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Metal matrix composites containing nanoscale carbon (nanotubes, graphene, etc.) are of great interest from the viewpoint of developing materials with improved mechanical properties. In the present work, detonation spraying experiments were conducted to produce composite coatings containing in situ generated nanoscale carbon. The coatings were prepared by detonation spraying with the use of fuel-rich acetylene-oxygen mixtures. When C2H2 + kO2 mixtures with k < 1 detonate, together with gaseous detonation products, solid graphene-like carbon nanoparticles form in the detonation gun barrel. When spraying a powder, these particles enter the coating layer and affect its properties. The phase composition and mechanical properties of coatings obtained from Al, Cu, Ni and Ti powders in the mode of in situ carbon generation are reported. The microhardness of the carbon-containing composite coatings was higher than that of the pure metal coatings and bulk commercial metals. The cohesion of Al- and Cu-based coatings containing carbon and carbon-free coatings did not actually differ. However, the presence of carbon reduced the cohesion of the Ni-based coating by about 30% and, conversely, increased the cohesion of the Ti-based coating by 30%. This work opens a new avenue for research and applications in the area of coatings formed by detonation spraying.

In the present work, Fe66Cr10Nb5B19 metallic glass coatings deposited by detonation spraying (DS) on carbon steel substrates were structurally characterized and tested in 3.5 wt.% NaCl solutions with pH values of 3.0, 5.5, and 10.0 under potentiodynamic polarization conditions. The coatings had low porosity (2.9-4.5%) and showed a predominantly amorphous structure. The concentration of an amorphous phase in the detonation coatings was 97.5-99.5 wt.%. Such high concentrations were not observed in thermally sprayed Fe-Cr-Nb-B coatings obtained by other research groups. Under the test conditions, the coatings exhibited low corrosion current densities (of the order of 10-6 A cm-2) and low passive current densities (below 10-3 A cm-2) while showing extended passive regions (stable within 1.5 V from the corrosion potential). The Fe66Cr10Nb5B19 coatings produced by DS showed a much better corrosion resistance than the carbon steel substrate. Furthermore, the corrosion resistance of the Fe66Cr10Nb5B19 DS coatings was superior to that of flame-sprayed or high-velocity oxygen fuel-sprayed Fe-Cr-Nb-B coatings reported to date. These results open new prospects for the use of affordable and Cr-lean Fe-Cr-Nb-B glassy coatings for carbon steel protection, where chloride-induced corrosion is the major degradation risk, such as metallic components for marine applications.

The feasibility study of elaboration of metal composite coatings by detonation spray using the blends of iron, nickel, copper, cobalt, and aluminum powders was performed using different spray modes. The numerical simulation of particle parameters showed that the particles formed the coating in solid, semi-molten, or molten state depending on the spraying modes, particle material, and particle size. It was shown that successful formation of the coating containing all powder mixture components could be achieved in case of proper optimization of spraying parameters. Obtained Fe-Co-Ni, Fe-Co-Ni-Cu, and Fe-Co-Ni-Cu-Al coatings had the uniform lamellae structure. However, the composition of the coatings differed from the initial powder mixture composition due to different deposition efficiencies of the powders. It was also found the mutual influence of blend components on bonding. In particular, the deposition efficiency of iron particles was probably affected by copper.

This work deals with iron-based amorphous alloys in the form of coatings and sintered materials. It compares the structure and properties of Fe-Cr-Nb-B alloys (Fe66Cr10Nb5B19 and Fe62Cr10Nb12B16) produced by detonation spraying and spark plasma sintering. The Fe66Cr10Nb5B19 alloy has a higher glass-forming ability than Fe62Cr10Nb12B16 and the gas-atomized Fe66Cr10Nb5B19 feedstock powder was mainly amorphous, while the Fe62Cr10Nb12B16 powder with the same particle size range was fully crystalline. Detonation spraying made it possible to produce coatings with an amorphous phase as the main phase with both powders. The microhardness of the Fe66Cr10Nb5B19 coatings was lower than that of the Fe66Cr10Nb5B19 sintered alloy, at the same level of porosity (< 1%). The wear resistance of the Fe66Cr10Nb5B19 coatings was higher than that of the sintered Fe66Cr10Nb5B19 alloy. Fe66Cr10Nb5B19 and Fe62Cr10Nb12B16 coatings showed close values of microhardness and wear resistance under dry linearly reciprocating conditions. Notably, the wear resistance of the coatings was higher than that of stainless steel. This work demonstrated that detonation spraying is suitable for manufacturing amorphous phase-based alloy coatings, even for compositions with moderate glass-forming ability.

