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Zircon (ZrSiO 4) is an inexpensive and widely available material with excellent thermal properties that makes it an ideal candidate for thermal barrier coatings. Previous works have demonstrated the feasibility of obtaining coatings with a high retention of zircon by plasma spraying of ZrSiO 4 and ZrSiO 4 /ZrO 2 suspensions. Suspensions of ZrSiO 4 /Al 2 O 3 and ZrSiO 4 /TiO 2 were produced by dispersing a micrometric zircon powder into alumina and titania colloidal sols, optimising their colloidal stability and rheological behaviour. Optimised slurries were plasma sprayed onto metallic substrates, obtaining coatings with the typical morphologies obtained by suspension plasma spraying (SPS). Nanostructured coatings with nanoparticles embedded in the molten matrix were obtained at higher proportions of sprayed colloidal sol. The high retention of ZrSiO 4 in the final coatings and the formation of new crystallographic phases of mullite and zirconium titanate by reaction of the by-products of zircon decomposition (SiO 2 and ZrO 2) and the Al 2 O 3 and TiO 2 colloids was demonstrated. [ABSTRACT FROM AUTHOR]

Understanding the damage evolution of thermal barrier coatings (TBCs) is crucial for optimizing TBCs systems and predicting service lifetime. This study investigates the correlation between mechanical properties and the thermal cycle lifetime of TBCs with conventional air plasma sprayed (APS) and micro-agglomerated particles embedded (EMAP) plasma sprayed structures, utilizing the Gd 2 Zr 2 O 7 (GZO) and GSc 0.075 Ce 0.3 Z (GSCZ) material systems. The damage evolution and cracking behavior of TBCs with varying material compositions and coating structures are evaluated using a combination of three-point bending tests and digital image correlation (DIC) techniques. Experimental results demonstrate that the thermal cycling lifetime of conventional APS TBCs correlates positively with the fracture toughness of the ceramic layer. Specifically, the conventional APS GSCZ coating with a fracture toughness of 1.12 MPa/m1/2 and the APS GZO coating with a fracture toughness of 0.97 MPa/m1/2 exhibit lifetimes of 34 cycles and 31 cycles, respectively. Moreover, the EMAP structural design exhibits notable advantages in enhancing the thermal cycle lifetime of TBCs across all material systems. DIC results confirm that strain accumulation during interface cracking of EMAP TBCs is effectively mitigated compared to conventional APS TBCs. The loose and porous characteristics of this structure significantly improve the compliance and interface fracture toughness of the TBC system, thereby alleviating TBC failure dominated by interface cracking. [ABSTRACT FROM AUTHOR]

The performance of plasma sprayed thermal barrier coatings (TBCs) is strongly dependent on the quality of the feedstock powders, which usually are fabricated by conventional spray drying and multi-step sintering methods. In this work, a novel supersonic plasma spheroidization technology was employed to fabricate the spherical nanocrystalline Sc 2 O 3 -Y 2 O 3 co-stabilized ZrO 2 (ScYSZ) powder. The deformation process from the irregular powder to the spherical one was stimulated by the COMSOL phase field simulation. The results suggested that the original irregular pyrolysis products of ScYSZ precursors were aggregated into spherical powders by plasma spheroidization technology. The COMSOL simulations verified that the powder changed from irregular particles to spherical ones. The spheroidized ScYSZ particles exclusively consisted of non-transformed t' -ZrO 2 phase and showed good fluidity, smooth surface and high apparent density, which were expected to have a broader application prospect in the field of TBCs and other ceramic coatings. [ABSTRACT FROM AUTHOR]

Superalloys go through cyclic oxidation which refers to the progression of reputed exposure of materials to alternating oxidizing and non-oxidizing environments at high temperatures. The oxidation behavior of cobalt-based superalloy coatings depends on several variables, including the environment, surface roughness, manufacturing conditions, & coating composition. Because of their higher temperatures and protective oxide layer, coatings with a greater cobalt concentration are more oxidation-resistant. The behavior of oxidation is influenced by surface roughness, where rough surfaces offer greater surface area to oxidation while smooth surfaces decrease interaction with the environment. The microstructure and porosity of the coating are further impacted by processing variables used in thermal spraying, including temperature, particles velocity, and spray distance. Adding reactive components to the coating composition, such as silicon and aluminum, and applying post-treatments like nitriding or sealing are two ways to increase oxidation resistance. A greater temperature and particle speed can lead to a denser with less porous covering, improving the oxidation process resistance. The two typically used heat spraying techniques are high-velocity oxy-fuel (HVOF) and plasma spraying. To increase the resistance to oxidation of thermal spray cobalt-based superalloy coating, some strategies have been devised, such as inclusion of reactive materials, such as aluminum and silicon, which is the coating composition. These elements may establish an oxide layer protecting the coating's appearance, preventing further oxidation. [ABSTRACT FROM AUTHOR]

Achieving high crystallinity levels, dense, crack-free microstructures with near-stoichiometric phase composition and controlled secondary phase formation are crucial for enhancing the performance of environmental barrier coatings (EBCs). To investigate the impact of APS process parameters on the as-sprayed crystallinity, microstructure, and phase composition of Yb 2 Si 2 O 7 EBCs, various spraying conditions were explored by adjusting torch power, nozzle size, powder feedrate, stand-off distance, and adding a shroud attachment to the torch. The velocity of particles controlled the density of the EBCs by an interplay between deposition efficiency and splat flattening ratios. Increasing nozzle size from 5/16″ to 1/2″ reduced particle velocity by up to 40 %, resulting in improved deposition efficiencies, porosity levels and coating thickness. However, larger nozzles led to higher silicon evaporation and up to 8 wt% more stable Yb 2 SiO 5 (I2/a) secondary phase was formed. Increasing the stand-off distance from 50 mm had minimal effect on microstructure, but metastable Yb 2 SiO 5 (P 21/c) was detected (up to 9 wt%) at longer stand-off distances of 100 and 150 mm. Raising the powder feedrate from 15 gr/min to 60 gr/min improved deposition efficiency (up to 9 %) and density (up to 15 %) of EBCs, yet resulted in higher silicon-depleted phase formation (up to 12 wt%). Adding a shroud to the torch nozzle exit led to severe silicon evaporation and formation of up to 42 wt% and 6 wt% of Yb 2 SiO 5 (I2/a) and Yb 2 O 3 , respectively. Moreover, due to the shroud's funnelling effect on smaller particles as well as particle overheating, porous microstructures with up to 28 % porosity levels were formed. High levels of crystallinity (∼75–91 %) were achieved in the as-sprayed condition for all the coatings, indicating real-time crystallization during spraying in all the spraying conditions. [ABSTRACT FROM AUTHOR]

