Plasma Spraying Method Research Articles

Cyclic oxidation and water vapor corrosion behaviors of multi-layer environmental barrier coatings with HfO2-Si bond coat for SiCf/SiC

A novel multi-layer HfO2-Si/YbSi1.5/Yb2SiO5/LaMgAl11O19 environmental barrier coatings (EBCs) was prepared using atmospheric plasma spraying method to restrain spallation failure and improve lifetimes of coating. The thermal cycling behaviors of SiCf/SiC completely covered with multi-layer EBCs were comparatively investigated at 1300 °C and 1350 °C in air. Meanwhile the water vapor corrosion behavior of coated sample was also investigated at 1300 °C for 100 h in 90% H2O-10% O2 steam. The coating at 1300 °C showed better thermal shock resistance than the coating at 1350 °C, due to the increase of tensile stresses at 1350 °C. The coating showed different forms of crack penetration due to the influence of thermal cycling temperature and water vapor. The formation of HfSiO4 phase thanks to solid-state reaction between HfO2 and SiO2 alleviate the β→α-cristobalite phase change and avoid the crack initiation. However, the thermal mismatch stress was contributed to the spallation of coating along the surface of the SiCf/SiC substrate.

Laser Surface Alloying of Sintered Stainless Steel.

A characteristic feature of sintered stainless steel (SSS) is its porosity. Porosity results in a lower density of steel, making attractive components for producing lightweight structures and materials used in industry (e.g., the automotive industry or aerospace). Scientists also observe that porosity adversely affects steel’s properties, especially its strength properties. One of the proposals for improving the discussed properties is the use of surface treatment of sintered stainless steels, e.g., with the use of concentrated energy sources such as plasma beams or laser beams. However, this proposal is an incidental subject of research, which is not justified from the point of view of the obtained research results presented by a few research groups. In this study, the surface modification (surface treatment) of sintered stainless steel was presented. The authors proposed the use of two surface treatments in order to compare them and obtain the best results. The first treatment was the deposit of Cr3C2–NiCr coatings on SSS surfaces using the atmospheric plasma spraying (APS) method. The second treatment was to create surface layers on SSSs by laser alloying the surface with a CO2 laser. Due to high precision and ease of automation, the most common methods in surface alloying treatment are laser technologies. This research’s main aim was to analyze the microstructure and strength properties of the SSS surface layer. The research confirms that applying the Cr3C2–NiCr coating and modifying the surface layer through the laser alloying method improves the mechanical properties of SSSs.

Optimization of plasma spray process variables to attain the minimum porosity and maximum hardness of the LZ/YSZ thermal barrier coatings utilizing the response surface approach

Lanthanum zirconate (LZ) has emerged as a novel thermal barrier coating (TBC) material because of its higher temperature phase stability, and low sintering ability than the current standard yttria-stabilized zirconia (YSZ). In order to combine the advantages, LZ and YSZ feedstock powders are blended with predetermined weight ratios (50:50) as composite coatings. The leading issue in developing the composite coating using the atmospheric plasma spray method (APS) is finding the optimum range of input parameters to attain the desired coating properties. This issue can be resolved by developing empirical relations to find the porosity and microhardness of the coating by the atmospheric plasma spray method (APS). Spray parameters such as input power, spray distance, and powder feed rate are vital in determining the coating quality. Three variables and five levels of central composite rotatable design (CCD) to reduce the overall run of the experiment were utilized in the research. The empirical relations were predicted to find the porosity and microhardness of the specimens with APS process parameters, and the empirical relations were examined through ANOVA. Optimizing the plasma spray parameters was done using response surface methodology (RSM), which provides the minimum porosity and maximum hardness. It is validated using surface response graphs, contour plots, and overlay plots. As a result, the input power has the greatest impact on the coating properties among the three variables, and the standoff distance and powder feed rate are the subsequent important spray parameters.

