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Yttria-stabilized zirconia (YSZ) coatings are widely utilized thermal protective layers for metal and superalloy surfaces. These coatings are employed as thermal barrier coating (TBCs) to insulate metallic parts from higher thermal energy, thereby minimizing the cooling need for the topcoat ceramic layer. The choice of material is 7 wt% YSZ due to its exceptional capability to withstand challenging conditions characterized by extremely high temperatures and pressures, typically employed by the atmospheric plasma spraying (APS) in gas turbines, effectively extending their lifespan and improving performance. The deposition process of TBCs is significantly influenced by various spraying parameters, including gas flow rate and current (amp). These key parameters mutually play a significant role in controlling thermal stability, phase composition, and improved mechanical and microstructure properties. The aim of this research is to evaluate and contrast the impact of various spraying parameters on YSZ TBC performance. Accordingly, the influence of Hydrogen (H 2), Argon (Ar) flow rate, and Current (amp) was investigated. Microstructure and elemental mapping studying was conducted using Field Emission Scanning Electron Microscopy FESEM/EDS and phase studying was examined with X-ray diffraction (XRD). Porosity was measured by IMAGE J software while hardness measurement was calculated by Vickers hardness tester. Additionally, thermal cycling tests were conducted between 700 °C and 1200 °C. The porous coatings exhibited poor performance, delaminating early during the tests. In contrast, dense coatings performed significantly better, enduring up to 140 cycles before failure. [ABSTRACT FROM AUTHOR]

The capacity to endure harsh wear in demanding conditions in stainless steel drops under extreme nature and applications. Protecting the surface by providing a coating layer supports the usage in harsh conditions. In this work, SS316L is coated with AlCoCrFeNi high-entropy alloy (HEA) by atmospheric plasma spray process and annealed at 600°C for 2 hours. The AlCoCrFeNi HEA exhibited spherical particles with bcc phase and 20 µm particle size. The coating morphology revealed a uniform coating with a homogeneous distribution of HEA particles over a thickness of 150 µm. The coating post-annealing offered improved microhardness by 12% than the coated sample before annealing. The wear test was executed by varying load, sliding distance, and sliding velocity at normal temperature, 400°C and 600°C and the corresponding worn surface was analysed. The coated samples after annealing showed 57.6%, 87.5%, and 65.4% improved wear resistance at normal temperature than the coated sample before annealing at minimum levels of load, sliding velocity and distance. The wear rate of coated and annealed samples revealed 5.2%, 4.5%, and 4.4% better wear resistance at 400°C than the coated samples before annealing. The worn surface morphology showcased wear mechanisms to be delamination, abrasive wear, and oxide layer formation under all conditions. IMPACT STATEMENT: The present work reports a novel study of plasma spraying of SS316L substrate using AlCoCrFeNi High-Entropy Alloy that marks the first attempt in analysing its hot wear performance. [ABSTRACT FROM AUTHOR]

The performance of the Al0.5CoCrFeNi2Ti HEA atmospheric plasma-sprayed coating was extended from characterizing the properties of its powder prepared via the gas atomization method. It was observed that the gas-atomized HEA powders possessed a solid solution BCC phase, while a major phase transformation to a FCC-L21 intermetallic phase occurred during the annealing process. The formation of the intermetallic phase resulted in an increase in average hardness from 6.28 to 7.64 GPa after annealing at 900 °C for 1 h. Afterward, HEA powders were applied in the atmospheric plasma spray technology. The phase constitution of Al0.5CoCrFeNi2Ti HEA coatings was investigated by varying powder size and applied current. It was observed that the smaller powder sizes prone to oxidation, whereas higher applied current facilitated the phase transformation from BCC to FCC phase. The nanoindentation test indicated distinct average microhardness values for the interlamellar oxide region, BCC unmelted particle and FCC phase lamellar region, which was measured at 12.35, 8.68 and 5.97 GPa, respectively. As a result, the adjustability of coating hardness was achieved by manipulating the relative phase ratio. [ABSTRACT FROM AUTHOR]

This work presents a multi-scale one-way-coupled thermo-mechanical method to determine the residual stress in an Atmospheric Plasma Spray (APS) process. The model uses three submodelling scale levels that range from the entire component (macroscopic) to a splat coating layer (microscopic) dimension. The three-level scale temperature and stress evolutions of an Al2O3 coating material on a flat aluminium substrate were analysed. The quenching stress for different substrate preheating temperatures up to 600 K at the end of the APS coating process was discussed and validated through an experimental in situ curvature method and Stoney's quenching stress equation. [ABSTRACT FROM AUTHOR]

To investigate the effect of the spraying process parameters on the properties of NiCoCrAlYTa-Cr2O3-Cu-Mo high-temperature wear-resistant coating， the coating is prepared by atmospheric plasma spray （APS） process based on the orthogonal experiment. The range analysis method is used to study the primary and secondary relationships of the process parameters on the microstructure， hardness， and bonding strength of the NiCoCrAlYTa-Cr2O3-Cu-Mo coating， and the spraying process parameters are optimized. The optimized process parameters are that the argon flow rate is 50 L/min， the hydrogen flow rate is 12 L/min， the current is 500 A， and the spraying distance is 100 mm. With the optimized spraying process parameters， the microstructure of the coating is very dense， the porosity is lower than 1%， and the average bonding strength， hardness， and average oxidation speed during 50-100 h at 900 ℃ are 70.7 MPa， 543.7 HV， and 0.07302 g/（m2·h）， respectively. In addition， the friction coefficient and wear rate of NiCoCrAlYTa-Cr2O3-Cu-Mo coating are 0.248 and 2.12×10-6 mm3/（N·m） at 800 ℃， exhibiting good friction and wear properties.

