This paper proposes a new procedure for preparing enameled steels by thermal spraying the ceramic enamel followed by laser sintering and vitrification to obtain a smooth, corrosion-resistant, and anti-fouling coating. This study investigated the influence of enamel formulation, spraying methods, and laser parameters on the coating properties and characteristics, including microstructure, topography, phase composition, mechanical stability, and laser vitrification.

Cold spraying mixed metal-ceramic powders creates metallic matrix composites, but typically achieves low hard phase content in deposits. We investigated this challenge using various hard phases (SiC, diamond, WC, W) with Al and Cu metal matrices. Our results reveal that density difference—not hardness—between components primarily determines deposition efficiency. When using Al with similarly dense materials (diamond, SiC), deposit compositions remained comparable despite hardness variations. However, mixing Al with 50 vol.% of WC or W produced deposits containing 57.9 vol.% and 79.8 vol.% hard phases, respectively. Based on these findings, we established a ballistic theory-based criterion for effective hard particle deposition.

The effect of martensitic phase transformation on cavitation erosion resistance for a deposited layer prepared from a Fe-8Cr- C-1.5Al-Ti flux-cored wire of metastable steel was studied. A reference material of AISI 316L stainless steel was used as a substrate. Cavitation tests were performed using a modified ultrasonic tester. X-ray diffraction was used to examine the phase transformation before and after cavitation tests. Also, the eroded surfaces of specimens were investigated by optical microscope (OM), scanning electron microscope (SEM), and 3D optical profilometer. The cavitation results revealed that the deposited layer exhibited a resistance to cavitation erosion approximately 10 times higher than the AISI 316L steel due to the martensitic phase transformation occurring during the cavitation process. The phase transformation plays a main role to minimize the cavitation damage of specimen. This is due to the fact that it contributes to obstructing movement of dislocations and increasing the hardness as a result of the increased hardening on the surface.

Binary spinel-type metal oxides (AB 2 O 4 ) semiconductors, including ferrites (AFe 2 O 4 ), are attractive photocatalysts thanks to their excellent visible light response and good photochemical activity and stability for the photodegradation of organic pollutants. Currently, their synthesis proceeds via conventional chemical routes that follow rather tedious protocols and the final preparations consist in nano-powders, a form that is not exempt of EHS (Environment, health and safety) risks along their handling. From an industry perspective, it is desirable to dispose of an efficient and preferably simple synthesis route capable to produce photocatalytic preparations in a non-dispersible form, for instance in the form of robust films attached on solid substrates. We report herein a single-step method based on the Solution Precursor Plasma Spray (SPPS) process that enables the preparation of promisingly active ferrite-based photocatalytic films, namely CuFe 2 O 4 and ZnFe 2 O 4 . We have investigated various types of precursor solutions, including the atomic A/Fe ratios, solvent type and solute concentration, and studied the evolution of the phase composition of the resultant CuFe 2 O 4 and ZnFe 2 O 4 films by XRD. The corresponding surface morphologies and energy bandgaps were also studied by SEM and UV-Vis spectroscopy, respectively. Then the photocatalytic activities of the selective ferrite films were evaluated through the degradation of aqueous solutions of the Orange II dye under different light irradiations. The results of the overall work also revealed that SPPS process represents a fast, one-step, versatile alternative compared to conventional multi-step processes, which is suitable for preparing complex composition metal oxide film-formed photocatalyst.

The powder of HSS (HSS23, AISI M3:2) was deposited by pulsed-PTA method on to low alloyed steel substrate. The influence of pulsation frequency was evaluated on the surface of deposits and on their cross sections by both light microscope and by Vickers hardness measurement apparatus and extreme properties mapping (XPS). Surfacing parameters at current frequency from 0 to 200Hz were tested during deposition of single weld bead. Dilution and heat affected zone were evaluated and compared for all tested parameters. The presence of retained austenite after deposition was determined by X-ray diffraction. The beads deposited with different frequencies differ in their shape, dilution degree, microhardness and penetration depth. It was found that the microhardness increases with current frequency.

This study assesses the viability of three suspension spray processes for producing photocatalytic TiO 2 . In the experiments, flame, plasma, and HVOF torches were used to spray TiO 2 suspensions onto stainless steel substrates, varying process parameters in order to gauge their effect on phase composition, crystal size and, in turn, photoactivity. The TiO 2 samples were characterized by means of XRD, SEM, and UV-Vis analysis and photocatalytic hydrogen-production testing. Suspension flame spraying proved to be the most effective method, producing phase-controlled nanostructured titania 32% more photoactive than the SPS samples and up to five times more active than analogous coatings produced by CVD.

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.

High-Sn bearing alloys have been used for more than a century in many areas of industry. They are typically applied by casting, although thermal spraying is gaining in use, particularly for component repairs. This study evaluates the effects of HVOF spray parameters on the velocity, temperature, size, and trajectory of Babbitt particles and correlates the in-flight characteristics with coating porosity and intermetallic phase distribution. In the experiments, Babbitt layers up to 370 μm thick were deposited on carbon steel substrates while measuring particle properties and deposition efficiency. Coating samples were analyzed by means of optical and electronic microscopy and some were chemically etched to reveal the size and distribution of intermetallic phases. Test results show a significant refinement in intermetallic phase distribution when compared with commercial flame and arc-sprayed coatings.