This paper presents and demonstrates the development of a new lightweight coating for aluminum alloy from a novel multicomponent alloy based on the AlSiMgCu system. The coating was applied using a newly designed approach that combined high velocity oxy-fuel (HVOF) and plasma spraying processes. This hybrid technique enables the deposition of coatings with enhanced performance characteristics. The optical microscopy (OM) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM + EDS) revealed a strong adhesion and compaction between the multicomponent coating and the A6061 substrate. The new coating improved hardness by 50% and increased electrical conductivity by approximately 3.3 times compared to the as-cast alloy. Corrosion tests showed a lower corrosion rate, comparable to thermally treated A6061 alloy. Tribological tests indicated over 20% reduction in friction and over 50% reduction in wear rate. This suggests that multicomponent aluminum coatings could improve automotive and parts in contact with hydrogen by enhancing hydrogen fragilization resistance, corrosion resistance, electrical conductivity, and wear properties, with further optimization of thermal spraying potentially boosting performance even further. [ABSTRACT FROM AUTHOR]

Yb-doped Y2O3 stabilized ZrO2 (YbYSZ) coatings, developed through solution precursor plasma spraying (SPPS), are engineered to resist calcium–magnesium–alumino–silicate (CMAS) infiltration by leveraging their unique micro-nano structures. This provides superior anti-wetting properties, crucial for preventing CMAS penetration at high temperatures. The investigation focused on the structural and compositional changes in YbYSZ-SPPS coatings subjected to prolonged thermal exposure at 1300 °C. Results indicate that while the coatings undergo significant sintering, leading to densification and microstructural evolution, the elemental composition and phase stability remain largely intact after up to 8 h of heat treatment. Despite some reduction in CMAS resistance, the coatings maintained their overall protective performance, demonstrating the potential of SPPS coatings for long-term use in high-temperature environments where CMAS infiltration is a concern. These findings contribute to the development of more durable TBCs for advanced thermal protection applications. [ABSTRACT FROM AUTHOR]

This paper presents a study on thermally sprayed coatings. Coatings produced by high-velocity oxygen–fuel spraying HVOF and plasma spraying deposited on the A03590 aluminum casting alloy are tested. The subject of this research concerns coatings based on tungsten carbide WC, chromium carbide Cr3C2, composite coatings NiCrSiB + 2.5%Fe + 2.5%Cr, mixtures of tungsten and chromium powders WC-CrC-Ni, mixtures of carbide powders with the Cr3C2-NiCr + the composite 5% NiCrBSi and WC-Co + 5% NiCrBSi. The aim of this research is to find a coating most resistant to the erosive impact of particles contained in the medium centrifuged by industrial rotors. The suitability of the coating is determined by its high level of microhardness. The hardest coatings are selected from the coatings tested and subjected to abrasion tests against a sand particle impact jet and the centrifugation of a medium with corundum particles. It is found that the most favorable anti-erosion properties are demonstrated by a coating composed of a mixture of tungsten carbide and chromium carbide WC-CrC-Ni powders. It is concluded that the greatest resistance of this coating to the erosive impact of the particle jet results from the synergistic enhancement of the most favorable features of both cermets. [ABSTRACT FROM AUTHOR]

This document is a list of articles published in the journal "Thermal Spray Technology" between 1992 and 2010. The articles cover a range of topics related to thermal spraying, including the formation of coatings, particle behavior during spraying, and the properties of different types of coatings. Professor Pierre Léon Fauchais, a highly respected figure in the field, passed away in 2024 at the age of 86. He made significant contributions to the scientific community over six decades, serving as a mentor and guide to many scientists and engineers. His legacy in the field of thermal spraying is widely recognized and respected. [Extracted from the article]

Wire thermal spraying, one of the significant coating preparation technologies in the field of thermal spraying, has the advantages of low cost, high material utilization rate and fast coating deposition. Powder-cored wires, with easily controllable compositions, are used as spraying materials to prepare functional coatings with special properties. Coatings prepared by traditional wire thermal spraying technologies, mainly including wire flame spraying (WFS), wire arc spraying (WAS) and plasma wire spraying, have some defects, such as weak bonding strength and high porosity. In this paper, the plasma transferred wire arc spraying (PTWAS) technology was innovatively proposed, by which Al/SiC powder-cored wires were successfully sprayed to deposit the aluminum (Al)/Nicalon (SiC) composite coating. Furthermore, the influences of spraying current (I), argon (Ar) flow rate (LAr), hydrogen (H2) flow rate (LH2) and other factors on Al/Sic powder-cored wires prepared by PTWAS and the optimization of the coating preparation process were mainly studied via the single factor method and the response surface methodology. After experimental exploration and analysis, the optimized process parameters were finally determined as follows: LAr was 120 L min−1, I was 160 A, LH2 was 5 L min−1, the spraying distance was 100 mm, the wire feeding speed (V) was 0.18 m s−1, and the distance between the wire and nozzle (d) was 10 mm. It was found in the test that the porosity of the optimized Al/SiC composite coating was only 1.6%, the average microhardness was 102 HV0.1, and the average bonding strength was 36.5 MPa. The comprehensive properties of this coating were better than those of the Al/SiC composite coatings prepared by WFS and WAS. [ABSTRACT FROM AUTHOR]

The graphite/Al2O3 composite was prepared using plasma spray technology, the material design, experimental methods, and process flow are introduced. The microstructure, chemical composition, and complex permittivity of the composite are investigated, and its performance to absorb electromagnetic waves is studied. The mechanism of interaction between chemical composition, microstructure, complex permittivity, and absorption performance is analyzed. Furthermore, a microwave absorber composed of graphite/Al2O3 and sheet resistance, and performance is discussed. The reflectivity of the composite coating with different periods and sizes and resistances is analyzed. The impedance and reflectivity of the designed absorber that contains sheet resistance are discussed, and its absorption mechanism is explained in detail. The results demonstrate that the microwave absorption performance of graphite/Al2O3 coating is enhanced by electromagnetic resonance of the sheet resistance. The designed absorber exhibits good wave‐absorbing performance and stability at the frequency of the 8.2–18 GHz range. When the sample thickness is 2.3 mm, the absorber achieves a reflection loss (RL) value of −16.8 dB at 9.8 GHz and a wide effective absorption bandwidth (EAB) of 9.8 GHz. It means that the RL below −10 dB can be obtained in the whole X band and Ku bands. These results proved that the EAB can be tuned and enhanced by manipulating sheet resistance. [ABSTRACT FROM AUTHOR]