Ca-Mn co-doping LaCrO3 coating with high emissivity and good mechanical property for enhancing high-temperature radiant heat dissipation

Two techniques, including spray drying and electrostatic spray, were applied to produce feedstocks for preparing Ca-Mn co-doping LaCrO3 ceramic coatings with two different structures on Ni-based alloy by the atmospheric plasma spraying method. The results show that coating from feedstocks produced by spray drying exhibits lower roughness and porosity than the coating from feedstocks produced by electrostatic spray due to the full melting of smaller feedstocks. Higher proportion of melting zones is beneficial to enhance the ratio of hardness to modulus to improve wear resistance. The emissivity of the coatings with roughness from 0.65 µm to 4.6 µm is all above 0.9 in the waveband of 1–14 µm at room temperature. What’s more, structure-dependent emissivity is affected by surface roughness and pore size due to the infrared scattering. The temperature-dependent thermal infrared emissivity at 1–14 µm decreases with the increasing temperature, and is still above 0.67 at 1200 °C.

Residual stress evolution of 8YSZ:Eu coating during thermal cycling studied by Eu3+ photoluminescence piezo-spectroscopy

Thermal barrier coatings (TBCs) are widely used to protect high temperature structure parts against oxidation and corrosion. The failure mechanism study of TBCs is very important and the stress evolution is core content of failure mechanism research. In this work, a 8YSZ:Eu coating was produced via atmospheric plasma spraying (APS) method. Thermal cycling tests was carried out at 1300 ℃. The residual stress evolution of the coating was detected by a Eu 3+ photoluminescence piezo-spectroscopy based on the relationship between stress and the peak position of 5 D 0 → 7 F 2 transition of Eu 3+ ions. The failure mechanism of the 8YSZ:Eu coating was also studied. The as-sprayed 8YSZ:Eu coating contains metastable t ´ -ZrO 2 and amorphous structure. The stress distribution is inhomogeneous with both compressive stress and tensile stress. After 1000 thermal cycles, the initial compressive stress changed to tensile stress due to the thermal expansion coefficients (TEC) mismatch and irreversible plastic deformation during thermal cycling. With thermal cycling going on, the compressive stress appeared again and the averaged tensile stress decreased due to the volume expansion caused by phase transformation of the t ´ -ZrO 2 to m-ZrO 2 and the formation of cracks. Formation of the thermally grown oxide (TGO), phase transformation, thermal expansion mismatch are factors for the coating failure. • A Eu 3+ photoluminescence piezo-spectroscopy was used to measure the residual stress. • The residual stress distribution and evolution of the 8YSZ:Eu layer during thermal cycling was studied. • A 8YSZ:Eu coating was prepared by atmospheric plasma spraying and thermal cycling behavior was studied.

Use of La2O3 with 8YSZ as thermal barrier coating and its effect on thermal cycle behavior, microstructure, mechanical properties and performance of diesel engine operated by hydrogen-algae biodiesel blend

In this present work, the effect of lanthanum oxides (La2O3) on the thermal cycle behavior of TBC coatings and mechanical properties such as adhesion strength and microhardness of 8% Yttria Stabilized Zirconia (8YSZ) TBCs were investigated. CoNiCrAlY and aluminium alloy (Al–13%Si) were used as bond coat and substrate materials. 8YSZ and different wt % of La2O3 (10, 20, and 30%) top coatings were applied using the atmospheric plasma spray (APS) method. The thermal cycling test for TBC coated samples were conducted at 800 °C in the electric furnace. The XRD pattern shows that the La2O3 doped 8YSZ material transformed to cubic pyrochloric structured La2Zr2O7 during thermal cycling. Further, the Taguchi-based grey relation analysis (GRA) method was applied to optimize the TBC coating parameters to achieve better mechanical properties such as adhesion strength and microhardness. And the optimized La2O3/8YSZ TBC coating was coated on CRDI engine combustion chamber components. The engine was tested with microalgae biodiesel and hydrogen, and the results were promising for the TBC-coated engine. The engine performance increased while using La2O3/8YSZ coated components, and the emissions from engine exhaust gas such as CO, HC, and smoke reduced considerably. It was found that there was no separation crack and spallation of the coating layer in the microstructure. Ultimately, the microstructural analysis of the optimized TBC coated piston sample after 50 h of running in the diesel engine confirmed that the developed coating had a superior thermal insulation effect and longer life.

