Thermal Spray Research Articles

Prediction of HVAF thermal spraying parameters and coating properties based on improved WOA-ANN method

In this study, high-velocity air fuel (HVAF) thermal spray technology was utilized to deposit Hastelloy C276 powder onto 316 L stainless steel substrates. The effects of various spray process parameters such as propane pressure, air pressure, spray distance, and powder feeding rate on the microstructure, microhardness, and corrosion resistance of the coatings were investigated. In addition, the coupling effects among multiple spray parameters were considered by employing a combined approach with the Improved Whale Optimization Algorithm (IWOA) and Artificial Neural Network (ANN) model, and the mapping relationships between the spray process parameters and coating porosity, microhardness, and corrosion current density was established. The results revealed that the prepared C276 coating exhibits lower porosity, higher microhardness, and exceptional corrosion resistance. And the IWOA-ANN model outperforms the ANN model and WOA-ANN model in the prediction accuracy and stability for all three performance measures, particularly for porosity and microhardness. Furthermore, the comparison between experimental results and predicted results validates the reliability and accuracy of the trained IWOA-ANN model, demonstrating its efficacy in predicting HVAF spray parameters and coating properties.

Tribological performance of functional coated fiber reinforced additively manufactured polymer composite

Additive manufacturing has witnessed an upward trend in utilization across diverse industries in recent years. This study examines the tribological properties of polymer composites produced using additive manufacturing. The polymer composites were produced using the fusion deposition modeling process. Subsequently, they undergo thermal spray coating and spin coating processes that deposit hafnium carbide particles onto their surface. The wear test studies were conducted at three distinct temperature levels in accordance with the ASTM standard procedure. The findings demonstrated that the application of a ceramic particle coating led to a substantial decrease in the specific wear rates. Additionally, there were observed differences in the wear rates depending on the specific methods used for applying the coating. The application of thermal coating shown high efficacy in reducing wear rates and safeguarding the underlying materials against material loss. The uncoated carbon fiber reinforced polylactic acid (PLA-CF) material showed a slightly significant amount of material degradation as the test chamber temperature increased, in comparison to the coated specimens. The average specific wear rate of the thermally coated carbon fiber reinforced polylactic acid specimen at a temperature of 70 °C is 0.000156 kg Nm−1.

Improvement of heat resistance in silicone rubber by Fe-doped TiO2 nanoparticles prepared via flame spray pyrolysis

In recent years, the development of heat-resistant silicone rubber has been a research hotspot. In this paper, a kind of Fe doped TiO2 nanoparticles (Fe-TiO2) was prepared via flame spray pyrolysis, which can significantly improve the high temperature resistance of silicone rubber. The results show that, on the one hand, the prepared Fe-TiO2 can inhibit the breakage of Si-O main chain; on the other hand, because Fe is doped into the lattice of TiO2, it causes the change of TiO2 crystal phase and produces more oxygen vacancies, which is more beneficial to capture free radicals in silicone rubber matrix, so that Fe-TiO2 can effectively inhibit the excessive cross-linking of silicone chain caused by methyl oxidation on the side of silicone rubber. TGA results showed that after adding Fe-TiO2, the 5 % thermal weight loss temperature of methyl vinyl silicone rubber increased from 392.8 °C to 435.6 °C.

Performance of Atmospheric Plasma-Sprayed Thermal Barrier Coatings on Additively Manufactured Super Alloy Substrates

This work represents a preliminary study of atmospheric plasma-sprayed (APS) Yttria-Stabilized Zirconia (YSZ)-based thermal barrier coatings (TBCs) deposited on forged and additive manufactured (AM) HAYNES®282® (H282) superalloy substrates. The effect of different feedstock morphologies and spray gun designs with radial and axial injection on APS-deposited YSZ layer characteristics such as microstructure, porosity content, roughness, etc., has been investigated. The performance of TBCs in terms of thermal cycling fatigue (TCF) lifetime and erosion behaviour were also comprehensively investigated. In view of the high surface roughness of as-built AM surfaces compared to forged substrates, two different types of NiCoCrAlY bond coats were examined: one involved high-velocity air fuel (HVAF) spraying of a finer powder, and the other involved APS deposition of a coarser feedstock. Despite the process and feedstock differences, the above two routes yielded comparable bond coat surface roughness on both types of substrates. Variation in porosity level in the APS topcoat was observed when deposited using different YSZ feedstock powders employing axial or radial injection. However, the resultant TBCs on AM-derived substrates were observed to possess similar microstructures and functional properties as TBCs deposited on reference (forged) substrates for any given YSZ deposition process and feedstock.