Temperature control of mould surfaces is of high relevance for part quality in moulding processes. Due to highly dynamic heating behaviour, heating elements applied by thermal spraying can be an alternative to existing tempering methods. To ensure the feasibility of these heating coatings on industry‐relevant moulds, the coating system needs to be applied onto more demanding non‐flat geometries. For this purpose, the spray angle of the plasma spraying process is varied during the application of the titanium oxide/chromium oxide heating coating and the insulating aluminium oxide coating. Subsequently, the results are related to application‐oriented cavity shapes. Spray angle deviations from the optimal perpendicular angle are leading to decreasing dielectric strength of the coating system and an increase of the electrical resistivity. Additionally, the application efficiency reduces with the spray angle variation. Knowledge of the spray angle's influence on coating properties can help to coat more demanding shapes, including free formed surfaces or corners. [ABSTRACT FROM AUTHOR]

The aim is to investigate the effect of critical plasma spraying parameter (CPSP) on the mechanical properties and thermal shock resistance of a novel (Y 0.2 Yb 0.2 Sc 0.2 Gd 0.2 Lu 0.2) 2 Si 2 O 7 high-entropy environmental barrier coating prepared by plasma spraying. Based on a modified Vickers indentation method, the residual stress and fracture toughness of coatings were evaluated, and then the relationship between the CPSP value and thermal shock lifetime of coatings was also established. As a result, the residual compressive stress of (Y 0.2 Yb 0.2 Sc 0.2 Gd 0.2 Lu 0.2) 2 Si 2 O 7 coating is reduced from -(53.24 ± 6.78) MPa to -(17.97 ± 3.04) MPa with the CPSP value decreases from 1.17kW/Lpm to 0.94kW/Lpm, while the corresponding fracture toughness exhibits an increasing tendency. The combination of higher fracture toughness and lower residual stress result in better thermal shock resistance for the coating, and the longest thermal shock lifetime of (136 ± 16) cycles for the coating deposited with a CPSP value of 0.94kW/Lpm is obtained during thermal shock test at 1350 °C. [ABSTRACT FROM AUTHOR]

Higher operating temperatures for gas turbine engines require highly durable thermal barrier coatings (TBCs) with improved insulation properties. A suspension plasma spray process (SPS) had been developed for the deposition of columnar-structured TBCs. SPS columnar TBCs are normally achieved at a short standoff distance (50.0 mm–75.0 mm), which is not practical when coating complex-shaped engine hardware since the plasma torch may collide with the components being sprayed. Therefore, it is critical to develop SPS columnar TBCs at longer standoff distances. In this work, a commercially available pressure-based suspension delivery system was used to deliver the suspension to the plasma jet, and a high-enthalpy TriplexPro-210 plasma torch was used for the SPS coating deposition. Suspension injection pressure was optimized to maximize the number of droplets injected into the hot plasma core and achieving the best particle-melting states and deposition efficiency. The highest deposition efficiency of 51% was achieved at 0.34 MPa injection pressure with a suspension flow rate of 31.0 g/min. With the optimized process parameters, 1000 μm thick columnar-structured SPS 8 wt% Y2O3-stabilized ZrO2 (8YSZ) TBCs were successfully developed at a standoff distance of 100.0 mm. The SPS TBCs have a columnar width between 100 μm and 300 μm with a porosity of ~22%. Furnace cycling tests at 1125 °C showed the SPS columnar TBCs had an average life of 1012 cycles, which is ~2.5 times that of reference air-plasma-sprayed dense vertically cracked TBCs with the same coating thickness. The superior durability of the SPS columnar TBCs can be attributed to the high-strain-tolerant microstructure. SEM cross-section characterization indicated the failure of the SPS TBCs occurred at the ceramic top coat and thermally grown oxide (TGO) interface. [ABSTRACT FROM AUTHOR]

Dual phase high entropy ceramics (DPHECs) exhibit excellent high temperature mechanical properties and oxidation resistance. Nevertheless, they cannot be applied in the structural components on large scale due to their intrinsic brittleness. Hence, DPHEC coating is a necessary development direction for industrial applications. In this study, we first fabricated micron-order DPHEC powder with high quality by precursor synthesis, spray drying (SD), and induction plasma spheroidization (IPS). The DPHEC coating was prepared by supersonic atmospheric plasma spraying (SAPS). The microstructure, phase compositions, and mechanical properties of the DPHEC powder and coating are investigated in detail. Results show that the SD&IPS powder and SAPS coating are all composed of HEB and HEC phases, showing slight composition segregation and typical global eutectic microstructure. The nanohardness and Young's modulus are 22.17 ± 2.76 GPa and 309.79 ± 35.71 GPa, respectively. The fracture toughness was calculated to be 2.23 ± 0.17 MPa m1/2 from the energy analysis method. The mechanical properties are enhanced by the solid solution and fine grain strengthening effects and are weakened by the intrinsic defects of plasma sprayed coating. This work provides a new method and a potential material for thermal spraying ultra-high temperature ceramic coatings. [Display omitted] [ABSTRACT FROM AUTHOR]

Graphene and nanodiamond are marvelous materials for wear-resisting coating, whose enhanced tribological properties are essential for its industrial development. Using a plasma spray process, we developed a method to fabricate graphene, nanodiamonds composite coating using the thermal spray coating technique. Nanodiamonds (0.1 wt.%) and Graphene nanoplatelets (GNP:1 wt.%) reinforced in Al2O3 hybrid carbon coating were deposited onto the (AISI 1020) steel substrate. Addition of 0.1 wt.% of ND and 0.1 wt.% of ND + 1 wt.% of GNP in alumina matrix has significantly enhanced relative density up to 97.25%, and improved wear resistance and wear rate at higher load are obtained. However, COF decreases with increasing loads. The maximum decrement in COF has been observed in 0.1 wt.% of ND + 1 wt.% of GNP in all the cases with decreasing drifts due to the self-lubricating properties of reinforced graphene nanoparticles and graphitization effect on the worn wear track during wear. [ABSTRACT FROM AUTHOR]

Ytterbium disilicate (Yb2Si2O7) is a potential environmental barrier coating (EBC) material. In this paper, the microstructure and phase composition of plasma‐sprayed Yb2Si2O7 coatings with different spraying process were systematically investigated to optimize the spraying power and spraying distance. Furthermore, in order to obtain Yb2Si2O7 coating with single phase, a certain proportion of SiO2 was added to the Yb2Si2O7 powder to compensate for the volatilization of SiO2 during plasma‐spraying process, and the influence of spraying powder composition on the microstructure and phase structure (composition and content) of Yb2Si2O7 coatings were also characterized in detail. The results showed that the Yb2Si2O7 coating was dense with fewer pores and cracks at the spraying power of 40 kW and the spraying distance of 100 mm. Yb2Si2O7 coating with the "sandwich" structure was composed of Yb2Si2O7, Yb2Si2O7 + Yb2SiO5, and Yb2SiO5 three microstructures, which was mainly caused by the volatilization of SiO2 in Yb2Si2O7 spraying powder. The Yb2Si2O7 coating contained 90.68 mol.% Yb2Si2O7 phase and 9.32 mol.% Yb2SiO5 phase after crystallization at 1300°C for 20 h. The coating was composed of Yb2Si2O7 phase and amorphous phase after SiO2 addition. Yb2SiO5 phase precipitated from the coating after heat treatment at 1300°C, and its content decreased with the increase of SiO2 content. The content of the Yb2Si2O7 phase was as high as 99.41 mol.% when SiO2 content was 10 mol.%, which would provide a scientific basis for further research on stoichiometric Yb2Si2O7 EBCs with excellent properties. [ABSTRACT FROM AUTHOR]

