a low-melting point material not only do not provoke erosion of plastic material at their high velocity impact on the substrate but strong-bond fusion, sufficient to further form a thick coating, occurs. Aluminium, zinc and tin powders are sprayed on substrates from fibreglass, polyester, fluoroplastic and some other plastics. Load capacity of the obtained coatings reaches 100 kg/cm 2 . It is shown that on top of a thin layer from a low-melting point powder material high-melting point metals and even ceramics can be deposited.