Feasibility research of perovskite‐type PrAlO3+δ as high‐temperature infrared radiation coating

AbstractThermal radiation coating with low thermal conductivity and high infrared emissivity are desirable. In this work, a novel rare‐earth aluminate (PrAlO3+δ with rhombohedral structure) was synthesized via solid‐state reaction method, and the corresponding coating was fabricated using atmospheric plasma spraying (APS). The study encompassed an investigation into the phase structure, high‐temperature phase stability, thermo‐mechanical characteristics, and infrared properties. The results illustrate that as‐deposited coating contained amorphous phase, but recrystallized coating presented phase stability up to 1600°C. Furthermore, the recrystallized coating exhibited low thermal conductivity of 1.35 W/m K at 900°C as well as an average coefficient of thermal expansion of 10.36 × 10−6/K. Also, the coating exhibited high infrared emissivity related to high valance state (Pr4+) and oxygen vacancies. And the average infrared emissivity within 2–14 µm was 0.822 at 1300°C and presented slight decrease with the increase of temperature (the average infrared emissivity of 0.795 at 1800°C).

Highly bioactive hydroxyapatite coating made by flame spray technique

This research involves fabrication and characterization of flame sprayed hydroxyapatite (HA) coatings on 316 stainless steel substrates where the desirable structure with high porosity can be obtained. Nano-sized HA powder was synthesized and calcined at 600 °C. The subsequent powder was used as feedstock powder for flame spray technique (FS). In-flight particles of HA were spherical with the range of particle size between 3–37 µm. The average coating thickness was 128 µm and the crystalline phases were a mixture of HA and tricalcium phosphate (TCP). Simulated body fluid (SBF) test showed that HA layer was formed after 7 days. Highly bioactive properties were due to high surface area from rough coating and porous structure, which would be beneficial from the flame spray technique. The coating is promising for applications in biomedical field.

Microstructure and mechanical properties of the (Al1/6Cr1/6Nb1/6Ta1/6Ti1/3)O2 high-entropy ceramic coating prepared by laser cladding

The (Al1/6Cr1/6Nb1/6Ta1/6Ti1/3)O2 high-entropy ceramic coating was fabricated by laser cladding in this study. For the continue and dense coating structure, there were pre-treatments including the squash presetting of feedstock powders and the deposition of Al2O3-TiO2 coating on steel substrate by atmospheric plasma spray. The XRD technology was conducted for investigating the phase transitions during the fabrication of (Al1/6Cr1/6Nb1/6Ta1/6Ti1/3)O2 coating. The SEM, EDS technologies and nano-indenter were operated for evaluating the microstructure, composition and mechanical properties of the (Al1/6Cr1/6Nb1/6Ta1/6Ti1/3)O2 coating. The results showed that the feedstocks with various structures were successfully transformed into the (Al1/6Cr1/6Nb1/6Ta1/6Ti1/3)O2 high-entropy ceramic with rutile structure as well as the formation of intermediate products in similar structures. The (Al1/6Cr1/6Nb1/6Ta1/6Ti1/3)O2 coating had a tight combination with the Al2O3-TiO2 coating and showed a thick and compact structure, which included various dendritic crystal structures composed of segregated Al2O3. The (Al1/6Cr1/6Nb1/6Ta1/6Ti1/3)O2 coating exhibited a high level of hardness (13.58 ± 2.05 GPa) and elastic modulus (275.24 ± 32.26 GPa).

Flame Spray Pyrolysis Synthesis of Ultra-Small High-Entropy Alloy-Supported Oxide Nanoparticles for CO2 Hydrogenation Catalysts.

The synthesis of high-entropy alloys (HEAs) with ultra-small particle sizes has long been a challenging task. The complex and time-consuming synthesis process hinders their practical application and widespread adoption. This study presents the novel synthesis of TiO2 nanoparticles loaded with a quinary high-entropy alloy through flame spray pyrolysis (FSP) for the first time. The extremely fast heating rate of flame combustion makes the precursor fast pyrolysis gasification, high temperature in the flame field promotes the metal vapor mixing uniformly, and the fast quenching process can reduce the particle aggregation sintering, the ultra-small particle size of HEA firmly attached to the TiO2 surface. The catalysts prepared via this gas-to-particle pathway exhibit excellent performance in CO2 hydrogenation, achieving a conversion rate of 62% at 450°C, and maintaining their activity for over 220h without significant particle agglomeration. This finding provides valuable insights for the future design of catalytically active materials with enhanced activity and long-term stability.