Nanostructured ceramic coatings are a promising research hotspot in the field of thermal protection coatings. Suspension plasma spraying is a practical thermal spaying technique to produce nanostructured thermal barrier coatings. In this paper, nanostructured 8YSZ (8 wt.% yttria-stabilized zirconia) thermal barrier coatings were fabricated using feedstocks of nano-8YSZ suspension by suspension plasma spraying, which was improved from air plasma spraying equipment attached to the atomizer feedstock device. Coatings microstructural analysis and testing were carried out by scanning electron microscope (SEM), and porosity was measured in cross-sectional SEM micrograph. The single scanning deposition status of 8YSZ coatings was investigated, analyzing SEM micrographs of single scanning coatings using different process parameters that included other solvents and additional locations in the plasma jet. The results show that deposition efficiency is higher using alcohol as a solvent, and a better melting state existed in the middle of the plasma jet. The cross-sectional microstructures in different thickness coatings were comparatively researched. More defects were observed in the microstructure of thicker coating, which can be produced by more residual thermal stress. This dramatically improves the thermal cycling performance of the coating. [ABSTRACT FROM AUTHOR]

Enhancing the durability and extending the service life of concrete are crucial for promoting its sustainable development. Applying surface coatings is the primary technical method used to improve concrete durability. In this study, based on the plasma thermal spraying technology, a thermal-sprayed, ceramic-based coating was prepared on a concrete surface and evaluated using the drawing method, X-ray diffraction scanning electron microscopy with energy dispersive spectroscopy, X-ray computed tomography (X-CT), and frictional wear. Subsequently, performance tests were conducted. The test results showed that mullite powder was a suitable ceramic-based coating material. The coating had a good interfacial bonding ability with the concrete surface; moreover, the bonding site exhibited a chimeric state with an adhesion strength of 3.82 MPa. The wear rate of the coating material (0.02‰) is lower than that of the concrete matrix (0.06‰), resulting in improved surface wear resistance. SEM analysis reveals that the coating contains a considerable amount of amorphous or microcrystalline phases. The internal structure of the coating exhibits porous characteristics, with a total porosity of 10.35% and pore diameters predominantly ranging from 4 μm to 16 μm. At a distance of 80 μm from the coating site, the elements Al, O, and Si significantly contribute to the mullite components. The porous structures within the coating products are further verified using X-CT. This study offers a new possibility for ceramic coatings on hydraulic concrete. [ABSTRACT FROM AUTHOR]

This study comparatively analyzed the wear characteristics and adhesion properties of 86WC–10Co–4Cr (WC) coatings deposited using the high velocity oxygen fuel process and 75Cr3C2–25NiCr (CrC) and Al2O3–3TiO2 (Al2O3) coatings deposited using the atmospheric plasma spray process on an A390 aluminum alloy substrate. The adhesion strength and wear test results demonstrated that the WC coating exhibited superior wear resistance. In contrast, the CrC and Al2O3 coatings showed lower adhesion properties and unstable frictional variations due to a higher number of defects compared to the WC coating. The WC coating layer, protected by WC particles, exhibited minimal damage and a low wear rate, followed by CrC and Al2O3. Ultimately, WC coating is highlighted as the optimal choice to enhance the wear resistance of A390 aluminum alloy. [ABSTRACT FROM AUTHOR]

Oxidation of the bond coat during turbine operation leads to additional stresses in the thermal barrier coating (TBC) system that promotes spalling of the thermal insulation. Therefore, the oxidation behavior of a TBC system plays an important role in the thermal cycling of a TBC system. To delay the loss of thermal insulation, research has typically focused for a long time on the composition and microstructure of the ceramic topcoats and metallic bond coats. More recently, heat treatment for the diffusion annealing of the bond coat has also become a focus of research. Several studies have shown that pre-oxidation of the bond coat prior to the application of the ceramic topcoat slows down the subsequent oxidation of the bond coat in service. The improved thermal cyclability has been demonstrated in studies for systems with atmospheric plasma-sprayed (APS), suspension plasma-sprayed (SPS) or electron beam physical vapor deposition (EB-PVD) top coatings. However, no study has directly compared the effects of pre-oxidation on different topcoats. Therefore, this study compared the effect of pre-oxidation on APS and SPS coatings with the same bond coat. For both topcoats, pre-oxidation slowed the subsequent TGO growth and thus increased the lifetime of the coatings. The improvement in lifetime was particularly pronounced for the systems with an SPS topcoat. Overall, the lifetime of the coatings with an APS topcoat was higher as the critical energy release rate within the coating was not exceeded in these coatings. [ABSTRACT FROM AUTHOR]

A series of self-lubricating multicomponent coatings (PS series) was developed in the early 1970s to provide low friction and low wear rates while keeping its chemical stability at elevated temperatures. Two compositions of such series, the PS304 (NiCr–Cr2O3–Ag–BaF2/CaF2) and PS400 (NiMoAl–Cr2O3–Ag–BaF2/CaF2), are well-established coatings which have shown promising tribological results when tested at a wide range of temperatures. These coatings are candidates to be used on engine parts that may be exposed to corrosive salts at elevated temperature (hot corrosion), but limited data in the open literature are available on the behavior of these coatings under such conditions. Thus, in this study, the hot corrosion and oxidation behavior of PS304 and PS400 coatings were assessed when exposed to a mixture of Na2SO4 and MgSO4 at temperatures ranging from 550 to 950 °C. The coatings were characterized by Raman, scanning electron microscopy, and X-ray diffraction to determine failure mechanisms and corrosion by-products. The PS304 coating has shown to be more prone to oxidation and hot corrosion attack, while PS400 has shown a more stable behavior, even at the highest testing temperature. Based on these results, different mechanisms of oxidation and hot corrosion are proposed for both coatings. [ABSTRACT FROM AUTHOR]