High-entropy alloys (HEAs) are well suited for use in high-temperature environments due to their combination of strength, ductility, thermal stability, and corrosion and wear resistance. In this study, NiCoCrAlSi-based HEA coatings are deposited by HVOF and air plasma spraying (APS) and their phases, microstructure, and composition are evaluated by means of XRD, SEM, and EDS analysis. The results show that BCC/B2 phases are the main constituent in HVOF coatings that were diffusion heat treated. APS coatings of the same composition, on the other hand, exhibited a two-phase structure consisting of L12 and BCC/B2 phases. The HEA coatings produced by HVOF were tested for oxidation resistance and their morphology and oxide scales were examined with the aim of developing a high-quality bond coat for thermal barrier coating (TBC) systems.

In this study, WC-Co coatings with nano-sized TiC additions were deposited on steel substrates by high velocity air fuel (HVAF) spraying and their microstructure and phase composition was analyzed using different electron microscopy techniques. Tungsten-reinforced cobalt phases detected in the vicinity of WC grains were identified as Co 0.9 W 0.1 by selected area diffraction. No titanium phases other than TiC were found, which suggests that nano-TiC may increase the stability of metallic matrix microstructure in WC-based coatings.

Previous studies have shown that austenite-to-martensite transformations occur in certain ferrous materials under an applied load, along with synergistic improvements in hardness and wear resistance. The aim of this study is to investigate the effects of such transformations on the tribological properties of chromium steel (FeCCrTiAl) coatings and overlays. The coatings were produced by arc wire spraying and the overlays by arc surfacing. Microstructure and phase composition were analyzed and abrasive and adhesive wear tests were conducted. Strain-induced nucleation of martensite under external load was confirmed by structural changes and differences in the tribological properties of the coatings and overlays were attributed to the particular conditions of their formation.

This work investigates the sliding wear resistance of alumina coatings deposited on stainless steel substrates by HVOF and air plasma spraying, using fine (1-5 μm) and conventional (10-45 μm) powders. Sliding wear tests were carried out using a sintered WC-Co ball as the counter-body and the wear tracks were examined to obtain a better understanding of wear mechanisms. HVOF coatings showed an order of magnitude improvement in wear resistance compared to their APS counterparts. The disparity in wear performance is correlated to differences in phase composition, porosity, hardness, and fracture toughness as revealed by SEM and XRD analysis and nanoindentation testing. The development of tribofilms and their role in wear behavior is also discussed.

This study deals with the deposition of coating materials that can be difficult to process by plasma spraying, including lanthanum and gadolinium zirconate, two pyrochlores of interest for thermal barrier applications, and lanthanum strontium cobalt ferrite (LSCF), a perovskite of interest for gas separation membranes. In addition to conventional atmospheric plasma spraying (APS), the feedstock powders were applied by suspension plasma spraying (SPS) and plasma spray-physical vapor deposition (PS-PVD). The spraying processes are described in detail along with the characteristics of the powders and coatings and the effects of various spray parameters on splat behavior and coating composition and structure.

This study evaluates the effects of heat treating on the microstructure, phase composition, and friction and wear behavior of plasma sprayed FeAl coatings. Fe-40Al feedstock powder was deposited on mild steel substrates by atmospheric plasma spraying and the coatings were vacuum annealed at 500, 650, 900, and 1000 °C. An examination of coating cross-sections revealed the presence of diffusion layers in the samples treated at 900 and 1000 °C. XRD analysis indicates that annealing at 650°C facilitates the transformation of Fe(Al) solid solution into FeAl intermetallic phase, resulting in an increase in coating hardness. At higher temperatures, however, Al depletion occurs along with a reduction in hardness. Tribological testing showed that both the friction coefficient and the effects of wear increased after heat treatment.

This study assesses the potential use of thermally sprayed dicalcium diiron pentaoxide (Ca 2 Fe 2 O 5 ) for thermoelectric generators. Ca 2 Fe 2 O 5 coatings up to 2 mm thick were produced by atmospheric plasma spraying and examined. Compared to the bulk material, the coatings exhibit lower thermal and electrical conductivity. The Seebeck coefficient could not be measured, and the thermoelectric performance was inadequate. The limitations derive not only from the thermal spray process, but also the material itself.

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, gas- and water-stabilized plasma torches were used to spray cesium-doped yttrium aluminum garnet (Ce:YAG) on different substrate materials and in large-area free-standing layers. The coatings were evaluated based on microstructure, crystallinity, and thermal stability, and tests were performed to measure porosity, hardness, phase composition, band-gap energy, and the presence of defects. Some coatings were also heat treated to determine how it changes their spectral response. The results of the examinations and tests are presented in the paper.

This work demonstrates a new single-cathode, multi-anode plasma spray process and compares it with conventional APS and HVOF spraying. Alumina feedstock powders mixed with 13, 40, and 44 wt% titania were deposited under a wide range of spraying conditions following a design of experiments approach. Deposition rate and efficiency were measured and coating characteristics, including microstructure, phase composition, hardness, Young’s modulus, electrical resistivity, and cavitation wear, are compared. The results are presented and the advantages of each process are discussed.

A comparative study was done on the structure and tribological properties of arc sprayed coatings and arc surfaced layers of TRIP steel. An iron alloy feedstock was used due to its ability to form a metastable austenite structure in both sprayed and surfaced layers that can be transformed to hard martensite by an applied external load. Microstructural and phase analysis and adhesive and abrasive wear tests were conducted to evaluate the coatings and surfaced layers. Differences in properties are explained based on input energy parameters.

Thick Fe-Al deposits were produced by low-pressure cold spraying using heated air as the working gas. The coatings were isothermally annealed for two hours in Ar at temperatures from 250 °C to 750 °C. Changes in fracture behavior and microhardness were evaluated along with the microstructure and composition of newly formed phases. The results show that the evolution of intermetallic phases was driven by diffusion at temperatures above 550 °C. The new phases formed a hard skeleton that preserved the general shape of the samples during treatment despite the growth of external dimensions and porosity.