Multiscale structural understanding of plasma spraying anti-ablation coating: an example of Ta-Hf-W-C ultrahigh temperature ceramics

The coating formation and structural design of ultra-high temperature ceramics (UHTCs) for aerospace vehicle anti-ablation coatings through plasma spraying remain uncertain despite extensive engineering applications. In this study, (Ta,Hf,W)C/HfC micro-composite, (Ta,Hf,W)C single-phase, and (Ta,Hf,C)/W nanocomposite coatings were successfully prepared using induction plasma spheroidization (IPS), vacuum plasma spraying (VPS), and spark plasma sintering (SPS). Density functional theory (DFT) was employed to capture the electronic structure of (Ta,Hf,W)Cy (y = 1, 0.875, 0.75, 0.5), confirming the influence of carbon vacancies and ceramic metallicity on the plastic forming behavior of sprayed coatings. Additionally, the contribution of HfC to structural stability and WC to the metallicity of carbon-based rock salt-structured UHTCs was elucidated. The pivotal role of carbon vacancies in inducing metastable phase formation and metal phase precipitation for (Ta,Hf,W)C was identified. Ablation behavior variations resulted from differences in multi-scale coating structures, where transverse cracks exhibited more detrimental effects than vertical cracks. Notably, a scale effect of oxidation related to the uniformity of metal elements in the multicomponent ceramic coating was uncovered. It was determined that components capable of forming high melting point oxides should not be uniformly dissolved in the matrix.

Failure mechanisms for Gd2O3–Yb2O3 co-doped YSZ thermal barrier coatings under high-temperature gradient

In this study, Gd2O3–Yb2O3 co-doped YSZ thermal barrier coatings with a top coat thickness of 400 μm were prepared on a nickel-based superalloy by atmospheric plasma spraying. The samples underwent multiple short-term and single long-term thermal exposures through burner rig tests under high-temperature gradients. The short-term thermal exposure duration of the coating was 25 s and the long-term thermal exposure duration was 1200 s. The microstructures and phase compositions of the samples were characterized, and their failure mechanism was discussed. The results demonstrate that during the burner rig tests, the coating surface temperature reached 2600K, resulting in coating sintering and sintered zone formation comprising coarse equiaxed grains. The short-term thermal exposure life of the coating is 3 cycles, and the long-term life is more than 1200s. After the single 1200s thermal exposure, the coating exhibited a stable cubic phase. However, under multiple 25s thermal exposures, the depth of the sintered zone increased with increasing number of cycles, leading to the formation of various vertical and transverse cracks within the coating. Coating failure was due to a combination of sintering and thermal-mismatch-induced stress.The early-stage coating delamination was attributed to sintering-induced transverse cracks, while the overall spallation was primarily ascribed to thermal-mismatch-induced transverse cracks.

Preparation of Bi4Ti3O12/TiO2 by flame spray pyrolysis for photoelectrocatalytic degradation of tetracycline

The negative effects of the irrational use of antibiotics have been increasing attention from the public, making it urgently needed to develop effective techniques for removing antibiotics from wastewater. Simultaneously, the construction of heterogeneous TiO2 photoanodes can be used to enhance photoelectrocatalytic performance. Herein, we used an advanced method, namely one-step flame spray pyrolysis (FSP) to in-situ prepare Bi4Ti3O12/TiO2 heterostructures. The ultra-high temperature characteristics of this method facilitated the high dispersion of Bi species on TiO2, leading to the formation of the Bi4Ti3O12 phase within milliseconds. Bi4Ti3O12 forms a “Z" type heterojunction with TiO2, improving charge separation and enhancing electron transfer efficiency. The photoeletrocatalytic degradation effect of Bi4Ti3O12/TiO2 on tetracycline is significantly improved. Under simulated sunlight irradiation for 75 min and 1V voltage, the removal of tetracycline can reach 99.7%. The recycling degradation experiments demonstrated the remarkable reusability and stability of Bi4Ti3O12/TiO2, while the evaluation of degradation intermediates and toxicity analysis of tetracycline were also conducted. Furthermore, free radical trapping experiments confirmed that hydroxyl radicals and holes play a significant role in the removal of tetracycline.