In this work, a new two-stage approach to the deposition of high-entropy alloy coatings is proposed. At the first stage, a composite precursor coating is formed by detonation spraying of the metal powder mixtures. At the second stage, the precursor coating is re-melted by a laser, and the formation of multi-component solid solution phases can be expected upon solidification. The feasibility of the proposed approach was validated using three different mixtures of Fe, Ni, Cu, Co and Al powders. It was shown that detonation spraying allows forming composite coatings with a uniform distribution of the lamellae of different metals. The results of the structural analysis of the laser-treated coatings suggest that complete alloying occurred in the melt and face-centered cubic solid solutions formed in the coatings upon cooling.

Coatings deposited by detonation spraying equipment CCDS2000 using alumina powder are studied. CCDS2000 is characterized by a computer control system, robot compatible spraying unit (gun barrel), a portable chiller, two powder feeders, and other peculiar properties. This installation allows to deposit coatings on complex shape surfaces and thin-walled parts under optimal conditions. Studies of the coating properties included measurements of coating microstructure, porosity, microhardness, adhesion, cohesion, abrasive and erosive wear, and dielectric properties (specific resistivity and dielectric strength). The detonation sprayed coatings have an adhesion of 60-70 MPa, cohesion of 100 MPa, microhardness of 1500 HV100, porosity of about 1% (measured on microsections of coatings using OLYMPUS Stream Image Analysis software). Impregnation of coatings with silicone oil showed that the real open porosity of coatings is up to 6%. Dielectric strength of the ceramic layer with the thickness of 200 μm exceeds 30 kV/mm. Specific resistivity depends on atmospheric humidity and when the relative humidity is less than 60%, the specific resistivity is greater than 1013 Ω·cm.

In this work, we traced structural transformations of an Al62.5Cu25Fe12.5 alloy, in which a quasicrystalline icosahedral phase (i-phase) can be formed, upon spraying onto a substrate and consolidation from the powder into the bulk state. The Al62.5Cu25Fe12.5 powder was obtained by gas atomization and consisted of i-phase and ?-phase AlCu(Fe). The powder was detonation sprayed (DS) and consolidated by spark plasma sintering (SPS)/hot pressing (HP). During DS, the particles experienced partial or complete melting and rapid solidification, which resulted in the formation of coatings of a complex structure. The composite regions containing i-phase were inherited from the powder alloy. The fraction of the material that experienced melting solidified as ?-phase AlFe(Cu) in the coating. It was suggested that the difficulty of obtaining i-phase upon post-spray annealing is related to aluminum depletion of the alloy during DS. During SPS and HP, the elemental composition of the alloy was preserved, while the exposure to an elevated temperature led to phase homogenization. SPS and HP conducted at 700?C resulted in full densification and the formation of a single-phase quasicrystalline alloy. The sintered single-phase alloy showed a higher microhardness in comparison with the DS coatings.

In the current practice of applying carbide-based coatings by thermal spraying, the starting material usually contains a metal binder. However, it is important to study the possibility of spraying binder-free carbides, since the metal components usually reduce the operating temperature and corrosion resistance of cermet coatings. In this work, a powder of chromium carbide, Cr3C2, was sprayed using a CCDS2000 detonation gun. Acetylene–oxygen mixtures C2H2 + kO2 with k varying from 0.8 to 3.0 were used as an energetic material. Due to chemical reactions between Cr3C2 and the detonation products, the coatings were of composite nature (multi-phase materials) with a composition depending on k. At k values in the range from 0.8 to 1.1, along with Cr3C2, the coatings contained chromium carbonitride Cr3N0.4C1.6. In the k range from 1.3 to 2.0, Cr7C3 and Cr were the main components of the coatings. As k was increased to 3.0, along with Cr7C3 and Cr, the CrO and Cr2O3 oxides formed in the coatings. The mechanical properties and wear resistance of the coatings were found to depend on their phase compositions. Coatings produced by detonation spraying of Cr3C2 powder may be useful for increasing the corrosion resistance of machine parts to mineral acids and high-temperature oxidation resistance.