Abstract Surfaces are commonly enhanced with wear-resistant coatings to improve their resistance to abrasion, erosion, and other forms of wear. These coatings play a crucial role in extending the lifespan and improving the performance of materials and components exposed to challenging conditions. The objective of the current study is to deposit thermally sprayed 3-layer TiC–12Co–10ZrO2/NiCoCrAlMo functionally graded coatings on SS410 substrates using atmospheric plasma spray. The results revealed that by employing appropriate ceramic proportions, the microhardness of graded coatings increased to 990.4 HV, which is approximately 3.21 times higher than that of the substrate. Furthermore, the tribological properties of graded coating exhibited superior resistance compared to the substrate, where process settings were varied. Specifically, graded coating samples subjected to the applied load, sliding distance, and sliding velocity showed improved wear resistance of 78.51%, 68.42%, and 76.66% respectively in extreme conditions compared with uncoated samples. The characterization of the worn surface revealed a sequential occurrence of wear mechanisms: abrasive, adhesive, and delamination. The formation of TiO2 and Cr2O3 tribo-oxide film protects the surface against the wear mechanism and is applicable in extreme wear environments.

This paper introduces novel possibilities of using recently developed high-power lasers for high-speed surface periodic structuring/patterning of the ceramic substrates for the subsequent thermal spray coating deposition, which may be difficult to pattern using conventional methods. Yttria-stabilized zirconia (YSZ) was selected as model ceramic for both substrates and coating. Three different types of patterns were produced by three different laser technologies: dimples with nominal depth of 15 and 30 µm (pulsed nanosecond laser), grids with nominal depth of 15 and 30 µm (continuous wave laser), and pillars with nominal depth 30 µm (ultrashort pulsed femtosecond laser). All surface patterns were thoroughly periodical and their surface roughness ranged from Sa = 4.5 to 10.3 µm, significantly surpassing conventional grit-blasting. Pulsed and continuous wave lasers showed very high process rates (up to 54.5 mm2/s and 323.6 mm2/s, respectively) and tendency to develop network of shallow surface cracks. Ultrashort pulsed laser technology was slower (process rate 1.65 mm2/s) but the surface was crack-free with desirable miniature anchoring points. Plasma spraying was carried out with powder, solution, and suspension feedstocks providing an experimental matrix demonstrating potential benefits and risks of each pattern-feedstock combination. Not all combinations led to successful coating deposition, but results show that microstructure of the coating may be deliberately controlled by laser texturing, in particular periodic substrate pattern led to periodic coating microstructure in the case of suspension spraying. Also adhesion/cohesion of the coating to the substrate may be in many cases significantly improved by laser patterning of the substrate. The highest coating adhesion/cohesion strength (26.2 ± 4.8 MPa) was achieved for the coating deposited from solution on pillar patterns. Finally, a possibility to combine the high-speed and advanced surface morphology produced by continuous wave and femtosecond lasers, respectively, and direct patterning of plasma sprayed coating were also demonstrated. [ABSTRACT FROM AUTHOR]

Thermal 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). [ABSTRACT FROM AUTHOR]

Present investigation attempted to explore the tribological properties of atmospheric plasma sprayed coatings. In order to assess the role of solid lubricants, different weight percentages (5, 10, and 15 wt.%) of silver (Ag) were taken, whilst MoS2 concentration remained fixed. Dry sliding wear tests were conducted for different specimens namely, Ni-Al-MoS2-5 wt.% Ag (NA5), Ni-Al-MoS2-10 wt.% Ag (NA10) and Ni-Al-MoS2-15 wt.% Ag (NA15) at different loads of 4, 9, 14 & 19 N, and slid speed of 0.3 m/s under room temperature (RT) conditions. It was observed that coefficient of friction (COF) and wear rate of specimens decreased as the load increased till 14 N, and beyond that increasing trend was noticed. However, the NA10 specimen has revealed the best tribological properties in terms of minimum COF (0.48) and wear rate (4.7 × 10−5 mm3/Nm) at 14 N and 0.3 m/s. The synergy of Ag and MoS2 on the frictional properties of specimens have been well explained with the help of worn surface morphologies and some useful conclusions were made. [ABSTRACT FROM AUTHOR]

A pure molybdenum (Mo) coating layer was manufactured by using the atmospheric plasma spray (APS) process and its wear and corrosion characteristics were investigated in this study. A Mo coating layer was prepared to a thickness of approximately 480 μm, and it had sound physical properties with a porosity of 2.9% and hardness of 434 Hv. Room temperature dry wear characteristics were measured through a ball-on-disk test under load conditions of 5 N, 10 N and 15 N. Based on the coefficient of friction graph at 5 N and 10 N, the oxides formed during wear functioned as a wear lubricant, thereby confirming an increase in wear resistance. However, at 15 N, wear behavior changed, and wear occurred due to splat pulling out. A potentiodynamic polarization test was conducted under an artificial seawater atmosphere, and Ecorr and Icorr measured 0.717 V and 7.2E-5 A/cm2, respectively. Corrosion mainly occurred at the splat boundary and pores that were present in the initial state. Based on the findings above, the potential application of APS Mo coating material was also discussed.