Al2O3 Coatings for Protection of Stainless Steel 316L against Corrosion in Zn-Al and Zn-Al-Mg

The production and quality of automotive-grade galvanised steel are affected by the limited service life of the pot roll bearings used in continuous galvanising lines. The journal bearings are subjected to severe degradation as they react with the molten Zn bath, and coatings can provide corrosion protection to the bearing materials. This research investigates the performance of Al2O3 coatings applied via the HVOF thermal spray process to stainless steel 316L substrates. Immersion tests were conducted in baths of different compositions, namely GI (Zn-0.3 wt.% Al) and ZMA (Zn-1.5 wt.% Al-1.5 wt.% Mg). Material characterisation after testing showed evidence of coating degradation after 1 week, as the coating tended to crack and detach from the substrate, allowing the molten Zn to attack the underlying steel. The coefficient of thermal expansion of Al2O3 and steel was measured, and a difference of 13 × 10−6 K−1 was found, leading to the development of cracks in the coatings. Zn penetration through cracks was determined to be the main failure mechanism of the Al2O3 coatings, which otherwise remained inert to Zn-Al. Conversely, the coatings immersed in Zn-Al-Mg reacted with the Mg in the molten metal bath, showing that changing bath composition affected the performance of the coatings in molten Zn alloy.

The improvement of wear and corrosion resistance of nickel-graphite coating with modified graphite phase size

The corrosion resistance, friction and wear properties of an abradable seal coating are highly dependent on the size and distribution of lubrication phase. In this work, nickel-graphite (Ni-G) coatings were fabricated by a supersonic atmospheric plasma spraying system (SAPS) and a standard atmospheric plasma spraying system (APS), respectively. The effect of size and distribution of graphite phase on the performance of Ni-G coatings was investigated. The results suggested that the SAPS coating had an average single graphite phase area of 35.4 ± 5.1 μm2, which is approximately 35.4 % less than that of the APS coating, while the average graphite phase width and length in SAPS coating decreased by 22.2 % and 16.7 % compared to the APS coating. The fine distributed graphite phase improved the formation of structure with a small cathode and a large anode, which effectively increased the corrosion resistance of SAPS coating. The reciprocating sliding friction facilitated the creation of a uniform and uninterrupted lubricant layer, attributed to the finely dispersed graphite phase of SAPS coating. In comparison to the as-sprayed and subsequent corroded APS coatings, the friction coefficients of the SAPS coating exhibited a reduction of approximately 9.1 % and 13.3 %, respectively. The aforementioned findings showed that the small-sized graphite phase was conductive to the improvement of corrosion resistance, friction and wear properties of Ni-G abradable coatings.

Corrosion Behavior of Al2O3-40TiO2 Coating Deposited on 20MnNiMo Steel via Atmospheric Plasma Spraying in Hydrogen Sulfide Seawater Stress Environments

In this study, an Al2O3-40TiO2 coating was deposited on 20MnNiMo steel via atmospheric plasma spraying. The corrosion behavior of the coating was investigated in both artificial seawater and a simulated environment with hydrogen sulfide and high pressure. Additionally, ion dissolution experiments were conducted to evaluate the coating’s bio-friendliness. In artificial seawater, the corrosion rate (based on the corrosion current) of the Al2O3-40TiO2 coating initially decreased before increasing. It was speculated that the blocking of corrosion products in the defect channels was helpful in delaying the progress of corrosion in the early stage. The coating had a corrosion current on the order of 10−6 A/cm2 in artificial seawater, suggesting good protection in conventional seawater environments. In the simulated environment, the corrosion rate (based on the weight loss) of the Al2O3-40TiO2 coating showed a continuously declining trend. It was deduced that, unlike corrosion products in artificial seawater, the corrosion products in the simulated environment (e.g., metal sulfide) might be more chemically stable, leading to a longer blocking effect. Therefore, a minimal corrosion rate of 0.0030 mm/a was obtained after the coating was immersed for 30 days. The amount of dissolved coated elements was negligible and there were only small amounts of dissolved non-coated elements such as Ni and Mo. The developed coating can be considered to be highly biofriendly if the non-coated area of the specimen is well sealed.

