Three different coatings were deposited using the Detonation Gun Spraying (DGS) technology from steel powders alone, and steel powers mixed with Fe3C and SiC particles, respectively. The microstructural characteristics of these coatings were examined and the hardness of each type of coating was studied. The morphology and structure of the feedstock powders were affected by the exposure to high temperature during the spraying process and rapid solidification of steel powders that resulted in the formation of an amorphous structure. The unreinforced steel coating had the highest hardness among the three types of coatings, possibly due to a higher degree of amorphization in the coating compared to the other two samples. The microstructural observation confirmed the formation of dense coatings with a layered structure with good connectivity between layers with minimum defects and porosities in the interfacial regions.

A wide range of properties can be achieved in intermetallic coatings applied by gas detonation spraying (GDS). The properties of Fe-40at%Al GDS layers, however, may change when exposed to temperatures exceeding a threshold level. To characterize such changes, Fe-40at%Al GDS coatings were subjected to systematic dilatometric studies in which temperatures were cycled from room temperature to 1180 °C. The investigation revealed both irreversible and reversible phase transitions as described in the paper. Dilatometry measurements obtained from sintered samples made from the same powder are presented for comparison.

This study compares the microstructure of Al 2 O 3 coatings produced by detonation gun spraying (DGS) and laser stereolithography (SLA). The SLA samples mostly consisted of alumina and voids, while the DGS-deposited alumina contained additional features such as splats, pores, cracks, and boundaries. DGS deposits were also denser with about 3% porosity compared to 8% porosity in the SLA samples. EDS analysis showed that both coatings contained only aluminum and oxygen, although additional carbon was detected in the SLA samples, indicating the presence of residual binder (resin based) material. XRD analysis revealed a mixture of α and γ-Al 2 O 3 phases in the DGS coatings, but no phase change in the SLA samples.

While depositing Fe-Al intermetallic powders applying a gas detonation spraying a certain coating structures containing oxide ceramics are created. These structures exhibit both extreme mechanical resistance and unusual thermophysical properties (TP) also. One of such property is relatively low thermal conductivity. A possible application as thermal barrier coatings needs precise determination of TP dependence on temperature and resistance of the coating structure to temperature exposition. At present study TPs were investigated for a coating produced from Fe-Al intermetallic powder in a course of complex measurements including DSC analyses, laser flash thermal diffusivity measurements, dilatometric studies complemented with microstructural analyses. The study resulted in full characterization of the investigated structure TPs: density, thermal expansivity, heat capacity and thermal conductivity. During thermal analyses interesting phenomena concerning thermal resistance to the temperature exposition of the investigated coating were revealed. The obtained results complement rather sparse literature data on TPs in that subject and contribute to better understanding of gas detonation spraying (GDS) process technology and intermetallic/oxide structures property understanding.

The paper reports the results of structure examination of intermetallic Fe-Al type coatings obtained by the detonation gun spraying on a C45 plain carbon steel substrate. The structure was analysed with scanning (SEM), transmission (TEM) electron microscopy techniques and electron (SAE) and X-ray diffraction methods as well as quantitative inspection of composition in microareas (EDX). Special attention was paid to the interface between the coating and the substrate analyzing particularly the substructure of the individual grains contained up to 15μm away from the substrate surface layer. The results allowed explaining the formation mechanism of the coating morphology with a contribution of intermetallic phases Fe 3 Al, FeAl, FeAl 2 and Fe 2 Al 5 as well as the ε phase taking into consideration the influence of velocity, temperature and pressure on the powder particles during the D-gun spraying. It was established that the coating produced with the DGS method had sublayer morphology of alternate flattened and partially melted grains with wide range of Al content from 39 up to 63 at.%. Partial melting of the individual powder particles brought about the appearance of the amorphous grains and subsequently columnar crystals of the Fe-Al type phases formed sequentially at the interface area coating and cold substrate surface layer material, which was essential in the mechanism of the Fe- Al coating formation. It was established, that in the area of the polycrystalline dispersive structure formed from the highly plasticized FeAl grains during D-gun spraying, complex oxide films identified as Al 2 O 3 -γ formed, serving as specific composite reinforcement in the intermetallic Fe-Al coating. A mechanism of crystallization of partially melted Fe-Al particle containing nominally 63 at.% Al was carried out in the work in an attempt to explain the formation of different sub-layers within the Fe-Al intermetallic coating at the interface 045 steel surface layer.

The dynamic properties and thermal history of FeAl particles were estimated and assessed in this study. First, parameters of the detonation process for the investigated mixture were calculated using a thermochemical code. Next, the motion parameters and thermal history of the analyzed powder particles were assessed using computational fluid dynamics software and algorithms developed by the investigators. The appropriate models allowed for determination of melted volume (mass) fraction of a certain analyzed single particles that have diameters ranging from 10 to 160 μm. The results show that only the smallest particles melt under the investigated conditions. Moreover, the estimated radial distribution of the temperature inside the particles is almost homogeneous due to the relatively high FeAl thermal conductivity and relatively low thermal conductance of surface heat transfer. The calculated particle terminal velocity was compared to experimental data and to data from previous studies in the literature to determine the accordance of results among the data sets.

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.