Formation of composite coatings by the method of supersonic plasma spraying of powders based on TiAl intermetallic with non-metallic refractory compounds SiC and Si<sub>3</sub>N<sub>4</sub>

The Paton Welding Journal, 2022, №06. International Scientific-Technical and Production Journal «The Paton Welding Journal» «The Paton Welding Journal» has been published monthly since 2000 in English, ISSN 0957-798X. «The Paton Welding Journal» is a cover-to-cover English translation of the «Avtomaticheskaya Svarka» (Automatic Welding) journal. The «Avtomaticheskaya Svarka» journal has been published monthly since 1948 in Russian, ISSN 005-111X.

Synthesis of spherical mullite/Yb2SiO5 composite EBC powder by using mechanical alloying and spray dry processes

Abstract Environmental barrier coatings (EBCs) have been widely used as protective layers to protect the surface of ceramic components from water vapor degradation and hot corrosion at operating temperature. In this study, ytterbium monosilicate (Yb2SiO5) and mullite (3Al2O3·2SiO2) powders were synthesized by mechanical alloying to be considered as a new environmental barrier coating. The composite powder was granulated by the spray dryer process and deposited on SiC reinforced by carbon fibers (SiC/Cf) substrate using the atmospheric plasma spray method. Phases in the synthesized composite powders and the deposited EBC were identified using X-ray diffraction. A field emission scanning electron microscope equipped with energy dispersive X-ray spectroscopy was utilized to study the powder morphology and coating microstructure. After the spray dry processing, the powders exhibited a spherical morphology and good-flowability with a mean particle size of 20–40 µm. The coating thickness was measured to be between 100 and 150 μm. In addition, the results of nanoindentation testing exhibited a hardness of about 8 GPa and an elastic modulus of about 111 GPa for the deposited coatings.

SURFACE CHARACTERIZATION OF ARBOBLEND V2 NATURE COATED WITH CERAMIC MICRO PARTICLES

The paper aims to investigate the behavior of Arboblend V2 Nature biopolymer samples covered with three ceramic powders, Amdry 6420 (Cr2O3), Metco 143 (ZrO2 18TiO2 10Y2O3) and Metco 136F (Cr2O3-xSiO2-yTiO2). The coated samples were obtained by injection molding, and the micropowder deposition was achieved by using the Atmospheric Plasma Spray (APS) method, with varied thickness layers. The present study will describe the results for nine, seven and five-layer deposition. It was observed that with the increase of the number of deposited layers the surface quality and mechanical/thermal characteristics such as wear and hardness are also increased. The followed determinations were conducted: the adhesion strength and hardness on a microscopic scale by micro-indentation. The samples’ crystalline structure as well as the presence of the Cr2O3 compound significantly influenced the micro-indentation and scratch analysis responses. The novelty of this study is given by itself the coating of the Arboblend V2 Nature biopolymer (as base material), with ceramic microparticles as the micropowder coating material. Following the under-taken study, the increase in the mechanica and tribological characteristics of the samples recommend all three coated biopolymer samples as suitable for operating in harsh conditions, such as the automotive industry, in order to replace plastic materials.

Thermal cycling behavior of Si/Yb2SiO5/LaMgAl11O19 TEBCs coated SiCf/SiC composites under burner rig tests

In order to promote the thermal cycling behavior of SiCf/SiC composites at high-speed gas scour and high-temperature environment, we have prepared three-layer Si/Yb2SiO5/LaMgAl11O19 TEBCs onto the surface of SiCf/SiC composites using atmospheric plasma spraying (APS) method. Burner rig tests were performed to evaluate the thermal cycling behavior of TEBCs. Results show that after being tested in high-temperature and high-speed burner flame, only a small number of TEBCs cracked and peeled in the external area of TEBCs caused by the thermal stress and the corrosion of water vapor, but TEBCs did not crack and spall in the center area. The failure mechanism of TEBCs was investigated. Microstructure characterization indicated that the penetrating cracks in TEBCs provided the channel for oxygen and water vapor diffusion to SiCf/SiC composites leading to the severe corrosion of substrate.