Application of MgO/ZrO2 coating on 309 stainless steel to increase resistance to corrosion at high temperatures and oxidation by an electrochemical method

Abstract 309 stainless steel is one of the steels that have the highest resistance to corrosion and thermal oxidation compared to other steel grades, but it should not be used at temperatures higher than 980°C if there are temperature fluctuations. Additionally, 309 stainless steel is not designed for use in wet environments and has the least corrosion resistance. This study aims to cover 309 stainless steel with MgO/ZrO2 particles using a two-step electroplating deposition method and then sintering to increase its resistance to wet corrosion and oxidation in temperature fluctuations. The intermediate ZrO2 coating makes the outer MgO layer about two times thicker and reduces the corrosion current density. The morphology of the coatings was determined using scanning electron microscopy and X-ray diffraction, and oxidation resistance was determined using cyclic oxidation tests and the wet corrosion test of the corrosion solution. 3.5% NaCl was used. The results showed that the coated samples, due to the use of TiO2 middle layer and MgO protective layer in the electrochemical method, have a 2-fold increase in wet corrosion and an increase in hardness of about 77%, as well as an increase in oxidation resistance of 1.8% compared to the sample without coating. Also, the reason for using the electrochemical deposition method is for better surface smoothness and less porosity of the coating as well as its use on all metals compared to thermal spray methods.

Development of thermal barrier coating on single crystal superalloy CMSX-4 by two-source evaporation EB-PVD and hot corrosion performance of the coating in a simulated aero-engine environment

Superalloys are crucial in high-temperature applications, particularly in the gas turbine industries. With the development of high-temperature superalloy materials, efforts are still being made to improve the turbine entry temperature (TET), which will ultimately raise the efficiency of gas turbines. In this research, a second-generation single-crystal superalloy CMSX-4 based on nickel was prepared. The surface was coated by thermal barrier coating (TBC) with a bond coat of NiCoCrAlY with vacuum plasma spray (VPS) and a top coat with Yttria Stabilized Zirconia (YSZ) by Electron Beam Physical Vapor Deposition (EB-PVD) with a minimal current of 2.3 A with two sources compared to the conventional high-current that has been currently employed. These CMSX-4 specimens, both the as-cast and TBC coated, were used to test the effects of cyclic oxidation and hot corrosion at 1000 °C, simulating an aircraft engine. Also, a hot corrosion test using salt compositions (Wt%) of 60Na2SO4 - 40NaCl was performed simulating an aviation engine environmental condition. A FE-SEM/EDS analysis was used to examine the surface and cross-section microstructures of oxidized, hot-corroded as-cast, and hot-corroded TBC-coated CMSX-4 and its corrosion products. Using the XRD technique, the phases that were found in the oxidized and hot-corroded samples were identified. The outcome demonstrated that the EB-PVD TBC-coating on CMSX-4 with beam switching technique and a lower electron beam current has adequate protection without any damage to the coatings at 1000 °C.

Preparation, characterization, and photocatalytic performance of atmospheric plasma-sprayed TiO2/Al2O3 coatings on glass substrates

Conventional methods for wastewater treatment are not always efficient in persistent organic pollutant degradation processes. Therefore, low-cost and effective methods of their removal from sewage are constantly sought. This study presents an attempt to fabricate thermally sprayed ceramic coatings on glass and their characterization. Granulation of TiO2, Al2O3, and their blends in different mass ratios was done. Assessment of actual density and specific surface area was performed, and TiO2, Al2O3, and TiO2/Al2O3 were then used as a coating material for the deposition on glass substrates in atmospheric plasma spraying. Surface analysis of coatings was done by evaluating their roughness and wettability. Both powder and coatings samples were characterized using the X-ray diffraction method and scanning electron microscopy. The photocatalytic activity was estimated in the Eosin Y degradation process under UV light. UV–Vis spectroscopy was applied to observe the changes in the dye concentration. Additional tests for color measurements before and after photodegradation were carried out using a sphere spectrophotometer in CIELab color space. Particle size distribution was examined for the powder samples after the granulation and d50 was stated at 48.42–63.28 µm. Characterization of coatings via roughness measurements showed the average roughness of a surface equal to 4.90–9.65 µm. Moreover, most of the coatings appeared to be hydrophobic with water contact angles between 100° and 130°. All of the coatings showed Eosin Y degradation ability and the highest efficiency was reached for 100T/C, A75T/C, and A50T/C samples and stated at 71%, 62%, and 51%, respectively.Graphical abstract