With the development of human-cyber-physical-production systems in intelligent manufacturing, cyber-supported production based on artificial intelligence is becoming an increasingly powerful means of controlling machines and collaborating with human users. Semi-autonomous systems with a medium degree of automation enable human-centered, flexible, and sustainable production, for instance, in hybrid decision-making. Especially in applications that do not meet the requirements for full automation and when humans are to be involved in their role as qualified decision-makers, teaming-capable systems are desirable and offer considerable advantages. This paper outlines the transdisciplinary concept of human–machine teaming and the role of human cognition in engineering tasks with multi-criteria decision-making. An illustrative real-life example from thermal spray technology is used to show how explainable artificial intelligence models offer targeted, hybrid cyber decision support. This new approach based on fuzzy pattern classifiers combines expert knowledge- and data-based modeling and enables a transparent interpretation of the results by the human user, as shown here using the example of test data from atmospheric plasma spraying. The method outlined can potentially be used to provide hybrid decision support for a variety of manufacturing processes and form the basis for advanced automation or teaming of humans and cyber-physical-production systems. [ABSTRACT FROM AUTHOR]

The Al2O3/ZrO2 coatings (AZ-Cs) with different ZrO2 contents were prepared via Al-Zr(NO3)4 combustion-assisted thermal spraying (CATS) method, and its microstructure evolution, mechanical properties were analyzed by experimental observation and finite element simulation. The results show that along the solidification direction, AZ-Cs contain four different microstructure regions of nano-crystalline, nano-eutectic, equiaxial eutectic and submicron eutectic. The microstructures characteristics of AZ-Cs are drawn based on cooling rates of these regions, and the microstructure evolution mechanism of AZ-Cs is attributed to the solute diffusion during the non-equilibrium solidification process. The hardness and toughness of AZ-Cs reach up to 21.51 ± 0.44 GPa and 5.4 ± 0.25 MPa m1/2, which far surpass these values for Al2O3/ZrO2 ceramics coatings prepared by air plasma spraying (APS). Subsequently, the Al2O3/45 mol.% ZrO2 hypereutectic powders were successfully synthesized by combustion-assisted gas atomization (CAGA) method. There is a regular spherical morphology to the powders, and the insides have typical eutectic structure. The ultra-high cooling rates supplied by CAGA greatly broadens the Al2O3/ZrO2 pseudoeutectic region. Consequently, the microstructure evolution mechanism of AZ-Cs provides a theoretical guidance to prepare high-quality eutectic powders. [ABSTRACT FROM AUTHOR]

Hollow yttrium-stabilized zirconia (YSZ) particles, which are often used to prepare high porosity coatings in industry, hit substrate at a fully molten state or semi-molten state due to the high temperature gradient of particles caused by the low thermal conductivity. Considering the hollow solid core large deformation and liquid solidification during the deposition of semi-molten hollow particles (SMHPs), a fluid-structure interaction model described by the coupled Eulerian and Lagrangian (CEL) method, is developed and validated to investigate the spreading results in thermal spraying. The empirical formula of dynamic viscosity based on the ABAQUS CEL method is proposed and verified for simulation of the liquid YSZ spreading and solidification. The compression ratio and plastic dissipation are calculated to reveal flattening and buckling phenomena of hollow solid core with different initial velocities and hollow radius. Moreover, a double-SMHP impact model is established to simulate the interaction of particle-particle-substrate, and the effect of flattening, buckling and structural self-contact on porosity is analyzed. Numerical simulation results show that hollow solid core large deformation induces instability accompanied by flattening, buckling or structural self-contact, which results in the reduction of layer porosity. [ABSTRACT FROM AUTHOR]

The 304 stainless steel coatings were applied to a 6061-T6 aluminum alloy substrate using high-velocity oxygen fuel spraying (HVOF) and air plasma spraying (APS) techniques. The objective of this study was to investigate the microstructure, hardness, tribological, and corrosion properties of the coatings produced by these two different processes. The findings revealed a clear relationship between the molten state of particles and the porosity, oxygen content, and microstructure of the stainless steel coatings. It was observed that the HVOF coating had higher quantities of austenite and martensitic, while the APS coating exhibited an increased presence of ferrite. These distinctions were directly responsible for the enhanced hardness and improved wear resistance observed in the HVOF coating. More specifically, the HVOF coating demonstrated a twofold increase in hardness (493.2 Hv0.1) compared to the APS coating. Its wear resistance was also significantly improved, with a sevenfold increase (0.36 × 10−4 mm3 N−1 m−1). Electrochemical tests were performed in a 3.5 wt.% aCl solution to assess the corrosion behavior of the coatings. The results clearly indicated that the HVOF coating provided superior corrosion protection compared to the APS coating. [ABSTRACT FROM AUTHOR]

In this study, a NiCoCrAlY + lanthanum zirconate multilayer thermal barrier coating was deposited on Inconel 738 through the thermal plasma spray technique. The coated samples subjected to hot corrosion testing at 900 °C for 240 h after coating them with 90 wt.% Na2SO4 + 5 wt.% NaCl + 5 wt.% V2O5. The corroded samples were evaluated using SEM, SED, XRD, microhardness and electrochemical study. The dominance of vanadium was observed in the form of LaVO4 phase formation at the plates on the coating surface. The as-received coating sample, sample after the electrochemical test, sample after hot corrosion and hot-corroded sample after electrochemical test were tested for hardness. A significant decrease of 23.8% in hardness was measured after the electrochemical test of the corroded sample. [ABSTRACT FROM AUTHOR]

Plasma spraying technology, known for its efficient surface enhancement capabilities, has been widely applied in aerospace, automotive manufacturing, and power generation. Ironbased coatings, due to their superior mechanical properties and wear resistance, have become important materials in these fields. However, under extreme working conditions such as high temperatures, high speeds, and heavy loads, the thermal conductivity of the coating directly affects its service life and stability. Therefore, studying the thermal conductivity of plasma-sprayed iron-based coatings is of great significance. Currently, research on the thermal properties of plasma-sprayed coatings primarily focuses on the surface thermal conductivity, neglecting the complex coupled heat transfer mechanisms within the coating. Moreover, existing research methods often rely on empirical formulas or simplified models, making it challenging to comprehensively reflect the thermal conductivity behavior under actual working conditions. This is especially true in hightemperature and high-pressure environments where the limitations of these methods are more pronounced. This paper establishes a coupled heat transfer model for plasma-sprayed iron-based coatings to explore their thermal conductivity under different working conditions. The study comprises three parts: first, the mathematical derivation of the coupled heat transfer model within the plasma-sprayed iron-based coating; second, the determination of conduction boundary conditions and the calculation of heat transfer coefficients; third, the simulation results of the thermal conductivity characteristics of the plasma-sprayed iron-based coating. This research not only fills the gaps in existing studies but also provides reliable theoretical support and data reference for practical engineering applications. [ABSTRACT FROM AUTHOR]