The novel application of laser surface texture as a method for enhancing the deposition of coatings on substrates has garnered significant interest. This study focuses on the use of atmospheric plasma-sprayed Mo–NiCrBSiCFe coating, which was applied to both laser surface textured and grit-blasted AISI 304 substrates. The coating powder was created by mechanically milling a mixture of 25 % molybdenum and 75 % NiCrBSiCFe powders, providing a unique combination of materials for the deposition coating. The analysis zeroed in on examining the effects of laser texture grooves on the microstructure, porosity, microhardness, and adhesion strength of the composite coating. The findings revealed that the composite coating primarily comprises MoO2, Mo, and Ni phases. In comparison to the grit-blasted substrate, the coating applied on the laser-textured groove substrate exhibited a porosity increase of 15.15 %, a pore size rise of 17.45 %, a notable 45.62 % improvement in adhesion strength, and a significant 23.57 % enhancement in scratch resistance. Furthermore, the coating on the laser-textured substrate exhibited fewer closed pores. The microhardness of the coating surface was higher than that of the coating cross-section within the grooves. Notably, the laser surface texture had a significant impact on the adhesion strength, microstructure, and hardness of the composite coating, surpassing the results achieved through traditional grit blasting. One novel observation from this study is that laser surface texturing can have a significant impact on the porosity of Mo–NiCrBSiCFe coatings. Another noteworthy finding is that laser surface texturing can enhance the hardness of Mo–NiCrBSiCFe coatings.

This study prepared the 7YSZ ceramic coatings based on AlCoCrFeNi bond coating by APS and PS-PVD methods, respectively. Two AlCoCrFeNi/7YSZ thermal barrier coating systems with different microstructures of ceramic coatings were obtained, and oxidation experiments at 1000 °C and 1100 °C were carried out for the two thermal barrier coating systems. The results showed that the AlCoCrFeNi/7YSZ(PS-PVD) thermal barrier coating system exhibits superior oxidation resistance compared to the AlCoCrFeNi/7YSZ(APS) thermal barrier coating system at 1000 °C and 1100 °C, which was attributed to the ceramic coating with a unique feather-columnar structure prepared by PS-PVD. Both thermal barrier coatings in this study produced a continuous and dense TGO layer composed of Al 2 O 3 after oxidation experiments. The oxidation rate constants k p of this study's two thermal barrier coatings were lower than the selected MCrAlY/YSZ thermal barrier coating systems under the same experimental conditions. It indicates that the AlCoCrFeNi bond coating exhibited excellent oxidation resistance and possesses the potential to be a new type of bond coating material. [ABSTRACT FROM AUTHOR]

Materials with enhanced wear resistance are constantly in high demand. Nickel-based self-fluxing materials deposited by atmospheric plasma spraying (APS) have feasible wear resistance performance. This study aimed to evaluate the results of a nickel-based self-fluxing alloy coating deposited on AISI 4340 steel substrate using APS. Additionally, the temperature at which the remelting process achieved optimal results was investigated. The AISI 4340 steel substrate samples were coated with a self-fluxing NiCrBSiCFe powder by APS. The post-coating remelting process was performed in a controlled atmosphere tube furnace at 900, 1000, and 1100 °C. Microstructural analysis was carried out by Scanning Electron Microscopy (SEM) before and after remelting. The estimated porosity of the as-sprayed sample was 3.28%, while the remelted coating sample at 1100 °C had only 0.22% porosity. Furthermore, a microhardness measurement was conducted, and the best condition yielded an average value of 750 HV0.5. Tribological tests were performed to evaluate the coefficient of friction and wear rates, revealing that at 1100 °C, the as-sprayed coating had a wear rate of 9.16 × 10−5 [mm3/(N*m] and the remelted coating had 4.106 × 10−5 [mm3/(N*m]. The wear-loss volume was determined to be 14.1 mm3 for the as-sprayed coating sample and 3.6 mm3 for the remelted coating at 1100 °C. [ABSTRACT FROM AUTHOR]

It is widely known that silicon carbide (SiC) is challenging to thermal spray.However, the nature of deposition and the underlying mechanisms are still not clearly understood. In the current work, the process of atmospheric plasma-sprayed SiC was investigated in detail. SiC exhibits sublimation severely under the plasma spraying (PS). More than 65 mol.% SiC particles lost by sublimation during PS estimated by calculation. Due to the nonuniformity of temperature in plasma flame, a small amount of SiC particles was retained. Moreover, a small amount of Si and SiO2 was experimentally observed after deposition process from the single-splat characterization. According to the first-principles calculations, the detachment energy of C atom from the lattice (0.591 eV) is lower than that of Si atom (1.257 eV). The adsorption energies of an O atom on the Si- and Cterminated surfaces are -9.549 and -7.631 eV, respectively. Therefore, C is more likely to form gaseous products after decomposition, and Si is more likely to be retained to form Si and SiO2. Mullite was found on the grain boundaries of molten Si, which was attributed to the rapid diffusion of the Al2O3 substrate along the grain boundaries of Si, promoting the spreading of molten splats. It is difficult to stack particles through self-diffusion among SiC particles to form coatings. The discovery on thermal depositionmechanism of SiC in PS is helpful to promote the practical application of SiC coatings on preparation optimization and interfacial bonding improvement. [ABSTRACT FROM AUTHOR]

In this research, a life cycle inventory (LCI) is developed for tungsten carbide–cobalt (WC-Co) coatings deposited via atmospheric plasma spray (APS), high-velocity oxy-fuel (HVOF), and cold gas spray (CGS) techniques. For the APS process, a mixture of Ar/H2 was used, while the HVOF process was fueled by H2. The carrier gas for CGS was N2. This study aims to determine and quantify the inputs (consumption of inputs and materials) and outputs (emissions to air, soil, water, and waste generation) that could be used in the life cycle analysis (LCA) of these processes. The dataset produced will allow users to estimate the environmental impacts of these processes using WC-Co feedstock powder. To obtain a complete and detailed LCI, measurements of electrical energy, gas, WC-CO powder, and alumina powder consumption were performed (the use of alumina was for sandblasting). Furthermore, emissions like carbon dioxide (CO2), carbon monoxide (CO), and noise were also measured. This practice allowed us to determine the input/output process quantities. For the first time, it was possible to obtain LCI data for the APS, HVOF, and CGS deposition processes using WC-12Co as a feedstock powder, allowing access to the LCI data to a broader audience. Comparisons were made between APS, HVOF, and CGS processes in terms of consumption and emissions. It was determined that the APS process consumes more electrical energy and that its deposition efficiency is higher than the other processes, while the HVOF process consumes a large amount of H2, which makes the process costlier. CGS has comparatively low electricity consumption, high N2 consumption, and low deposition efficiency. The APS, HVOF, and CGS processes analyzed in this study do not emit CO, and CO2 emissions are negligible. [ABSTRACT FROM AUTHOR]