Experimental Examination on Performance and Emission of a Coated Diesel Engine Fueled with Diesel and Pre-Heated Coriander Oil Blends

Abstract The aim of the study is to determine the effects of the preheated coriander seed oil, used as fuel, on the performance and the emission characteristics of the ceramic coated single-cylinder diesel engine. In this study, the piston, exhaust, and inlet valve of a single-cylinder air-cooled diesel engine were coated with Cr3C2 at 300 µm thickness. Pure coriander oil was mixed with diesel fuel volumetrically at the rates of 30% and 50%. The plasma spray method was used as the coating method. It was determined that the preheating process provided a more suitable fuel flow, decreased the viscosity of the coriander oil and also the coating process decreased CO, soot and HC emissions but increased NOx, thermal efficiency, and EGT.

Effect on wear properties of coating the surface of 904L super austenitic stainless steel by APS with white/grey Al2O3

ABSTRACT Although stainless steels are widely used in industry due to their high corrosion resistance, low surface hardness is considered a disadvantage when exposed to repeated loads. In this study, the effects of coating the surfaces of 904L super austenitic stainless steel by the Atmospheric Plasma Spray (APS) method using grey and white alumina on microstructural and tribological properties were investigated. According to the results of the examination, a flat homogeneous coating layer was obtained. In the coatings made with both materials, α-Al2O3 and γ-Al2O3 phases were formed on the surface. Although the coating layer thickness is higher in grey alumina, the hardness is higher in coatings made with white alumina, and the surface hardness has increased by 2–3 times. According to the wear tests, it was determined that the wear resistance of white alumina was higher and the wear resistance of the alumina coating increased 3–4 times.

Investigation of nanoporous silicon on the frontal surface of solar cells by mass spectroscopy

When using nanoporous silicon (nano-PSi) as a texture and anti-reflective coating, the nanoporous layer is formed directly on the silicon surface of the front layer of solar cells (SC). Along with blooming, it must also provide passivation of the SC surface. Research in this area has shown that the passivating properties of PSi are insufficient to minimize surface recombination. Partial improvement of the passivating properties of nano-PSi was achieved by thermal and anodic oxidation, as well as by plasma spraying methods. However, none of these methods were allowed to achieve the required level of surface passivation and its stabilization over time. A more effective method of improving the passivating properties of PSi is electrochemical hydrogenation in hydrogen-enriched electrolytes. Here we used mass spectroscopy to study the frontal surface of the SC. We also studied the surface appearance of multicrystalline silicon samples before and after hydrogenation in hydrogen and in an electrolyte based on hydrofluoric acid, both in the spectra of secondary ions and in the image of the distribution of elements on the surface.

Plasma sprayed fluoride and zinc doped hydroxyapatite coated titanium for load-bearing implants

Titanium (Ti) alloys show excellent fatigue and corrosion resistance, high strength to weight ratio, and no toxicity; however, poor osseointegration ability of Ti may lead to implant loosening in vivo. Plasma spraying of hydroxyapatite [HA, Ca10 (PO4)6 (OH)2] coating on Ti surfaces is commercially used to enhance osseointegration and the long-term stability of these implants. The biological properties of HA can be improved with the addition of both cationic and anionic dopants, such as zinc ions (Zn2+) and fluoride (F−). However, the hygroscopic nature of fluoride restricts its utilization in the radiofrequency (RF) plasma spray process. In addition, the amount of doping needs to be optimized to ensure cytocompatibility. We have fabricated zinc and fluoride doped HA-coated Ti6Al4V (Ti64) to mitigate these challenges using compositional and parametric optimizations. The RF induction plasma spraying method is utilized to prepare the coatings. Multiple parametric optimizations with amplitude and frequency during the processing result in coating thicknesses between 80 and 145 μm. No adverse effects on the adhesion properties of the coating are noticed because of doping. The antibacterial efficacy of each composition is tested against S. aureus for 24, 48, and 72 h, and showed that the addition of zinc oxide and calcium fluoride to HA leads to nearly 70 % higher antibacterial efficacy than pure HA-coated samples. The addition of osteogenic Zn2+and F− leads to 1.5 times higher osteoblast viability for the doped samples than pure HA-coated samples after 7-days of cell culture. Zn2+ and F− doped HA-coated Ti64 with simultaneous improvements in anti-bacterial efficacy and in vitro biocompatibility can find application in load-bearing implants, particularly in revision surgeries and immune-compromised patients.