We prepared a catalyst-coated wire-mesh filter by thermal plasma spray method in order to develop a new type of carbon soot particulate matter (PM) removal component. The halftone plate of a SUS316 mesh was newly used as a substrate for a PM oxidation catalyst. A thermal plasma-spray method was applied to form a Ni-Pd alloy catalytic layer on the filter. As for the performace of Ni-Pd supported filter, the PM oxidation started from approximately 420°C, and the combustion at the catalytic surface took place at around 500-540°C, and finally a noncatalytic oxidation proceeded at around 650°C. The catalyst lowered a peak temperature around 110-220°C than that of only PM. Furthermore, the catalytic performance was maintained after a 5 times-repeated PM oxidation test. By the characterization of the catalyst layer, it was found that Pd particles were dispersed in a matrix of Ni and segregated on the surface and upper part of the plasma-sprayed film on the wire. The surface morphology did not change after the repeated cycle test. In this study, we found the availability of the plasma-spray catalyzed mesh filter was fabricated and as an environmental material with PM removal catalytic function. [ABSTRACT FROM AUTHOR]

Thermally sprayed ceramic coatings with carbon nanotubes (CNTs) reinforcement in three different weight percentage proportions (1%, 3%, and 5%) were investigated to evaluate their characteristics. The coatings of alumina-titania (Al2O3-3 wt% TiO2), tungsten carbide-cobalt (WC-12 wt% Co), and yttria-stabilised zirconia (ZrO2-8 wt% Y2O3) were deposited using air plasma spraying (APS). The dispersion of CNTs in the coatings' microstructure and the quality of the coatings in terms of porosity, bond strength, and corrosion resistance were investigated. The thickness of the coatings was also measured. Characterisation techniques such as optical microscopy, scanning electron microscopy, image analysis, bond strength testing, and corrosion analysis were used to study various characteristics of the coatings. The maximum porosity was found in WC-12 wt% Co and ZrO2-8 wt% Y2O3 coatings. The presence of CNTs in the coatings was confirmed through X-ray diffraction analysis. The bond strength of the WC-12 wt% Co coatings was found to be higher than that of the alumina-titania and yttria-stabilised zirconia coatings. Furthermore, the corrosion analysis revealed that alumina-titania coatings have higher corrosion resistance with a passive film when exposed to NaCl solution and better life as compared to WC-12 wt% Co coatings. [ABSTRACT FROM AUTHOR]

This work is focused on the microstructure study of nickel aluminide (Ni-5wt.%Al) deposited on an A37 steel substrate using Rietveld refinement of x-ray diffraction data. These coatings are elaborated by atmospheric plasma spray, which consists of introducing the initial feedstock material, in the form of powder, into a flame of 20,000°C temperature, melting it and spraying it on a surface to coat. The deposit was realized on two types of substrates: the first was on a non-heated substrate, and the second coating was deposited on a heated substrate at 150°C. X-ray diffraction analyses are conducted on the coating to investigate its microstructure and phases, with the Rietveld refinement technique employed to quantify the various phases present. The results showed that the nickel aluminide coatings present the formation of new phases such as Ni3Al and NiO. The surface roughness and micro-hardness values of the coatings have also been evaluated, and the mean hardness of the coating was found to be about 476 HV and 493 Hv for coatings deposited on non-heated and heated substrates, respectively. [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]

Calcia-Magnesia-Alumino Silicate (CMAS) is a form of molten siliceous residue generated at elevated temperatures within aeroengines. CMAS adheres to the surface of thermal barrier coatings (TBCs) and has the potential to cause significant damage to engine components, resulting in TBC failures. The aviation industry has long recognized CMAS as a substantial threat to aircraft engines, and this threat persists today. A substantial amount of research has been carried out, primarily focusing on gaining a fundamental understanding of the degradation mechanism of traditional TBCs manufactured using air plasma spraying (APS) and electron beam physical vapor deposition (EB-PVD) technologies after CMAS attack. A thorough understanding of why CMAS forms, its role in causing severe spallation, and how to prevent it is of significant concern both academically and industrially. This review article provides a detailed examination of the chemistry of CMAS and the resulting degradation mechanisms that the TBC may encounter throughout the aeroengine service life. This article also explores recent research, incorporating case studies, on the impact of CMAS attack on the resulting chemical and structural modifications of the ceramic topcoats. Current strategies designed to mitigate CMAS infiltration and perspectives for enhanced mitigation are discussed. [ABSTRACT FROM AUTHOR]

The Cr2O3 coating on the surface of ASTM A516 Grade 70 mild steel substrates was developed using the thermal plasma spraying process for protection against corrosion and wear. The microstructural behaviours for both coating and substrate were analysed using SEM and XRD techniques. The corrosion behaviours of the coatings and substrate in synthetic mine water with varying pH values (6, 3, and 1) were evaluated according to ASTM standards for potentiodynamic polarisation measurements. Tafel plots were drawn to determine the corrosion rates. Vickers hardness of the coatings and substrate were measured. The Cr2O3 coating exhibited cracks due to the solidification and cooling process, as well as some pores between the top and bonding layers caused by unmelted or partially melted particles. The corrosion tests revealed that a decrease in pH levels led to increased corrosion rates in both samples. The Cr2O3 coating demonstrated superior corrosion resistance, ranging from 0.036 ± 0.003 mm/year to 0.110 ± 0.004 mm/year, compared to the mild steel substrate, which ranged from 0.262 ± 0.021 mm/year to 0.336 ± 0.026 mm/year, across all pH values. Moreover, it exhibited significantly greater hardness (1260 ± 77 HV3) than the mild steel substrate (180 ± 14 HV3). The lower corrosion rates and higher hardness of Cr2O3 coating than the mild steel substrate make it a suitable coating in applications where corrosion resistance and high hardness properties are essential. [ABSTRACT FROM AUTHOR]

A silicon carbide/yttrium aluminum garnet (SiC/YAG) composite powder feedstock material developed and patented by NTNU (Norway) in 2012 has been used to produce industrial SiC thermal spray coatings since 2014. This powder is the first of its kind in the thermal spray industry. The commercial powder is produced by the agglomerated and sintered route (A&S), making it suitable mostly for High-Velocity Oxygen Fuel, but it can also be produced by the sintered and crushed (S&C) manufacturing route for Atmospheric Plasma Spray (APS). In this work, a S&C route is proposed using jaw crusher, hammer mill, and ball milling techniques. The resulting powders were then deposited using APS and were compared with the reference A&S powder. The chemistry and the microstructure of the powders and coatings were characterized using electron microscopy, x-ray diffraction, and Vickers microhardness. The S&C powders showed a density higher than the A&S powder and a blocky morphology. The S&C powders had almost no internal porosity and kept the same chemical composition as the A&S version. The coatings obtained with the S&C powders outperformed the A&S coatings, having less porosity, higher hardness, and no secondary phases. [ABSTRACT FROM AUTHOR]