Ultra-high temperature ceramic (UHTC) has been developed to protect C/C composites exposed to high-temperature oxidizing environment. In this study, the effect of additive for the ablation behavior of ZrB 2 -based coating was investigated. The SiC–La 2 O 3 bond coat was firstly prepared on the C/C composites by the method of pack cementation (PC). ZrB 2 –SiC–Si (ZSS) and ZrB 2 –SiC–Al 2 O 3 (ZSA) coatings with dense microstructure and excellent interfacial bonding then were prepared on the surface of C/C composites coated with SiC–La 2 O 3 layer by the method of atmospheric plasma spraying (APS). The ablation experiments of all coated samples were conducted under oxyacetylene torch with a heat flux of 4.18 MW/m2. The microstructure, phase compositions, interfacial bonding, ablation and oxidation behaviors of coating were investigated. After ablation test, the ZrO 2 sketon with prorous structure was formed in the central region of ZSS coating. However, denser structure still can be observed at ZSA coating due to the formation of liquid phase. The SiC–La 2 O 3 –C/C interface are still without cracks. Furthermore, the diffusion of La element into ZSS and ZSA coatings from the SiC–La 2 O 3 layer was beneficial for the improvement of ablation resistance. The result indicated that SiC–La 2 O 3 /ZSA could effectively provide protection for C/C composites. [ABSTRACT FROM AUTHOR]

The degradation of atmospheric plasma spraying (APS) thermal barrier coatings (TBCs) due to calcium-magnesium-alumina-silicate (CMAS) corrosion is considered as a critical issue. In present work, mitigation of CMAS infiltration of APS TBCs has been achieved by tailoring pore characteristics based on a novel APS structure regulation method, and its thermal conductivity, thermal shock lifetime and infiltration behavior were evaluated. The results revealed that the laminar pore distributed TBC formed by horizontally aligned porous embedded particle clusters (PEPC) showed longest thermal shock lifetime and lowest thermal conductivity. Characterization of CMAS corrosion suggested that whilst all the TBCs samples with different pore structures suffered corrosion by CMAS melt, the severity fluctuated greatly. Compared with randomly distributed PEPC areas, these horizontally aligned PEPC areas have a noticeable potential for restricting CMAS infiltration. This unique structure consumes a large amount of CMAS melt and creates anti-CMAS filling pores, thus improving the overall CMAS infiltration resistance of the coating. The alternating dense layers outside the porous layers also provide a layer-by-layer barrier to CMAS infiltration. This study emphasizes that the modulation of the pore structure of APS TBCs is a promising strategy to mitigate CMAS infiltration. [ABSTRACT FROM AUTHOR]

In this paper, the nanosilver particles were deposited onto the hydroxyapatite (HAP) microparticles and the obtained nanoAg-HAP particles were coated onto the Ti metal surface using the atmospheric plasma spray method. Then, the obtained nanoAg-HAP coating on Ti substrate was annealed at 700°C. The antibacterial activities of the nanoAg-HAP coatings on Ti were also tested against the microorganisms. The prepared nanoAg-HAP particles were examined using the optic microscopy, FE-SEM, HR-TEM, XRD and the UV-vis. absorption spectroscopy methods. The nanoAg particles exhibited crystalline spherical morphologies with the particle sizes below 30 nm. In the FE-SEM-EDS measurements, well distribution of nanoAg particles on the HAP microparticles were observed with Ag concentrations of 0.153% and 0.313%. The HR-TEM measurements showed that the nanoAg particles have hexagonal close packing (hcp) crystal structure with the d-spacing values of 0.23 nm (111), 0.21 nm (002) and 0.14 nm (022). After 700°C heat treatment, the prepared nanoAg-HAP coating on Ti metal showed 100% antibacterial activity against E. coli and S. epidermidis bacteria. As a result, the obtained nanoAg-HAP coated Ti metal can be utilized effectively as a self-disinfecting biomedical implant material in the orthopedic bone repairing of the body parts. [ABSTRACT FROM AUTHOR]

The objective of this study was to examine the characteristics of a nanostructured Yb2SiO5 coating and a conventional Yb2SiO5 coating, both prepared using atmospheric plasma spraying (APS). The investigation focused on the phase composition, microstructure, thermal properties, and fracture toughness of the two types of Yb2SiO5 coatings. The findings revealed that both nanostructured and conventional coatings consisted of Yb2SiO5, Yb2O3, and amorphous phases. The nanostructured Yb2SiO5 coating exhibited lower residual tensile stress compared to the conventional Yb2SiO5 coating, resulting in fewer crack defects in the former. The thermal conductivity of the nanostructured Yb2SiO5 coating ranged from 0.71 to 1.22 W/(m·K) between 200 and 1200 °C, while the conventional Yb2SiO5 coating exhibited a thermal conductivity range of 0.81–1.32 W/(m·K) within the same temperature range. Consequently, the thermal conductivity of the nanostructured Yb2SiO5 coating was lower than that of the conventional counterpart. Furthermore, the presence of nanograins significantly enhanced the fracture toughness of the nanostructured Yb2SiO5 coating, which was found to be 1.7 times greater than that of the conventional Yb2SiO5 coating.

