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°.

A new approach has been developed for monitoring thermal spray processing that involves visualization of the movement of particles using a high speed video camera and wide-band intensive illumination to measure particle temperature, velocity, size, and distribution. Synchronously with the capture of the particle parameters, the surface temperature of the coating is measured with a two-channel pyrometer that has high spatial and a temporal resolution. This paper presents the results of investigations of cold spraying and D-gun spraying using these techniques.

The cold gas dynamic spray process offers a unique advantage to form composite coatings by applying powder mixtures. The powder mixture constituents are supposed to interact with each other during impact. In this study, Al and Cu-based powder mixtures are used with the aim to define specific features of the coating formation. Composite coatings with different Al 2 O 3 , SiC, and Ti content are sprayed. Impact behavior of various powder mixtures is analyzed based on scanning electron microscopy images. The Al 2 O 3 and SiC phases of the initial powder are found to be fractured on impact and preserved in the coatings. Another advantage of the kinetic spray process is the ability to mix materials which would normally react with each other and form a composite coating. Some experimental data of such reactions are discussed. Within the composite coating, each constituent changes the initial properties of the sprayed powder material: for example, the soft matrix is strengthened, and hard particles are fractured. The fracture and deformation behavior of the particles and their reactions induced by the impact are determined by micromechanical tests and EDX analysis. Morphology, physical and mechanical properties of the sprayed coatings are discussed.

Deposition of Metal Matrix Composites (MMC) has been the subject of extensive research in the recent years. The desired functional properties of a composite coating can be achieved by analyzing and controlling the major structural processes taking place during deposition. The latter are reactions at the particle-particle and particle-substrate interfaces which can be controlled by applying advanced spraying technologies. Cold Spray (CS) and Computer Controlled Detonation Spraying (CCDS) are well-proven reliable methods for deposition of composite coating. The energy (thermal and kinetic) imparted to the particles-in-flight by CS and CCDS allows initiating interface reactions that will define distinct properties of the deposited composite layers. The applied spraying technologies are characterized by different ratio of thermal-to-kinetic energy that results in different conditions of the compounds interaction. The objective of the present study is to define the effect of CS and CCDS technologies on structure and properties of Al-Ti-based composite coatings by analyzing intermetallic reactions occurring during the process. It is shown that both CS and CCDS composites present differently sized zones of interfacial reactions.

A new approach has been made in monitoring of the thermal spraying. Monitoring of the process is based on visualization of particles movement using both high speed video camera and wide-band high intensive illumination and measurements of particles temperature velocity and size and their distribution. Synchronously with the registration of the particles parameters surface temperature of the coating has been measured with 2-channel pyrometer with a high spatial and a temporal resolution. The results of investigations of the Cold spraying and D-gun spraying are presented.

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.

Spraying metal-ceramic coatings is a complicated task because, in addition to the spray parameters of the metal particles, it is necessary to take into account those of ceramics. This paper presents some results concerning the effect of the nature, particle size, and velocity of ceramics on the metal-ceramic coating properties. Copper and aluminium powders are used as metal components. Two fractions (fine and coarse) of aluminium oxide and silicon carbide are sprayed in the tests. Ceramic particle velocity is varied by the particle injection into different zones of the gas flow: in the subsonic (pre-chamber) and supersonic parts of the nozzle, and in the free jet after the nozzle exit. Simulation results and measurements of the particle velocity by the track method are compared. Influence of the ceramic particle parameters on the coating formation process and its properties is discussed.

Particle-at-impact parameters in Cold Spray are governed mostly by gas flow parameters. However, the location of the powder injection can be used as independent factor to modify particle-in-flight parameters. Calculations and experiments confirm strong influence of the location of the powder injection on dynamics of particle acceleration and heating. Application of this effect for cold spraying of multicomponent coatings is a new and promising approach. The general scheme of spraying of two-component mixture composed of hard-sprayable and easy-sprayable components proposed as follows: The hard-sprayable component is injected into the subsonic part of the nozzle at a gas stagnation temperature favorable for this material to start the coating formation alone. The zone of injection of the easy-sprayable component is determined in such a way that the particles of this material have, at the nozzle outlet, values of temperature and velocity sufficient for the coating formation at the selected gas stagnation temperature. New design of spraying nozzle for the above purposes is proposed and discussed.

The aim of this study is to analyze the shape of splats deposited by detonation spraying and correlate splat morphology with the velocity and temperature of particles as they hit the substrate. The obtained results are in good agreement with numerical calculations for nickel splats and show that the thermo-physical properties of composite particles can be estimated from their splat characteristics as well. An understanding of these relationships for various materials is necessary to calculate particle heating in the detonation barrel.

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.

This paper presents some results of investigation of the cold spraying various composites including metal-ceramics, metal-metal with a new nozzle design. The objective of this study was to develop a nozzle with an ejector that allows the injection of powder components in different points of the gas flow that can provide optimal spray parameters for each component. For this purpose the installation was equipped with three feeders and three powder feed ports. The first one was located in a pre-chamber (high pressure powder feeder) and two others were located in the ejector in supersonic part of the nozzle. Varying the powder injection location of any component allowed us to change the spray parameters of the mixture. Some preliminary spray results of different powder mixtures are presented to illustrate possibilities of such approach. It is shown that an addition of ceramic or metal powder to the sprayed metal can significantly change the spray process and coating characteristics

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.

Laser assisted direct metal deposition (or simply DMD) belongs to the family of laser cladding. This is flexible and efficient method for elaboration of diverse coatings including functionally graded, multi-layered, etc. The coatings are characterized by excellent adhesion (metallurgical contact), low porosity and variable thickness up to several millimeters and even centimeters. Actually DMD technology is under intensive development. The most important objective is to increase product quality, process stability and reproducibility along with the simultaneous decrease of risks, failures and defects both on processes and on end-products. The use of the TRUMPF 505 DMD machine with 5 kW CO 2 laser allowed to scale-up the technology to an industrial level. The targeted applications are related to petrol, chemical and plastics industries where wear resistance is improved by deposition of a hard-phase coating; in aeronautics DMD is used for near net shape manufacturing from Inconel alloys.

The aim of this paper is to develop a model that describes the heating of porous aluminum oxide particles in the plasma jet of the APS process. The model is then used to analyze sintering effects and thermal gradients in particles of varying porosity in-flight. Paper includes a German-language abstract.

This work evaluates the capabilities of a digital camera selected for use in a thermal spray diagnostic system. The CCD-based image sensor, a Sony Exview HAD, was tested in an industrial plasma-spraying process and is assessed in terms of the information it provides about the plasma jet, particle-substrate interactions, and coating growth. Zirconium dioxide and aluminum oxide ceramics are examined as typical powder systems. Paper includes a German-language abstract.

This paper compares two approaches for monitoring in-flight particle properties during thermal spraying, one based on an industrial CCD camera, the other on a commercial diagnostic system. The camera and detector of the diagnostic tool were installed on opposite sides of a jet axis at a point where a workpiece would normally be placed for coating. Test results for a wide range of powder mixtures sprayed using different plasma and HVOF guns show good agreement between the two approaches in terms of the absolute values measured and the basic tendencies of variations in spraying parameters. A statistical evaluation of particle size, speed, and temperature is also carried out in order to determine the influence of process parameters on powder jet characteristics. Paper includes a German-language abstract.