Corrosion behaviour of nickel based abradable coating used in aero engines

The corrosion potential of abradable nickel based coating used for aero engine components (for sealing and clearance control in compressor of aero engines) was explored and the effect of acid rain was observed for varied length of time. Coating plays an important role in aero engine manufacturing industry as it provides surface protection against corrosion, erosion, friction and wear when subjected to harsh conditions viz., high temperature and corrosive environment during service period. The coating deposition was done by using thermal plasma spray method. Porosity was observed to be high at critical plasma spray parameter (CPSP). Phase transformation and interlayer oxide formation were also observed during plasma spray coating. A comparative study was established between acid rain treated and untreated samples by evaluating the corrosion resistance potential, microstructural characterization, composition and phase analysis of coatings of treated samples using Scanning electron microscopy, X-ray diffraction and EDS. The weight gain of coating was also evident after acid rain treatment of up to ten weeks of immersion.

Phase transformation and thermal conductivity of the APS Y2O3 doped HfO2 coating with hybrid structure

Hafnia-based materials are very promising to serve as thermal protecting coatings at temperature above 1200 °C. In this work, two kinds of 8 mol% Y2O3 stabilized HfO2 ceramic coatings (YSH-SN and YSH-MX) with conventional and hybrid structures were prepared by air plasma spray (APS) method. The microstructure, thermal conductivity and the mechanical properties of the coatings before and after thermal exposure at 1300 °C were compared in detail. Results show that the as-sprayed YSH-MX has a hybrid laminated structure of monoclinic HfO2 and cubicY2O3 splats, and transforms to monoclinic HfO2 and cubic YSH after thermal exposure, while the YSH-SN is composed of major tetragonal YSH phase and transforms to monoclinic HfO2 and cubic YSH afterward. Thermal conductivities at ultra-high temperature (1600 °C) before and after thermal exposure for those two coatings are close, and the fracture toughness in the direction parallel to the interface exceeds 2.1 MPa m0.5. The YSH-MX coating with a hybrid structure provides insights to conveniently prepare gradient coating or other coatings with complex structures.

Effect of irregular microcracks on the hot corrosion behavior and thermal shock resistance of YSZ thermal barrier coatings

The durability and service performance of thermal barrier coatings (TBCs) is influenced by its microstructure. One type of yttria stabilized zirconia coating containing irregular microcracks (mc-YSZ) was prepared by atmospheric plasma spraying (APS) method in this study, and the differences in hot corrosion behavior and thermal shock resistance between the conventional YSZ coating and the mc-YSZ coating were investigated. Results showed that the presence of irregular microcracks facilitated the penetration of corrosive salt (V2O5 and Na2SO4) and accelerated the hot corrosion reaction. The deflection effect of irregular microcracks in the early stage of hot corrosion could suppress the propagation of cracks generated by corrosion; but irregular microcracks would merge with corrosion cracks in the later stages of corrosion and aggravate the failure of the coatings. Thermal shock tests showed no significant difference of the thermal shock lifetime between YSZ coating and mc-YSZ coating, which proved that this irregular microcrack could not effectively improve the strain tolerance. The present study provides a reference for the structure design of thermal barrier coatings: when designing the structure of the coating, the appearance of that irregular microcracks should be avoided.