Hydroxyapatite (HA), the major mineral component of tooth enamel and natural bones, is a good candidate for bone tissue engineering. Synthetic HA is used for making coatings on metallic implants intended for medical applications. A HA coating renders the implant biocompatible and osteoinductive. In addition, it improves fixation and the overall performance of the implanted object. In the present work, HA coatings were deposited on a medical titanium alloy implant with mesh geometry and a developed surface by detonation spraying. The feedstock powder was HA obtained by the dry mechanochemical method. Single-phase HA coatings were obtained. The coatings were formed not only on the surfaces normal to the particle flow direction, but also on the sides of the mesh elements. Despite partial melting of the powder, no decomposition of HA occurred. This work demonstrates the prospects of detonation spraying for the production of HA coatings on metallic implants with complex geometries.

On the CCDS2000 installation, detonation spraying of coatings from M28 and METCO 6103 aluminum oxide powders on steel substrates was carried out, and the dependence of the electrical resistivity of coatings on the atmosphere humidity was studied. It is shown that when the relative humidity changes from 14 to 80%, the specific electrical resistance of the coating decreases by 2-3 orders of magnitude from ρ ˃1013 Ω·cm to ρ ≈ 1011 Ω·cm. On the base of obtained data, the model of coating microstructure is proposed, according to which alumina layer contained through defects in a form of nanochannels with diameter in the range 1-10 nanometers. In a coating cross section, the area of nanochannels sums up to 1%. In presence of high atmospheric humidity, these nanochannels can be filled with absorbed water, increasing drasticcaly the coating electrical conductivity.

In thermal spraying of refractory metal powders, two major issues need to be solved: particles of materials having high melting temperatures should be heated to reach a semi-molten/molten state or temperatures close to the melting point, while oxidation of the metals should be prevented. It has long been believed that it is rather difficult, if not impossible, to produce high-quality refractory metal coatings by detonation spraying. In this work, we demonstrated the capability of the detonation spraying method to produce tantalum-based and molybdenum coatings of low porosity. Using a computer-controlled detonation spray (CCDS2000) facility, the detonation spraying behaviour of a molybdenum powder and a partially oxidized tantalum powder was studied. Spraying was conducted onto steel substrates using an acetylene-oxygen mixture with O2/C2H2 = 1.1. The spraying process was studied by means of analyzing the splat morphology and calculating the particle temperatures and velocities. According to the X-ray diffraction phase analysis, the metals did not experience oxidation during the deposition. Rather, partial reduction of the oxide phase contained in the Ta-based powder occurred during spraying.

The analysis of material flow fields under the explosive collapse of two-layer metal/ceramics tubes is carried out. It is shown that the main reason for the absence of condensed jet is the explosion evaporation of the inner metal layer due to ultra-high temperatures in the compression area. For the case of the copper inner layer, very interesting and extraordinary features of the flows are observed. The non-stationarity of the process during the entire tube compression period attracts attention. The copper density at the point of contact decreases to 6.06 g/cm3 to the moment of time of 13 µs. This can only mean that copper is already partially vaporized before the collision point. To produce condensed hypervelocity jets, it is proposed to use a material of the inner layer with a high evaporation temperature. The analysis of properties of existing materials shows the perspective of using such refractory and plastic metals as niobium and tantalum as an inner layer of the tube.