Well-known detonation thermal spraying is considered to be a good method for the preparation of WC-based coating with high adhesion. The depositing parameters, especially the oxygen-fuel ratio and spot frequency, have been observed to influence the properties of the coating. The influence of the main parameters of the detonation spraying of tungsten carbide based coatings and their mechanical properties have been investigated. Two main tasks for the development of a carbide-containing material application technology have been determined. The relationship between the phase composition of WC-based coatings and their strength, hardness and bond strength to the substrate has been identified. The technique of coating in the reductive mode has been proposed. High oxygen-fuel ratio and spot frequency decreased the decomposition of the WC-phase, which makes the WC-Ni particles harder and as a result more easily embedded in the substrate, i.e. the coating which is beneficial to enhance bonding strength.

In the present work, a metal-polymer composite coating containing Al and ethylene-vinyl acetate copolymer (EVA) was prepared on the surface of a polymer matrix composite (PMC) using a detonation spraying process. The microstructure and bond strength of the as-prepared coatings were analyzed. The bonding mechanism of the coatings, especially the deposition behavior of the Al and EVA particles on the PMC surface is discussed. Results had shown that detonation spraying technique enables the deposition of metal-polymer coatings directly onto the PMC surface under precise process control. The preparation of metal-polymer composite coating on PMC via detonation spraying process presents promising application as an interlayer for the surface metallization of PMC.

Detonation spraying is used for applying metal, cermet, polymer and ceramic coatings. The advantages of this technology include good adhesion and density of coatings. Minimal residual stresses in the spray process give the possibility to apply coatings to thin-walled parts and foil. Numerical modeling methods for energy parameters of powder particles give the possibility to predict the interaction of powder particles with the gas flow in and properties of coatings depending on spray parameters. In many cases, existing advantages such as high quality of coatings, little heating of the substrate, efficient and economical use of the powder, make the detonation spray process more attractive in comparison with other spray methods. The new design of D-Gun and software gives the possibility to overcome these limitations and significantly increase the productivity. This result was obtained due to a new design of the valve head, new computer control system, electronics and software that allows the firing rate frequency to be increased, ensure the reliability and extend the maintenance-free lifetime. The paper discusses the results of modeling of acceleration and heating the particles of powders in the new detonation system and also methods of computer simulation of the formation of adhesive contact between powder particles and metal surface.

Although detonation sprayed coatings are harder and better adhered than those achieved by plasma and even HVOF spraying, the method is far less used due to productivity and equipment challenges associated with mechanical valving and intermittent powder flows. This study shows how the use of propane as a fuel eliminates the need for mechanical valving and allows for continuous powder feeding through a high-frequency detonation spray gun. To demonstrate the capabilities of valveless detonation spraying, WC-CoCr powders were deposited under different conditions (oxygen-to-fuel ratio, flow rate, shot frequency) and the resulting coatings were assessed based on porosity, microhardness, deposition efficiency, and phase composition.

This paper describes the basic design and operation of a multi-chamber detonation sprayer (MCDS) and explains how it differs from conventional detonation sprayers and other spraying methods. It presents and analyzes ceramic, metal, and cermet coatings produced with the new sprayer, highlighting its ability to deposit low-melting point and refractory materials. It compares the efficiency and operating costs of the MCDS with some of the more common HVOF torches and reviews the coating properties that have been achieved with different powders and spraying parameters.

In the present study, a new multi-chamber detonation sprayer (MCDS) was used to deposit Al 2 O 3 coatings on titanium and carbo steel substrates. SEM, TEM, and XRD analysis of the layer between the coating and substrate revealed the presence of an intermetallic compound that improves coating properties and is conducive to the relaxation of stresses generated during spraying.

This study investigates the influence of substrate preheating on the microstructure, hardness, and adhesion of detonation sprayed WC-CoCr coatings. Using commercially available powders, coating samples are deposited on low carbon steel substrates, some at room temperature and some having been preheated to 300°C. Test results show that the coatings deposited on preheated substrates are harder, more crack resistant, and better adhered, with no significant differences in microstructure. After tensile testing, fracture surfaces and interfaces were investigated, showing how fracture behavior, along with hardness and bonding strength, correlate with phase composition and particle impact conditions.

In this study, a multi-chamber detonation sprayer is used to deposit cermet coatings on flat specimens of corrosion-resistant steel. It is shown that the sprayer provided conditions for the formation of dense WC-CoCr, CrC-NiCr, and CrC-TaC-NiCr layers, ranging in thickness from 80-375 μm, with low porosity, high microhardness, and low wear rates.

Detonation-gun thermal spray technique was used to deposit commercial available Ni-20Cr and WC-Co coatings on ASTM A213 TP347H boiler steel. The coated specimens were subjected to air environment at 900°C in laboratory furnace to determine high temperature oxidation resistance. Mass change data was recorded to formulate oxidation kinetics of both the coated specimens. The exposed specimens were assessed by field emission scanning electron microscopy and energy dispersive spectroscopy (FE-SEM/EDS) and XRD analysis. The primary focus of the study is attractive oxidation resistance of Detonation gun sprayed Ni-20 Cr coating over the WC-Co coating on the said steel in the air environment.

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 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.

In this study, detonation spraying was used to deposit commercially available Ni-20Cr and WC-Co powders on SA213-T22 boiler steel. Coated and uncoated specimens were subjected to 50 thermal cycles in a molten salt boiler environment 900 °C in order to evaluate their hot corrosion behavior. Mass change measurements were made at the end of each cycle to assess corrosion kinetics and XRD and SEM/EDS were used to characterize corrosion products. An analysis of the reaction kinetics and the formation of oxide scales is provided in the paper.

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.