The AlCoCrFeNi high entropy alloy bond coating was prepared by atmospheric plasma spray. The growth process and failure behavior of the thermally grown oxide (TGO) layer during the oxidation of the AlCoCrFeNi bond coating at 900–1000 °C were investigated. Results show that the AlCoCrFeNi bond coating generates a protective TGO layer composed of Al2O3 at 900–1000 °C, which effectively reduces the oxidation rate of the coating. The oxidation kinetic curves of the AlCoCrFeNi coating at 900–1000 °C exhibited a parabolic pattern. Until 50h oxidation, the TGO layer at 900 °C remained complete. In contrast, the TGO layer exfoliated at 1000 °C, associated with the thermal mismatch stress between the TGO layer and the AlCoCrFeNi coating. The growth of the TGO layer is primarily controlled by the outward diffusion of Al ions, which causes the generation of Al ion vacancies within the coating, consequently developing into visible pores. The presence of pores exacerbates the possibility of TGO layer exfoliation. The control of the outward diffusion process of Al ions, which can reduce the growth rate of the TGO layer and the amount of pores in the coating, is an important idea to improve the oxidation resistance of AlCoCrFeNi coating.

Hot corrosion and thermally grown oxide (TGO) formation are destructive factors in thermal barrier coatings (TBCs) that lead to coating failure under operational conditions. In the present study, the hot corrosion behavior and TGO evolution for TBCs whose Bond coat by deposited by atmospheric plasma spraying (APS) and high velocity oxygen fuel (HVOF) thermal spray methods were evaluated. Both types of coatings were subjected to cyclic hot corrosion testing at a temperature of 1100°C in the presence of molten salts of Na2SO4 and V2O5 under identical conditions. Subsequently, their microstructures were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD) images. Additionally, changes in TGO thickness were measured across different cycles using Image J software and SEM images. The results indicate that TBCs deposited using the HVOF method for the bond coat exhibit better performance compared to those deposited using the APS method. The results show that a phase change from tetragonal to monoclinic has occurred for zirconia with the penetration of corrosive salt melt and its reaction with the YSZ layer, and also with the depletion of yttria from the coating structure, YVO4 reaction products have been formed for TBCs. The endurance of hot corrosion cycle of TBCs and the growth behavior of TGO show that the coatings whose interface layer is applied by the HVOF method show better performance than the APS method. [ABSTRACT FROM AUTHOR]

Thermal Barrier Coatings (TBCs) have been the topic of scientific research and development in surface engineering. TBCs provide effective surface protection onto the hot components of gas turbines and aero engines, enabling them to operate at high inlet gas temperatures. This paper aims to present state-of-the-art research contributions to strengthen the understanding of growth and development in the ever-increasing field of TBCs. The paper emphasises and consolidates major research progress and contributions carried out in the literature and briefly surveyed in the two most promising research categories, viz. growth and development in deposition techniques for TBC and exploration of TBC materials. A review will help the research community to understand the existing deposition processes and their contribution to future needs. [ABSTRACT FROM AUTHOR]

Environmental barrier coatings for SiC/SiC composites are limited by the melting temperature of the Si bond coating near 1414 °C. Systems without a bond coating may be required for future turbine applications where material temperatures go beyond 1350 °C. Enhanced roughness SiC substrates were developed to assess coating adhesion without the bond coating. Two EBCs with different YbMS/YbDS ratios were produced via modified plasma spraying parameters. Coating microstructure, thermal expansion, and modulus were measured for comparison of coating properties. Cyclic steam exposures at 1350 °C were performed to assess oxidation resistance. The EBC with increased concentration of Yb 2 SiO 5 secondary phase displayed a higher CTE, which is typically expected to decrease adhesion lifetimes due to an increase in stress upon thermal cycling. Yet, the EBC chemistry with increased Yb 2 SiO 5 concentration was able to experience longer cycling times prior to coating delamination, likely due to interface interactions with the substrate and the thermally grown oxide. [ABSTRACT FROM AUTHOR]

Dy doped ceramic material of Ba4Fe2.6Dy1.4Nb8O30 with the tetragonal black bronze structure was synthesized by solid‐state reaction at 1300°C. The composite powders of Ba4Fe2.6Dy1.4Nb8O30/FeSiAl with good flowing were prepared by spray drying using the powders slurry. The obtained composite powders were then plasma sprayed to fabricate coating. The microstructure and absorption characteristics of electromagnetic wave (EMW) of the coating materials are investigated. Results show that the composite powders significantly remain the phase stability during atmospheric plasma spraying and adsorbing heredity of EMW for the coating. The coating powders have excellent EMW absorption with the minimum reflection loss of −48.20 dB at the thickness of 3.5 mm. Also, the coating powders display the maximum effective absorption bandwidth of 6.24 GHz at the thickness of 1.5 mm, which covers the X‐band. Moreover, the coating was found to have a certain EMW absorption performance at high temperature of 700°C. The Ba4Fe2.6Dy1.4Nb8O30 ceramic material with low thermal conductivity ensured the electromagnetic absorption capacity of the coating at high temperature. The Ba4Fe2.6Dy1.4Nb8O30/FeSiAl ceramic composite materials could have the potential applications as the high temperature EMW absorber. [ABSTRACT FROM AUTHOR]