Detonation spraying of WC/Co was conducted with two-component fuel using a computer-controlled detonation spraying system. The in-flight temperatures and velocities of the particles were calculated and optimized for C2H2/C3H8/O2 and C2H2/C4H10/O2 detonation gas mixtures. The stable spraying mode was realized in a short gun barrel thanks to the formation of a stratified explosive charge by means of precise computer-controlled supply of the gas components. The stand-off distance was varied from 50 to 400 mm and the substrate tilt angle relative to a plane normal to the spraying direction was varied from 0 to 60°. The formation of splats was analyzed to determine the optimal spraying mode. The microstructure and porosity of the coating were studied, and microhardness, bonding strength and wear resistance were measured. It was found that spraying with two-component fuels produces coatings with enhanced properties. For the WC-12 wt.%Co coatings, the following characteristics were achieved: porosity of G65 abrasion wear of

The present work was aimed to demonstrate the possibility of forming Fe66Cr10Nb5B19 metallic glass coatings by detonation spraying and analyze the coating formation process. A partially amorphous Fe66Cr10Nb5B19 powder with particles ranging from 45 &micro, m to 74 &micro, m in diameter was used to deposit coatings on stainless steel substrates. The deposition process was studied for different explosive charges (fractions of the barrel volume filled with an explosive mixture (C2H2 + 1.1O2)). As the explosive charge was increased from 35% to 55%, the content of the crystalline phase in the coatings, as determined from the X-ray diffraction patterns, decreased. Coatings formed at explosive charges of 55&ndash, 70% contained as little as 1 wt.% of the crystalline phase. In these coatings, nanocrystals in a metallic glass matrix were only rarely found, their presence was confined to some inter-splat boundaries. The particle velocities and temperatures at the exit of the barrel were calculated using a previously developed model. The particle temperatures increased as the explosive charge was increased from 35% to 70%, the particle velocities passed through maxima. The coatings acquire an amorphous structure as the molten particles rapidly solidify on the substrate, cooling rates of the splats were estimated. The Fe66Cr10Nb5B19 metallic glass coatings obtained at explosive changes of 55&ndash, 60% showed low porosity (0.5&ndash, 2.5%), high hardness (715&ndash, 1025 HV), and high bonding strength to the substrate (150 MPa).

The possibility of obtaining alloy/composite coatings by detonation spraying of Fe + Co + Ni and Fe + Co + Ni + Cu powders mixtures was evaluated for the first time. The conditions of spraying were selected such that the particles of all three (four) metals were flying out of the gun barrel in the fully molten state, as confirmed by the calculated particle temperatures. The deposited layers had a dense composite structure consisting of metallic lamellae. A common feature of the deposited layers was a diminished concentration of iron relative to the feedstock mixtures. The results of the present work show that, upon a proper adjustment of the composition of the feedstock mixture, detonation spaying can be used to form dense precursors of high-entropy alloy coatings.

Tungsten is a promising material for plasma-facing components of thermonuclear reactors. In the present work, tungsten coatings of low residual porosity (1%) were deposited on copper substrates by detonation spraying. Calculations of the particle temperatures and velocities were conducted for tungsten particles of different sizes using a previously developed model. These calculations helped selecting the spraying parameters enabling the formation of high-quality tungsten coatings in the experiments. A proper selection of the stand-off distance allowed achieving a high deposition efficiency of the powder (60%). The coatings showed a high bonding strength to the copper substrates, which was found to be 100 MPa, and a high hardness (850 HV). The coatings were shown to accumulate compressive stresses, which are beneficial for the structural integrity of coatings up to 500 μm thick.

In this work, the spraying behavior of a copper powder in the Computer-Controlled Detonation Spraying (CCDS) process was studied both theoretically and experimentally. The dependences of the particle temperatures and velocities on the explosive charge were calculated for particles of copper 40 μm in diameter for different O 2 /C 2 H 2 ratios (1.1; 1.5; 2.0; 2.5) and nitrogen and air as carrier gases using models and software previously developed at Lavrentyev Institute of Hydrodynamics SB RAS. The explosive charge was varied between 30 and 60% of the barrel volume. Calculations showed that the particle temperatures increase and the particle velocities decrease monotonously as the O 2 /C 2 H 2 ratio increases from 1.1 to 2.5 at a constant explosive charge when nitrogen is used as a carrier gas. It was shown that the choice of the carrier gas (nitrogen or air) significantly influences the temperature of the particles when spraying is conducted at a low O 2 /C 2 H 2 ratio. In this case, the particle velocities are also affected. For experiments, an electrolytic copper powder with an average size of 40 μm was used. The morphological features of the deposits were such that could be well expected in the deposits formed by particles heated up to the calculated temperatures.