Plasma processing of Fe-P/rGO powder for making robust wear resistance and anticorrosion coating over mild steel

Phosphating is a widely used metal pre-treatment process due to its ability to improvise pitting corrosion resistance, wear-resistance, and adherence properties. In the present investigation, we report the manufacturing of spray grade powder of Fe-P metal ingot by mechanical hammering, milling and sieving process. The Fe-P powder and its blending with reduced graphene oxide (rGO) (2 and 4 vol%) were successfully coated over mild steel by the thermal plasma spray method for the first time. Successful retention of rGO was observed even after thermal plasma spraying of Fe-P/rGO (2 vol% and 4 vol%), which was challenging and yet to be reported. The morphological investigation of the top-coat layer and cross-section was analysed using a field emission scanning electron microscope (FESEM). The presence of G, D and 2D bands at 1580 cm−1, 1350 cm−1, and 2700 cm−1, respectively in the Raman spectra were the straightforward demonstration of the retention of rGO. Hardness and air-jet erosion tests were performed to evaluate mechanical properties in view of exploring commercial applications of such coatings. We found that Fe-P-rGO composite coatings exhibited improved hardness, erosion, and corrosion resistance properties with increasing reduced graphene oxide content.

Study of high-temperature behavior of a heat-protective coating of zirconium dioxide by laser heating

When studying the high-temperature behavior of the heat-protective coating of zirconium dioxide, the method of laser heating has been tested. The coating was applied by the method of high-energy plasma spraying on the intermetallic sublayer of the Ni–Co–Cr–Al–Y system made of a powder material of the composition (ZrO2 + 7% Y2O3) of spherical morphology.The aim of this work was to study the processes of structural-phase transformations, melting and crystallization occurring in a ceramic coating material under the action of a single laser pulse with a duration of 14 ms with different energies (5, 10, 15, and 20 J). It was found that after spraying, the coating in the initial state has a two-phase composition (T-ZrO2 + K-ZrO2), and a layered microstructure with a columnar structure of zirconium dioxide grains. Laser heating with a pulse energy of 5 J stimulates the phase transformation T-ZrO2 → K-ZrO2, the appearance of porosity and microcracks. With an increase in the pulse energy to 10 and 15 J, the processes of melting and ultrafast crystallization, accompanied by grain refinement, intensively occur on the coating surface. According to the theoretical estimates, the reflow processes affect surface layers with a thickness of 2.2 to 6.6 μm, and phase transformations take place at a depth of ~11 μm. With an increase in the laser pulse energy to E = 20 J, the process of destruction of the coating was initiated by the mechanism of cracking with delamination of fragments of the surface layer 5–10 μm thick.The laser heating method is recommended as an express diagnostics for comparative tests of the heat resistance of ceramic coatings obtained by different methods and from different starting materials.

Synthesis of low-cost Ti4O7 membrane electrode for electrooxidation of tetracycline under flow-through conditions: Performance, kinetics and mechanism

The high cost of anode material and the limitation of liquid-mass transfer on anode surface in electrochemical advanced oxidation processes always restrict the removal efficiency of organics. To overcome the limitations, this study synthesized a low-cost Ti4O7 membrane electrode by simple sol-gel method, and developed a flow-through electrooxidation system based on Ti4O7 membrane electrode. The membrane electrode presented high crystallinity, high specific surface area (10.18 m2/g), concentrated pore sizes distribution (0.1–1 µm), and high oxygen evolution potential (2.2 V vs. SHE). Furthermore, compared with stirring conditions, the flow-through conditions could enhance the liquid-mass transfer on anode surface, resulting in a high tetracycline degradation efficiency (97.24%) and a low energy consumption (0.18 kWh/gDOC). High degradation rates of tetracycline (more than 95%) were both observed with the initial tetracycline concentration ranged from 10 to 50 mg/L. The increase of pipeline pressure and current density had positive influence on tetracycline degradation. Hydroxyl radicals and sulfate radicals produced on the electrode surface are the main oxidants for tetracycline degradation. The degradation pathway of tetracycline included oxygenation, hydroxylation, demethylation, decarbonylation, ring-open, and C-N bond cleavage. Compared with materials prepared by conventional hot pressing and plasma spraying method, this simply synthesized Ti4O7 membrane electrode exhibited efficient oxidation capability and competitive electric cost for contaminants degradation, demonstrating its practicability, feasibility, and facilitation for the potential application.