SiC/SiC ceramic matrix composites (SiCf/SiC CMCs) are regarded as the new materials for the hot-section components of aircraft gas turbine engines, since they have one-third of the density of metallic superalloys, a higher temperature capability, good mechanical strength, and excellent thermal shock resistance. However, high-temperature water-vapor-rich combustion gases can induce severe surface recession phenomena in SiC/SiC leading to component failure. For this reason, it is necessary to design protective coatings, i.e., environmental barrier coatings (EBCs), able to protect the SiC/SiC surface in combustion environments. In the present work, ytterbium monosilicate (Yb2SiO5), stable when exposed to water vapor at high temperatures, and ytterbium disilicate (Yb2Si2O7), characterized by a thermal expansion coefficient closer to that of the substrate, were selected for a multilayer EBC system. EBCs were processed using the atmospheric plasma spray (APS) technique. A set of deposition parameters were tested, varying the power of the torch, and the composition and microstructure of the deposited coatings were studied in terms of porosity, crack density, and post-deposition phase retention by performing SEM, EDS, and XRD analysis. The results allow for the definition of the influence of deposition parameters on the final properties of multilayer EBC coatings. [ABSTRACT FROM AUTHOR]

The microstructural evolution of partially amorphous, atmospheric plasma-sprayed Yb-silicate coatings was investigated after heat treatment (HT, 1300 °C). Open porosity as well as crack area and widths in the coatings were characterized. A correlation was found between the increasing amorphous content of the as-sprayed coatings and the reduction in crack area due to crack healing after HT. Characterization results also suggested larger crack widths in the coatings after HT. The first crack-healing mechanism proposed was the capillarity-driven viscous flow of the amorphous phase in the coatings. It was experimentally shown that viscous flow-driven crack spheroidization (crack width enlargement), and crack healing started in the coatings at 1050 °C. Secondly, metastable to stable phase transformation (> 1100 °C) induced expansion in the constrained coatings was discussed as a crack healing mechanism. Finally, a two-step heat treatment was designed to prevent crack width enlargement during HT resulting in reduced porosity. [ABSTRACT FROM AUTHOR]

This study investigates the effect of annealing on the microstructural evolution, phase formation and tribological properties of CoCrFeNiW0.3 + 5 at.% C alloy prepared using atmospheric plasma spray. The annealing has a significant effect on microstructure evolution and tribological properties. The microstructure of the CoCrFeNiW0.3 + 5 at.% C alloy exhibits the lamellar microstructure. When the annealing temperature reaches 900 °C, the carbon dissolves in the chromium and forms Cr-rich carbides phase. The coarsening of grey phases is observed with the evolution of W-rich, and Cr-rich carbides as the temperature attain 1200 °C. Phase analysis results revealed that CoCrFeNiW0.3 + 5 at.% C alloy coating comprising of FCC solid solution phase, with Cr- and W-rich phase. As the annealing temperature increases from 900 to 1200 °C, more Cr- and W-rich phase evolved. The surface morphology results indicate the increase in the surface roughness value post-heat-treatment. The dilution level investigation reveals the strong metallurgical bonding between the coating and the substrate. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy reveal the formation of the oxidation state in detail. The average microhardness of the CoCrFeNiW0.3 + 5 at.% C alloy coating was found to be marginally decreased by increasing the annealing temperature, and the deposited coating microhardness was found to be 388.54 ± 14 HV0.2. The wear analysis test revealed a considerable decrease in wear resistance after heat treatment at 1200 °C. The wear volume rate of the as-deposited coating was found to be 7.88 × 10−5 mm3 N−1 m−1, and the coating annealed at 700, 900, and 1200 °C was 7.92 × 10−5, 8.02 × 10−5, 13.26 × 10−5 mm3 N−1 m−1, respectively. [ABSTRACT FROM AUTHOR]

The tribological behaviors of TiO 2 –ZnO and TiO x coatings deposited by atmospheric plasma spraying were studied to further explore the immanent tribological performance of the oxide system at high temperatures. The results show that both the plasma spraying fabrication process and the high temperature sliding process will lead to the phase transformation of the ceramic coatings. The tribological properties of TiO 2 –ZnO and TiO x ceramic coatings are temperature-dependent and can be improved with the increase in temperature except that of the TiO 2 –ZnO coating at 400 °C. The lower friction coefficients and wear rates of TiO 2 –ZnO coatings and TiO x coating at 800 °C are mainly related to the smooth film formation on both the worn surface of coatings and counterpart balls, consisting of high temperature lubricating oxides (A-TiO 2 , R–TiO 2 , Zn 2 TiO 4 , and Ti 8 O 15). [ABSTRACT FROM AUTHOR]

In this research, a life cycle inventory (LCI) is developed for tungsten carbide–cobalt (WC-Co) coatings deposited via atmospheric plasma spray (APS), high-velocity oxy-fuel (HVOF), and cold gas spray (CGS) techniques. For the APS process, a mixture of Ar/H2 was used, while the HVOF process was fueled by H2. The carrier gas for CGS was N2. This study aims to determine and quantify the inputs (consumption of inputs and materials) and outputs (emissions to air, soil, water, and waste generation) that could be used in the life cycle analysis (LCA) of these processes. The dataset produced will allow users to estimate the environmental impacts of these processes using WC-Co feedstock powder. To obtain a complete and detailed LCI, measurements of electrical energy, gas, WC-CO powder, and alumina powder consumption were performed (the use of alumina was for sandblasting). Furthermore, emissions like carbon dioxide (CO2), carbon monoxide (CO), and noise were also measured. This practice allowed us to determine the input/output process quantities. For the first time, it was possible to obtain LCI data for the APS, HVOF, and CGS deposition processes using WC-12Co as a feedstock powder, allowing access to the LCI data to a broader audience. Comparisons were made between APS, HVOF, and CGS processes in terms of consumption and emissions. It was determined that the APS process consumes more electrical energy and that its deposition efficiency is higher than the other processes, while the HVOF process consumes a large amount of H2, which makes the process costlier. CGS has comparatively low electricity consumption, high N2 consumption, and low deposition efficiency. The APS, HVOF, and CGS processes analyzed in this study do not emit CO, and CO2 emissions are negligible.