Detonation (D-gun) spraying uses detonation of hydrocarbon fuel to heat and accelerate the powder particles. Spraying using incomplete combustion can lead to changes in the composition of the sprayed material due to the presence of the in-situ formed carbon particles in the spraying atmosphere. In this work, we have studied the phase formation of the deposits obtained by D-gun spraying of Ni and “Ni-amorphous carbon mixtures”. It was found that solid solutions based on metastable hcp-Ni and fcc-Ni form in detonation deposits at O 2 /C 2 H 2 =0.7 and explosive charges of 50–70%. No metastable phases were found in the coatings sprayed at O 2 /C 2 H 2 greater than 1.1. Microstructural and elemental analyses confirmed that the in-situ formed carbon is preferentially incorporated in molten Ni particles. Carbon ex-situ introduced into the feedstock powder changes the sprinkling conditions of the melt over the substrate surface and lowers the cooling rate of the molten particles. As a result, deposits obtained at an explosive charge of 60% and 70% from powders containing added carbon tend to show lower concentrations of the hcp phase compared with deposits obtained from Ni.

Progress in design of thermal barrier coatings (TBCs) is based upon application of new materials and deposition techniques. In this work traditional NiCrAl bond coat YSZ top coat were deposited on Ni superalloy substrate by inexpensive dry detonation spraying, while finishing layers of oxide nanocomposites (LaAlO3–La2Zr2O7, LaAlO3–LaCuAl11O19) were deposited on YSZ by slip casting. Complex oxides were prepared via Pechini route. Thin (~ 20 μm) finishing layers were deposited by slip casting of suspensions of oxides mixture in isopropanol with addition of polyvinylbutyral. Genesis of the texture, composition and real/defect structure of bulk nanocomposite materials and deposited layers after annealing in air up to 1300 °C as well as after series of thermal shocks by heating up to 1200 °C by H2–O2 burner were studied by combination of diffraction (high resolution SEM and TEM with EDX, XRD on synchrotron radiation) and spectroscopic (UV–Vis, EXAFS, laser-excited Dy3 + luminescence spectra) methods. Thermal conductivity of nanocomposites and TBCs was determined by using NETZSCH LFA 457 MicroFlash. Nanocomposites were shown to retain porosity as well as nanosizes of disordered domains of oxide phases even after sintering at high temperatures. A good adhesion and compatibility of all layers in TBCs were demonstrated, while in general disordering of the oxides structure in deposited layers was higher than that in bulk materials due to the effect of depositing procedure and interaction between layers. This provides a low thermal conductivity of nanocomposites and functionally graded TBC. After 90 thermal shocks neither layers spallation nor cracks were revealed, 8YSZ and finishing layers retaining porosity, nanocrystallinity and disordering required for a low thermal conductivity and cracks trapping.

One of the trends in hydrogen power engineering is the development of devices for the preparation of synthesis gas by the catalytic reforming of a hydrocarbon feedstock. Studies show the advantages of catalytic converters based on a modular catalyst support with a honeycomb-type structure produced from a metal foil, both sides of which are coated with highly porous oxide ceramics. The drawback of this design is a poor ability of the coating to withstand high-temperature operating conditions. The coating may detach from the substrate because of the difference in thermal expansion coefficients between the metal foil and the ceramic coating. Besides, a corrosion of metal foil takes place. The result of the present study is the development and application of a two-step coating method, which allows significantly increasing the service life of the catalyst supports. At the first step, a low-porosity ceramic layer is deposited on a metal foil by detonation spraying. At the second step, a high-porosity layer of a...