Thermally sprayed ceramic coatings with varied weight percentages of carbon nanotube (CNT) reinforcement were examined. AISI 1020 steel was coated with yttria-stabilized zirconia (ZrO2 + 8% Y2O3) using the atmospheric plasma spraying (APS) method. The study examined the CNT dispersion in the coating microstructure and evaluated the porosity, bond strength, and corrosion resistance of the coating. In addition, the coating thicknesses were measured. The coatings were characterized using a variety of techniques, including optical microscopy, scanning electron microscopy, image analysis, bond strength testing, and corrosion analysis. According to the findings, adding CNTs to the coatings improved their mechanical characteristics, particularly their hardness and wear resistance. Notably, the best levels of hardness and wear resistance were seen in coatings with a 5 percent CNT reinforcement. Additionally, the coatings' corrosion resistance was enhanced by the inclusion of CNTs. The results of this work show that the mechanical and corrosion properties of thermally sprayed ceramic coatings can be successfully improved by the inclusion of CNTs. This means that these CNT-reinforced coatings have a lot of potential for a variety of applications, such as wear-resistant, corrosion-resistant, and thermal barrier coatings. [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]

NiCoCrAlY high entropy alloy (HEA) coating (47.1 wt.% Ni, 23 wt.% Co, 17 wt.% Cr, 12.5 wt.% Al, and 0.4 wt.% Y) was deposited on a stainless steel subtract by atmospheric plasma spraying (APS). The as-deposited coating was about 300 μm thickness with <1% porosity. The microstructure of the coating consisted of dispersed secondary phases/intermetallics in the solid solution. The stress–strain behaviour of this coating was investigated in micro-scale with the help of in situ micro-pillar compression. The experimental results show that yield and compressive stress in the cross-section of the coating was higher (1.27 ± 0.10 MPa and 2.19 ± 0.10 GPa, respectively) than that of the planar direction (0.85 ± 0.09 MPa and 1.20 ± 0.08 GPa, respectively). The various secondary/intermetallic phases (γ′–Ni3Al, β–NiAl) that were present in the coating microstructure hinder the lattice movement during compression, according to Orowan mechanism. In addition to that, the direction of the loading to that of the orientation of the phase/splat boundaries dictate the crack propagation architecture, which results in difference in the micro-mechanical properties. [ABSTRACT FROM AUTHOR]

Atmospheric plasma spraying (APS) is one of the most efficient processes for the preparation of yttrium oxide (Y2O3) ceramic coatings. Changing the spraying process parameters can significantly improve the microstructure and enhance the coating properties. In this study, the combination of plasma-spraying process parameters (current, spraying distance, and argon (Ar) flow) was varied by Response Surface Methodology (RSM) with the help of Minitab 19 software. Applied to the design of experiments, improvement of errors, and prediction of microstructure property results, the optimization and validation of experimental parameters for attaining the desired microstructure of Y2O3 coatings, especially porosity, was achieved. Process parameters were optimized by RSM: current 613.64 A, Ar flow rate 46.92 L/min, spray distance 15.38 cm, and optimum porosity 1.8% after optimization. Electrochemical corrosion experiments and breakdown voltage experiments revealed that the corrosion resistance and dielectric properties increased significantly as the porosity of the coatings decreased. Therefore, by optimizing the plasma-spraying process parameters, the porosity of the coatings can be significantly reduced and the corrosion resistance and dielectric properties of Y2O3 coatings can be effectively improved. [ABSTRACT FROM AUTHOR]

Hybrid plasma spraying has been proved to provide novel coating microstructures as a result of the simultaneous injection of a dry coarse powder and a liquid feedstock into the plasma jet. Such microstructure contains both large splats originating from the conventional dry powder and finely dispersed miniature splats deposited from the liquid. This approach enables preparation of coatings from virtually all materials which are conventionally processed using plasma spraying. However, incorporation of materials susceptible to volatilization or decomposition at high temperatures is still challenging even using this concept due to the high thermal energy transferred toward the feedstocks to be deposited. Hereby, an innovative approach of incorporation of thermally sensitive materials into a coating sprayed using a high-enthalpy plasma torch is proposed using so-called external feeding deposition. As a case study, three coarse-powder-based feedstocks (Al2O3, YSZ, and Cr2O3) were complemented with three suspension-based feedstocks (MoS2, WS2, and ZnS, respectively) deposited using the novel method. In all three coatings, the additional thermally sensitive materials were successfully deposited, retaining their original structure and morphology, which was confirmed using scanning electron microscopy and X-ray diffraction. [ABSTRACT FROM AUTHOR]

Achieving target coating thickness is one of the main objectives in thermal spraying. Despite this, there is a lack of measurement methods that could evaluate in situ the coating thickness with a sufficient accuracy that could be used as a robust feedback signal for online, closed-loop process control. This paper presents a novel approach for in situ spatially resolved coating thickness measurements. The measurement technique is based on a high-resolution 3D camera to capture the surface topography and include it in the thickness measurement. The technique provides results of total coating thickness with excellent accuracy when compared to the reference microscopical method. It also gives a 3D view of the coating thicknesses around the observed area as well as information about the thickness of individual coating layers. Moreover, the approach enables in situ evaluation of surface roughness, and a nondestructive estimation of coating porosity. [ABSTRACT FROM AUTHOR]

As one core component in hydrogen fuel cells and water electrolysis cells, bipolar plates (BPs) perform multiple important functions, such as separating the fuel and oxidant flow, providing mechanical support, conducting electricity and heat, connecting the cell units into a stack, etc. On the path toward commercialization, the manufacturing costs of bipolar plates have to be substantially reduced by adopting low-cost and easy-to-process metallic materials (e.g., stainless steel, aluminum or copper). However, these materials are susceptible to electrochemical corrosion under harsh operating conditions, resulting in long-term performance degradation. By means of advanced thermal spraying technologies, protective coatings can be prepared on bipolar plates so as to inhibit oxidation and corrosion. This paper reviews several typical thermal spraying technologies, including atmospheric plasma spraying (APS), vacuum plasma spraying (VPS) and high-velocity oxygen fuel (HVOF) spraying for preparing coatings of bipolar plates, particularly emphasizing the effect of spraying processes on coating effectiveness. The performance of coatings relies not only on the materials as selected or designed but also on the composition and microstructure practically obtained in the spraying process. The temperature and velocity of in-flight particles have a significant impact on coating quality; therefore, precise control over these factors is demanded. [ABSTRACT FROM AUTHOR]