Materials with enhanced wear resistance are constantly in high demand. Nickel-based self-fluxing materials deposited by atmospheric plasma spraying (APS) have feasible wear resistance performance. This study aimed to evaluate the results of a nickel-based self-fluxing alloy coating deposited on AISI 4340 steel substrate using APS. Additionally, the temperature at which the remelting process achieved optimal results was investigated. The AISI 4340 steel substrate samples were coated with a self-fluxing NiCrBSiCFe powder by APS. The post-coating remelting process was performed in a controlled atmosphere tube furnace at 900, 1000, and 1100 °C. Microstructural analysis was carried out by Scanning Electron Microscopy (SEM) before and after remelting. The estimated porosity of the as-sprayed sample was 3.28%, while the remelted coating sample at 1100 °C had only 0.22% porosity. Furthermore, a microhardness measurement was conducted, and the best condition yielded an average value of 750 HV0.5. Tribological tests were performed to evaluate the coefficient of friction and wear rates, revealing that at 1100 °C, the as-sprayed coating had a wear rate of 9.16 × 10−5 [mm3/(N*m] and the remelted coating had 4.106 × 10−5 [mm3/(N*m]. The wear-loss volume was determined to be 14.1 mm3 for the as-sprayed coating sample and 3.6 mm3 for the remelted coating at 1100 °C.

MoO3 thick film was manufactured by using a thermal spray process (Atmospheric Plasma Spray, or APS) and its microstructure, phase composition and properties of the coating layer were investigated. Initial powder feedstock was composed of an orthorhombic α-MoO3 phase, and the average powder particle size was 6.7 μm. As a result of the APS coating process, a MoO3 coating layer with a thickness of about 90 μm was obtained. Phase transformation occurred during the process, and the coating layer consisted of not only α-MoO3 but also β-MoO3, MoO2. Phase transformation could be due to the rapid cooling that occurred during the process. The properties of the coating layer were evaluated using a nano indentation test. Hardness and reduced modulus were obtained as 0.47 GPa and 1.4 GPa, respectively. Based on the above results, the possibility of manufacturing a MoO3 thick coating layer using thermal spray is presented.

The aim of this paper is to define and set up an experimental procedure, based on active thermography, for the characterization of coatings for industrial applications. This procedure is intended to be a fast and reliable method, alternative to the consolidated one described in International Standards. In more detail, a classical active thermographic set up, and not a dedicated apparatus, was used for that aim, and data processing techniques referred to the analytical approach described in Standards. The active thermography procedure provided the measurement of the surface temperature of specimens undergoing a thermal excitation, applied by means of a laser pulse (Pulsed Technique). Temperature data processing, according to and adapting the Standard procedures, allowed to obtain thermal conductivity and diffusivity information. In particular, two coating processes (Atmospheric and Suspension Plasma Spray) applied to the same base material, Inconel 601, and the same coating material were investigated. These results were compared in terms of thermal properties variation with respect to base and coated materials, and in terms of different coating processes (APS and SPS). Obtained results were also compared to those available in literature.

This work aims to investigate microstructure and wear resistance of FeCoCrNi high-entropy alloy (HEA) coatings prepared by atmospheric plasma spraying (APS) at different spray powers. The density of the coatings is proportional to the spray power in the range of 15-25 kW. The room-temperature wear resistance of FeCoCrNi HEA coating sprayed under 25 kW power was the best with friction coefficient, wear rate and wear track depth to be (0.61 ± 0.02), (5.32 ± 0.02) × 10−5 mm3/(N·m) and (88.1 ± 10) μm, respectively. Abrasive wear, adhesive wear and plastic deformation were identified as the main wear mechanisms. Nano-mechanical properties of in situ formed oxides were much higher than those of metallic phases of HEA coating and feedstock. The friction coefficient, wear track depth and width, wear rate and wear mass loss of coated samples at 25 kW were first increased with temperature and then falling down at higher temperature. Main oxidation wear, supplemented with abrasive wear, adhesive wear and fatigue wear, was occurred during high temperature (≥ 400 °C) wear test. The wear resistance of HEA coatings was improved at high temperature attributed to solid lubrication from continuous oxide films formed on the worn surfaces of HEA coatings and Si3N4 balls. [ABSTRACT FROM AUTHOR]

Two types of high-entropy alloys (HEAs) AlCrCoFeNiTi and FeCrCoNiW0.3 + 5 at.% C are fabricated using atmospheric plasma spray (APS) technique. Laser surface processing (LSP) is performed on the developed alloys using Nd:YAG pulsed laser. Post processing the surface roughness of the alloys are reduced by ~ 29%. The impact of laser surface processing reveals the presence of a single BCC phase and FCC phase with the evolution of more W-rich and Cr-rich carbides in AlCrCoFeNiTi and FeCoCrNiW0.3 + 5 at.% C coatings, respectively. The microstructural study exhibits the formation of lamellar microstructure with minimum pores and interlaminar cracks. Post laser processing the microhardness of both the APS coated alloys are increased by 5%, nanoindentation results reveal an increase in the average elastic modulus (Er) by 12%, and average nanohardness by 18%. The FeCoCrNiW0.3 + 5 at.% C coatings achieved maximum wear resistance of 39.71% among the two alloys, indicating the improvement achieved through laser processing. Also the observed improvements in surface morphology of both the alloys are reported. [ABSTRACT FROM AUTHOR]