The phase composition and microstructure of coatings formed by detonation spraying of Ti-Cu powder mixtures using C2H2 + kO2 explosive charges with k varying from 0.7 to 2.0 were studied. The Ti-Cu system was selected to demonstrate the possibilities of forming metal matrix composites (MMCs) with in-situ synthesized ceramic particles during the coating deposition. The formation of composite microstructures needs to be considered when obtaining carbon-containing MMCs by detonation spraying using acetylene-oxygen mixtures at k ˂ 1. The focus of the present study is the phase formation, microstructure development and hardness variation of the coatings caused by carbon, oxygen and nitrogen uptake by the Ti-Cu mixtures during spraying. Carbon released in the form of graphene nanoplatelets as a result of incomplete combustion of acetylene at k = 0.7 reacted with titanium, and, in the presence of nitrogen (a carrier gas), the TiCxNy phase formed in the coatings. Copper was found to play a protective role, reducing the conversion degree of titanium into the ceramic phases. Deposits containing 21 – 44 wt.% of ceramic components formed when an explosive charge equal to 50% of the gun barrel volume was used, the nature and concentration of the ceramic phases depending on k. At k = 2.0 and an explosive charge of 50%, a composite coating reinforced with Ti2O3, TiO and TiN (comprising 41 wt.% in total) was obtained. This composite showed a microhardness of 480 HV, which was due to a high content of ceramic phases synthesized in situ during spraying.

In this work, the formation of coatings by chemical reaction-accompanied detonation spraying of TiC x –Ti composite powders differing in the microstructure and carbon content was studied. The powders were synthesized by a reaction between titanium and carbon in the presence of excess of titanium via self-propagating high-temperature synthesis followed by mechanical milling with an additional amount of titanium (which produced a composite product containing 4.2 wt% of carbon) or by thermal annealing of mechanically milled mixtures containing 2.1 wt% of carbon. It was found that in the detonation coatings, the relative amount of metallic titanium dramatically decreased in comparison with the powders due to its reactions with carbon and nitrogen contained in the spraying atmosphere and the formation of titanium carbonitrides TiN v C w . It was possible to distinguish regions in the cross-section of the coatings with a composite microstructure inherited from the powders and with a microstructure in situ formed by the products of chemical reactions that occurred during spraying. The volumes of the material with the in situ formed microstructure contained the major fraction of the porosity of the coatings. The average hardness of the TiC x –TiN v C w –Ti coatings ranged between 400 and 480 HV. Despite higher porosity of the coatings formed at higher degrees of chemical transformation, their average hardness increased. No significant differences in the hardness of the coatings produced from two feedstock powders were observed. The similarity between the coating formation processes from two TiC x –Ti powders of different microstructures and the similarity of those to the coating formation process from a metallic titanium powder show that the reactivity of titanium during detonation spraying is a crucial factor determining the coating microstructure and properties.

The phase development in the coatings formed by detonation spraying of titanium in a wide range of compositions of the spraying atmosphere is reported. The phase composition of the coatings was found to be very sensitive to the O 2 /C 2 H 2 ratio and the nature of the powder carrier gas. Using O 2 /C 2 H 2 = 1.1 and air as a carrier gas, titanium oxynitride-containing coatings were obtained, while at O 2 /C 2 H 2 = 2.5, titanium oxides were the reaction products. In highly reducing conditions at O 2 /C 2 H 2 = 0.7 and with the use of nitrogen as a carrier gas, titanium carbide and carbonitride formed. Higher contents of nitrides in the coatings were found when nitrogen was added into the O 2 + C 2 H 2 mixture. Metal-ceramic coatings formed at high transformation degrees of titanium were either composed of metallic titanium-rich particulate agglomerates distributed in a ceramic-rich matrix or contained alternating layers rich in metallic titanium and rich in ceramic compounds.