Ceramic matrix composites (CMCs) have become important structural materials of aero-engines under elevated operating temperature while the abradable ceramic coatings matched with CMCs are seldom reported. In this work, the atmospheric plasma spray (APS) technique was used to fabricate and design Yb2Si2O7-based coatings with various contents of CaF2. The phase composition and microstructure of the coatings, as well as Rockwell hardness, were characterized. The wear and abradable behaviors of the coatings including friction coefficients and volume wear rates were evaluated at room temperature and 900 °C, respectively. The results show that the Rockwell hardness and friction coefficients decreased, and the volume wear rates of the coatings at room temperature significantly raised with the increase of CaF2 content. The coatings exhibited quite different behaviors at 900 °C compared with those at room temperature owing to the lubricant effect of CaF2. The morphologies of the coatings after the wear tests were characterized and the possible failure mechanisms were analyzed, and this study may provide guidelines for the application of the abradable coatings suitable for CMCs. [ABSTRACT FROM AUTHOR]

After plasma spraying, high‐velocity‐oxy‐fuel (HVOF) spraying is fast emerging as the most versatile deposition technique for thermal sprayed protective coatings. In this context, the present work aims at the deposition of a class of inter‐metallic/cermet coatings of nickel chrome boron silicium (NiCrBSi) and nickel chrome boron silicium+titanium diboride (TiB2) on 304 stainless steel substrates using high‐velocity oxy‐fuel spraying route. The cermet powder is prepared as the feedstock by mechanical mixing of the powders prior to spraying. Different coating samples are obtained by varying the flame‐to‐substrate spray distance (40 mm, 80 mm, 120 mm, 160 mm and 200 mm). These coatings are characterized in terms of their adhesion strength, deposition efficiency, thickness, and micro‐hardness by conducting tests as per the ASTM standards. The surface and interface morphologies of the deposited coatings are studied using scanning electron microscopy. The possible phases present in the coatings, and the transformation of phases during deposition have been explored by x‐ray diffraction analysis. It is found that the coatings exhibit fairly good interfacial adhesion, micro‐hardness, and thickness values that varied significantly with the spray‐distance. Further, the premixing of titanium diboride in nickel chrome boron silicium improved the mechanical and microstructural/compositional properties of the coatings. [ABSTRACT FROM AUTHOR]

The development of gas turbine technology has led to an increase in the complexity of the geometric shape of the sprayed workpiece. Consequently, it has become more difficult to maintain the perpendicularity of the spraying angle during the spraying process, thereby impacting the structure and performance of the coating. This study uses the atmospheric plasma spraying method to simultaneously spray two types of powder for the preparation of embedded micro-agglomerated particle (EMAP) coatings. The spraying process is conducted at four different angles, ranging from 90° to 30°, in order to analyze the influence of the spray angle on the particle deposition and coating performance. The experimental results demonstrate that the relative deposition efficiency, hardness, and elastic modulus of the EMAP coatings decreased as the spray angle decreased. The porosity exhibited a reduction when the spraying angle dropped from 90° to 50°, followed by a significant rise at 30°. The greatest relative amount of second phase particles embedded in the coating appeared at a spraying angle of 90°, amounting to 10.8%. The smallest amount was found at a spraying angle of 30°, with a relative quantity of 2.2%. Furthermore, the molten droplets of the first phase matrix powder underwent extension and fragmentation along the angular direction at low angles. At an angle of 90°, the maximum average thermal shock life was 40.6 cycles, with the best stability of thermal shock life. The decrease in the spraying angle resulted in a deterioration in both the thermal shock life and its stability. [ABSTRACT FROM AUTHOR]

To improve the sliding wear resistance of plasma sprayed Mo coating, Mo–SiC and MoO 3 –Al–SiC composite powders were used to prepare Mo composite coatings by plasma spraying. The results show that the introduction of SiC improved the mechanical properties and sliding wear resistance of plasma sprayed Mo coating. The reactivity of Mo and SiC was low during plasma spraying Mo–SiC composite powder. The thermite reaction for MoO 3 and Al was not conducive to the densification of the composite coating prepared by MoO 3 –Al–SiC composite powder, but improved the reactivity of in-situ generated Mo and SiC, and the Nowotny phase Mo 4.8 Si 3 C 0.6 was observed in the coating. The coating prepared by Mo–SiC composite powder displayed better mechanical properties and sliding wear resistance than that of the coating prepared by plasma spraying MoO 3 –Al–SiC composite powder. The coating obtained by Mo–SiC composite powder revealed a combination of adhesive wear, abrasive wear and oxidation wear. [ABSTRACT FROM AUTHOR]

Deposition characteristics determine the effectiveness of plasma spraying. In this paper, the different deposition mechanisms related to the spraying of Cr2O3, Al2O3, and Al2O3-40%TiO2 onto aluminum alloy substrates are analyzed; in this manner, we investigate the coating morphology as well as the temperature and stress fields within coatings made of these particles. When spraying is performed, the sputtering phenomenon of particles on the substrate and the stress within the coating gradually disappears as the substrate temperature and stress increase when the external stress reaches the order of 40 MPa from zero and the temperature reaches 400 K. It is found that the thermal effects of the Al2O3 coating on the substrate were the largest of the materials investigated here, and the thermal effects of the Cr2O3 and Al2O3-40%TiO2 coatings were relatively small. The multiparticle deposition model was found to be consistent with the experimental particle morphology obtained via metallographic and SEM methods; the simulations were thus found to accurately represent the state of and mechanisms behind the deposition processes. By comparing the different deposition behaviors of different particles on the aluminum alloy substrate, the deposition mechanism can be further investigated by guiding the actual coating. [ABSTRACT FROM AUTHOR]

The effect mechanism of microstructure and environmental conditions on the dielectric properties of plasma-sprayed Al 2 O 3 insulating coatings was systematically investigated in this study. Two kinds of Al 2 O 3 powders with different particle sizes were used to deposit the coatings under the same spraying parameters. The microstructures of the coatings (including porosity, pore size, crack density, and phase composition) were analyzed using scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and X-ray diffraction (XRD). The dielectric properties (including breakdown strength, resistivity, dielectric constant, dielectric loss, and complex impedance) were characterized by a two-electrode measurement cell. The results indicated that the coating deposited with the larger-sized powder (D 50 =45.8 μm) exhibited higher porosity, α-Al 2 O 3 content, and connected crack density, than the coating with the other kinder of powder (D 50 =22 μm). The DC and AC breakdown strengths were found to be related to the porosity of the coatings and the partial discharge in the pores results in the eventual breakdown. The resistivity of the coatings decreased significantly with increasing humidity due to the moisture adsorbed on the pores and cracks. In high-humidity environments, the water molecule enhanced space charge polarization (WESCP), as the main polarization mode, contributed to the dramatic increase of the dielectric constant and dielectric loss. Moreover, the complex impedance and phase angle showed frequency-dependent changes in different environments, suggesting a combined effect of humidity and temperature on the polarization and conductance of coatings. The obtained results of this study could pave the way for the design and application of high-performance plasma-sprayed insulating coatings. [Display omitted] [ABSTRACT FROM AUTHOR]