Atmospheric plasma spray (APS) remains the only certified industrial process to produce hydroxyapatite (Hap) coatings on orthopaedic and dental implants intended for commercialization. Despite the established clinical success of Hap-coated implants, such as hip and knee arthroplasties, a concern is being raised regarding the failure and revision rates in younger patients, which are increasing rapidly worldwide. The lifetime risk of replacement for patients in the 50–60 age interval is about 35%, which is significantly higher than 5% for patients aged 70 or older. Improved implants targeted at younger patients are a necessity that experts have been alerted to. One approach is to enhance their bioactivity. For this purpose, the method with the most outstanding biological results is the electrical polarization of Hap, which remarkably accelerates implant osteointegration. There is, however, the technical challenge of charging the coatings. Although this is straightforward on bulk samples with planar faces, it is not easy on coatings, and there are several problems regarding the application of electrodes. To the best of our knowledge, this study demonstrates, for the first time, the electrical charging of APS Hap coatings using a non-contact, electrode-free method: corona charging. Bioactivity enhancement is observed, establishing the promising potential of corona charging in orthopedics and dental implantology. It is found that the coatings can store charge at the surface and bulk levels up to high surface potentials (>1000 V). The biological in vitro results show higher Ca2+ and P5+ intakes in charged coatings compared to non-charged coatings. Moreover, a higher osteoblastic cellular proliferation is promoted in the charged coatings, indicating the promising potential of corona-charged coatings when applied in orthopedics and dental implantology. [ABSTRACT FROM AUTHOR]

The primary focus of the study is to explore the influence of annealing on the various properties like phase formation, microstructure evolution and wear analysis of equiatomic AlCoCrFeNiTi high entropy alloy (HEA) coatings developed by atmospheric plasma spray technique. Post deposition, annealing was performed at three different temperatures of 700 °C, 900 °C and 1200 °C, respectively, for a time period of 180 min. X-ray diffraction (XRD) studies revealed that AlCoCrFeNiTi HEA coating comprises two BCC solid solution phases. The deposited samples were characterized using scanning electron microscopy (FESEM), surface profilometer, chemical analysis using x-ray photoelectron spectroscopy (XPS) and Fourier transform infra-red spectroscopy (FTIR). The dilution level study revealed the strong metallurgical bonding between coating and substrate. Microhardness of the AlCrCoFeNiTi was found to be marginally decreased by increasing the annealing temperature due to coarsening of grains and the deposited coating microhardness was found to be 768.48 ± 16 HV0.2. Wear test analysis performed using the ball-on disc test revealed that, there is a significant decrease in wear resistance after heat treatment at 1200 °C. Beyond 900 °C, annealing decreased the microhardness and wear resistance due to coarsening of grains. The wear volume rate of the unannealed as-deposited coating was found to be 2.8 × 10–7 mm3 N−1 m−1 and the coating annealed at 700 °C, 900 °C, and 1200 °C had a wear volume rate of about 2.89 × 10–7 mm3 N−1 m−1, 2.87 × 10–7 mm3 N−1 m−1, 7.29 × 10–7 mm3 N−1 m−1, respectively. [ABSTRACT FROM AUTHOR]

In this study we analyzed the rolling contact fatigue behavior of two types of coatings made by thermal coating, by the method of atmospheric plasma spraying (APS) from two commercially available powders: Ni5Al5Mo and Al2O3 – 13 TiO2. The contact fatigue behavior was studied on an installation specially designed. The specimens were tested for 54 hours (at 1380 rpm), at a load of 944 N. For both types of coatings, the appearance of a wear path was observed, much more obvious in the case of the Ni matrix layer, also confirmed by profilometry. The mechanism of the wear phenomenon was predominantly of plastic deformation type (the material was pushed towards the edges of the wear path) in the case of NiAlMo coating. In the case of ceramic coating, the wear path width was very small (300-450 μm), with very few changes at the surface level of the coating, which recommends this type of material for applications that require wear resistance to rolling.

The plasma sprayed 8YSZ TBC is applied on a Ti-6Al-4V substrate with a NiCrAlY bond coat. The effect of spray angle on the coating microstructural, residual stresses, and mechanical properties is studied in the paper. The surface and cross-sectional coating structure were analyzed by scanning electron microscopy and elemental composition with energy-dispersive x-ray spectroscopy. The SEM image greyscale threshold determined the porosity level in the structure. The residual stresses and thermal conductivity were measured by Raman spectroscopy and laser flash technique. The mechanical property, such as hardness and surface roughness was determined using the indentation and surf test profilometer. The result showed that the spray angle affects the coating structure - grain size, shape and distribution, and mechanical properties. The P90 TBC showed a uniform and dense structure with avg. grain size of ~ 850nm, whereas P60 showed a non-uniform structure with avg. grain size of ~ 300nm. The 60° inclined spray angle leads to more defects such as cracks and pores than the 90° normal spray angle. In both surface and cross-sectional structures, the porosity level increases with a decrease in the spray angle conditions. The P90 TBC results in high compressive residual stresses than the P60 structured TBC. The avg. Raman shifts for P90 and P60 TBCs are 1.5667±1.022cm-1 and 1.3±0.973cm-1, respectively. The thermal conductivity decreases with increased porosity and low spray angle. The P90 showed better hardness and uniform surface than P60 TBC.

Passive thermal probes were applied on two different plasma spraying devices to gain a detailed understanding of the energy flux towards the substrate under atmospheric pressure. The challenge of very high thermal load was solved by using an advanced time-resolved measuring and evaluation technique. The combination with a controlled movement of the jets allowed to obtain insightful radial profiles. The energy flux to the substrate changes linearly to the electrical input power. When adding diatomic gases (H2/N2) to the gas mixture the energy flux increases significantly, suggesting a more efficient energy transport. For increasing the axial distance, the energy flux shows a quadratic reduction. The obtained radial profiles are exemplarily utilized to show the inhomogeneous effect of powder injection on the energy flux distribution. [ABSTRACT FROM AUTHOR]