The goal of this work was to study the phase and microstructure changes involved in the process of coating formation by detonation spraying of Ti3Al, TiAl, and TiAl3 intermetallics. The O2/C2H2 ratio was varied between 1.1 and 2.0, and the explosive charge was 30–40% of the barrel volume. In most experiments air was used as a carrier gas; selected experiments were performed with argon. We found that depending on the spraying parameters, TiAl3 essentially retains in the coatings or partially decomposes forming TiAl and Ti3Al as minor phases. Detonation sprayed Ti3Al reacts with nitrogen and oxygen partially transforming into titanium nitrides TiN/Ti2N and titanium oxynitrides TiNxOy. TiAl partially decomposes forming Ti3Al, which further reacts with oxygen and nitrogen as the particle temperature and the content of oxygen in the explosive mixture increase. The in situ formed titanium nitrides and oxynitrides show a reinforcing effect increasing the hardness of the coatings.

In thermally sprayed coatings, nano-sized features of the microstructure may be either inherited from the nanostructured agglomerates of the feedstock powder or form as a result of rapid cooling of molten particles upon deposition. Applying a process of the computer-controlled detonation spraying (CCDS) to Ti3SiC2-Cu composite powders produced by high-energy mechanical milling, we show that both routes are possible depending on the spraying conditions. When the nanostructure of the Ti3SiC2-Cu coating is inherited from the feedstock powder—under very mild conditions of detonation spraying, which exclude melting, so is the phase composition of the coating. In higher-temperature conditions of spraying, a significant fraction of the copper matrix melts and the interaction between Ti3SiC2 and Cu occurs. The TiC x -Cu(Si) coatings that form show crystallites of both phases in the nano-range. In this case, rapid solidification of the molten fraction of the particles is responsible for the formation of the coatings with a nanostructured matrix. Due to the flexibility of the CCDS process, conditions of spraying were found such that a composite coating with very fine crystallites of the Cu(Si) matrix (30 nm) and a hardness of 273 HV could be obtained.

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.

This article is a focused review aimed to describe the potential of the computer-controlled detonation spraying (CCDS) for producing and designing coatings with variable chemical and phase compositions and microstructure and promising properties. The development of the detonation spraying method is briefly analyzed from a historical perspective and the capabilities of the state-of-the art facilities are presented. A key advantage of the CCDS is the possibility of using precisely measured quantities of the explosive gaseous mixtures for each shot of the detonation gun and different oxygen to fuel ratios, which can create spraying environments of different chemical properties—from severely oxidizing to highly reducing. The significance of careful adjustment of the spraying parameters is shown using material systems that are chemically sensitive to the composition of the spraying environment and temperature. Research performed by the authors on CCDS of different materials—metals, ceramics, intermetallics and metal-ceramic composites is reviewed. Novel applications of detonation spraying using the CCDS technology are described.

The structure and mechanical properties of the coatings formed by reactive detonation spraying of titanium in a wide range of spraying conditions were studied. The variable deposition parameters were the nature of the carrier gas, the spraying distance, the O2/C2H2 ratio, and the volume of the explosive mixture. The phase composition of the coatings and the influence of the spraying parameters on the mechanical properties of the coatings were investigated. In addition, nanohardness of the individual phases contained in the coatings was evaluated. It was found that the composition of the strengthening phases in the coatings depends on the O2/C2H2 ratio and the nature of the carrier gas. Detonation spraying conditions ensuring the formation of composite coatings with a set of improved mechanical properties are discussed. The strength of the coatings was determined through the microhardness measurements and local characterization of the phases via nanoindentation. Three-point bending tests were employed in order to evaluate the crack resistance of the coatings. The strengthening mechanisms of the coatings by oxide or carbonitride phases were discussed. © 2017 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

We have examined the new phase formation and compositional variations in the coatings produced by detonation spraying of Ti3Al powders in atmospheres of different chemistry. The composition of the spraying atmosphere was varied by changing the O2/C2H2 ratio used for the detonation. In the coatings sprayed at an O2/C2H2 ratio of 0.87 and 1.05, certain deviations of the Al/Ti ratio have been observed relative to the sprayed powder. In these coatings, the Ti3Al phase was found along with TiN and Ti2N formed due to the reaction of the heated particles with nitrogen used for powder injection. The amount of TiN increased with increasing explosive charge and a concomitant rise in the particles temperature. Under O2/C2H2 ratios equal to 1.50 and 2.00, significant losses of Al were detected, the coatings being composed mainly of titanium oxides. This study shows that detonation spraying conditions excluding severe oxidation of Ti3Al can be found as well those facilitating oxidation with an associated loss of Al in the deposits.