Bimodal nanomechanical performance of nanostructured Lu2Si2O7 environmental barrier coating

Lutetium disilicate (Lu2Si2O7) is considered a promising material for environmental barrier coatings because of its remarkable high-temperature stability and low thermal conductivity. In this study, nanostructured Lu2Si2O7 coating was prepared successfully using as-prepared feedstocks via atmospheric plasma spraying. The nanomechanical performance of the coating was studied. The results showed that the coating exhibited a bimodal nanomechanical performance attributed to the bimodal distribution of its microstructure; i.e., in the coating, the melted lamella exhibited higher elastic modulus and nanohardness, whereas the unmelted and semi-melted parts processed low elastic modulus and nanohardness. The elastic modulus and nanohardness of the coating were 143.438 ± 25.449 GPa and 9.239 ± 3.514 GPa, respectively. Furthermore, the elastic and plastic works were 9.018–14.752 nJ and 12.792–25.793 nJ, respectively. The average value of the microhardness dissipation parameter of the coating was 0.615, demonstrated that the remarkable wear resistance of the coating.

Corrosion behaviors of single-layer and double-layer nickel alloy coatings fabricated by arc spraying and high-velocity oxy-fuel

This study investigates single-layer and double-layer thermally sprayed nickel alloy coatings (bond and top coatings). Ni-5 wt% Al and Ni-20 wt% Cr were used as bond coatings, whereas highly alloyed Ni-based coatings, Hastelloy C276 or Inconel 625 were used as top coatings. Arc spraying (A) and high-velocity oxy-fuel (HVOF) techniques were used to create the coatings on a 304 stainless steel substrate. The samples were studied by performing potentiodynamic polarization tests in a 20 vol% H2SO4 solution at room temperature. The scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) and wavelength dispersive X-ray spectroscopy (WDS) techniques were used to investigate the microstructure and chemical composition of the coatings. The arc sprayed coatings are composed of a lamellar microstructure with low porosities, unmelted particles, and high oxides at the intersplats. A uniform and compact coating with minimal oxides and porosity was achieved for all coatings via HVOF technique. In single-layer coatings, arc spray coating surpasses HVOF coating owing to its oxide layers, which impede sulfuric solution penetration and bolster resistance against electrolyte infiltration. Double-layer coatings, comprising a bonding layer and a top coating, using the same thermal spray method have shown to enhance corrosion resistance.

REVIEW: MATERIALS FOR IMPREGNATION OF POROUS METALLIZATION THERMAL SPRAYED ANTICORROSIVE COATINGS OF SUBMERSIBLEOILFIELD EQUIPMENT. Part 1

Submersible oilfield equipment undergoes aggressive corrosive effects of petroleum fluid, abrasive effects of mechanical impurities during operation, and also operates at elevated temperatures in the bottom. The most effective way to protect the outer surface of oilfield equipment is the use of metallization thermal sprayed coatings, and therefore the application of thermal spraying technology is becoming more and more in demand.However, the formation of a coating structure from many particles of molten material, due to their spraying, incomplete melting and loose packaging, leads to the formation of porosity, and porosity is one of the main disadvantages of thermal sprayed coatings. To eliminate this disadvantage, it is possible to use impregnation of porous coatings with various compositions, in which case the coating becomes composite. Depending on the operating environment, temperature conditions and operating conditions, metal, organic and inorganic impregnating compositions are used,but their use in the oil environment has been little studied, therefore the development of composite impregnated coatings is relevant for the protection of submersible oilfield equipment. The article highlights the influence of technological modes of its application on the porosity of thermal sprayed coating and the quality of substrate surface preparation. The main methods of sealing the porosity of thermal sprayed coatings by impregnation are described. The mechanism of impregnation (infiltration) of porous coatings, used methods of application and their classification are described, the determining role of wetting the coating with an impregnating material is emphasized. The effect of the rough surface of a thermal sprayed coating is shown, which consists in enhancing the wetting properties of the impregnating composition, the influence of roughness on the formation of adhesive bonds between the coating and the impregnating composition.The review presents traditional impregnating materials used in industry and their application modes.The application of metal and non-polymer inorganic impregnating compounds, represented mainly by salts of inorganic acids (nitrates, phosphates, silicates), is described. Specific test results are presented, including for the corrosion and abrasive resistance of thermal sprayed coatings after the application of impregnating compounds.