Composite WC/Co + MoS 2 coatings were deposited onto steel substrates by Computer Controlled Detonation Spraying using three spraying modes: very cold, cold and normal. Maximal content of MoS 2 in a sprayed powder was 10 wt.%. Characterization of coatings was made with chemical and phase analyses, microhardness measurement, morphology and microstructure investigation. X-ray diffraction study shows that residual MoS 2 exists only in coatings obtained at very cold and cold spraying modes. At normal spraying mode complete decomposition of the solid lubricant occurs during spraying. From the engineering point of view, the coating applied at the cold mode using a powder containing 10 wt.% MoS 2 is the most promising. Such a coating has microhardness of 650 HV 0.2 and a porosity of 10%.

In the present work, rutile powders containing additions of metallic silver (2.5 vol.%) were detonation sprayed in a reducing atmosphere formed by gaseous detonation products of the C2H2 + 1.05O2 mixture. The initial volume of the C2H2 + 1.05O2 mixture – explosive charge – used for a detonation pulse was computer-controlled as the fraction of the barrel volume filled with the mixture. Using a previously developed model of the detonation process, the particle temperatures and velocities were calculated to explain the observed phase and microstructure development in the coatings. With increasing explosive charge, the temperature of the sprayed particles increased and rutile was partially reduced to oxygen-deficient TiO2−x and then to Ti3O5. When the melting temperature of rutile was not reached, the coatings were porous; semi-molten particles formed denser coatings obtained with higher spraying efficiency. Silver inclusions in the titanium oxide matrix experienced melting and substantial overheating, but remained well preserved in the coatings.

Detonation spraying is a well-known technology which is applied for deposition of diverse powders, in particular cermets, to form various protective coatings. Actual progress is related to a recently developed technique of computer-controlled detonation spraying and its application in non-traditional domains as development of composite and graded coatings or metallization of plastics. The gas detonation parameters are analyzed to estimate the efficiency of different fuels to vary particle-in-flight velocity and temperature over a broad range thus providing conditions to spray diverse powders. A particle of a given nature and fixed size could be sprayed in a solid state or being strongly overheated above the melting point by variation of the quantity of the explosive gas mixture which is computer-controlled. Particle-in-flight velocity and temperature are calculated and compared with jet monitoring by a CCD-camera-based diagnostic tool and experimental data on splats formation.

Structural characterization of detonation deposits formed by reaction products of titanium with the components of the spraying atmosphere showed that ceramic-based coatings of unique microstructures—consisting of alternating layers of different compositions—can be formed. For the first time, mechanical characteristics of the coatings formed by reaction-accompanied detonation spraying of titanium were evaluated. It was found that high-yield transformation of titanium into oxides and nitrides during spraying can result in the formation of coatings with high fracture resistance and interface fracture toughness. The hardness of the coatings measured along the cross-section of the specimens was higher than that on the surface of the coatings, which indicated mechanical anisotropy of the deposited material. In terms of mechanical properties, coatings formed by the reaction products appear to be more attractive than those specially treated to preserve metallic titanium.

Structured catalysts based on metallic supports of different types with a high thermal conductivity were designed. The metal monolithic supports were made from a heat-resistant foil or gauze coated with a protective layer of Al 2 O 3 or zrO 2 using blast dusting. To prepare catalysts, Ce-Zr-La-O and LaNiO x promoted with Pt were successively supported on monoliths. A high and stable performance of these catalysts in the partial oxidation of methane (POM) at short contact times in the autothermal mode was demonstrated. In the reactor with a heat exchanger these catalysts operate in the autothermal mode without any heat preheat at very high gas velocities.