Plasma Spraying Research Articles

Adapting high-speed indentation mapping for investigating microstructure-property correlations in chromium carbide-nickel alloy coatings: Challenges and solutions

This study investigates the microstructural and mechanical characteristics of chromium carbide‑nickel rich alloy coatings produced through laser cladding, detonation spraying, and plasma spraying techniques. While all three processing techniques used the same feedstock powder, each method yields coatings with unique microstructures encompassing varying compositions and length scales. Employing Field Emission Scanning Electron Microscopy (FE-SEM) in combination with Energy Dispersive Spectroscopy (EDS) and nanoindentation mapping, local microstructure and mechanical properties were assessed at the micrometre length scale. Laser-clad coatings exhibit a typical metal matrix composite microstructure with high carbide content, distinct (MoNb)C2 phases, and Fe in the metallic matrix, while the thermal sprayed coatings showed carbides of varying sizes and metallic matrix with varying degrees of chromium dissolved in it. The instrumented indentation technique helped precisely record the microstructural features in all the coatings. Chromium carbide consistently emerges as the hardest phase across all coatings, with variations in metallic matrix hardness. Higher matrix hardness in thermal sprayed coatings correlates with increased Cr content, attributed to extended solid solubility of Cr and the presence of Mo and Nb. Energy dispersive spectroscopy and transmission electron microscopy provided clearer insight into the microstructure. This study highlights a direct one-to-one correlation between microstructure and mechanical properties mapped using instrumented indentation techniques in chromium carbide‑nickel rich coatings across different deposition methods.

Formation mechanism of Al-O intergranular amorphous phase toughened nanoscale ZrB2-ZrC composite coating synthesized by reactive plasma spraying

A new nanostructured ZrB2-ZrC composite coating with ZrB2-ZrC nanoscale eutectic and ZrB2+Amorphous microstructure was synthesized in situ by plasma spraying Zr-B4C-Al composite powder. The thermal analysis, quenching experiments and microstructure characterization were investigated and the formation mechanism of the bimodal in-situ microstructure was revealed. Al contributed to the liquid phase separation of molten droplets, which is the key to forming ZrB2+Amorphous microstructure. The formation of coating followed reaction-melting-liquid separation-deposition and solidification mechanism. The nanostructured ZrB2-ZrC composite coating with Al-O intergranular amorphous phase has excellent mechanical properties. The uniform nano-grains improved the hardness and the toughness of the ZrB2-ZrC eutectic. The ZrB2+Al-O amorphous microstructure obtained high toughness and the toughening mechanism was the crack deflection and crack branching caused by intergranular Al-O amorphous phase.

The Influence of Injection Mode and Spray Distance on Wear Resistance of Al2O3+13 wt.% TiO2 coatings

Abstract Atmospheric plasma spraying (APS) allows deposition of ceramic coatings on metallic substrate, significantly increasing the wear resistance of the component. Coating’s microstructure and consequently its properties, depend on heat treatment of the feedstock particles. This property can be controlled by process parameters, especially electric power and spray distance. On the other hand, some plasma torches allow introducing another variable, an injection mode, which could be realized in external or in internal way. In the presented research, wear resistance of Al2O3+13 wt.% TiO2 coatings deposited under various values of spray distance and different injection modes were examined using ASTM G-99 procedure. The impact of spraying parameters on the coating’s microstructure was established and connected to the functional properties of the manufactured deposits. Observed differences indicated influence of injection mode and spray distance value. Coatings deposited with internal feedstock injection exhibit lower porosity and slightly higher hardness than these made with external injection mode. In terms of wear resistance for both spray distance the wear factor was lower for internal injection system. Obtained results confirmed assumed thesis, that internal injection mode improves heat treatment and consequently ameliorate wear performance of plasma sprayed alumina-titania coatings.

Integrating TiNx to Fe-based amorphous coating by reactive plasma spray for ameliorating multi-scale mechanical behavior and corrosion-abrasion resistance

Ocean engineering components are subjected to intense corrosion and abrasion. To address these challenges, the Fe-based amorphous composite coating was engineered for compatibility with these harsh conditions. The Fe-based amorphous composite coating, incorporating TiNx, demonstrated improved nanomechanical properties, offering enhanced resistance against external forces. The integration of TiNx acted as a structural backbone, limiting crack propagation within the amorphous matrix. Although the corrosion resistance of this composite coating was slightly reduced, it demonstrated improved durability subjected to hydraulic machinery corrosion abrasion working condition. Notably, under conditions of higher tribological pair speeds and increased sand concentrations, this composite coating exhibited significantly lower weight loss increase and reduced wear rates escalation compared to coatings made entirely from Fe-based amorphous material. Moreover, the composite coating exhibited diminished susceptibility to erosion damage, with reduced size and severity of erosion craters. These underlying mechanisms are thoroughly discussed in the paper.

The influence of heat treatment on AlSi-polymer abradable coating

Abstract Abradable coatings, as one of the most important technologies for aero and industry gas turbine engines, have an extremely significant influence on engine performance. The macro-hardness of AlSi-Polyester for low-pressure compressor and as-sprayed coating degradation mechanism has been investigated by heat treatment process in imitation service condition. SEM (Scanning Electron Microscope) and OM (Optical Microscope) were used to observe the morphology of powder and coating microstructure in cross-section, respectively. Rockwell hardness tester was used to measure the macrohardness of coatings before and after heat treatment. It shows that AlSi-Polyester powder has an approximately spherical shape and uniform microstructure with alloy phase and polyester phase distribution in the coating prepared by air plasma spraying. Oxidation of the alloy phase and reduced polyester, as well as macrohardness in the as-sprayed coating, occur after the heat treatment process.

The Effect of Plasma Spraying Technological Modes on the Strength of Coating Adhesion onto a Screw-Shaped Substrate

The Effect of Plasma Spraying Technological Modes on the Strength of Coating Adhesion onto a Screw-Shaped Substrate

Effect of TiO2 content on the thermal control properties of Al2O3-xTiO2 composite coatings prepared by supersonic plasma spraying technology

The main challenge faced by spacecraft is the large temperature difference in its operating environment. Thermal control coatings prepared on spacecraft and instrument surfaces are currently the most efficient ways for heat dissipation and control. In this work, Al2O3-xTiO2 composite coatings with different TiO2 contents were prepared on 7075-Al alloy substrate by supersonic plasma spraying technology. The microstructure, phase composition, mechanical properties, thermal control properties, and corrosion resistances of the coatings were investigated. The raw stock feeds were mainly composed of α-Al2O3 and anatase TiO2, but the coatings were mainly γ-Al2O3 and rutile TiO2. The average Vickers microhardness of the coatings decreased from 1198.9 to 810.4 HV0.2 with the increase of TiO2 contents, but the elastic modulus increased from 158.5 to 244.3 GPa. The thermal control properties of the coatings were promoted with the growth of TiO2 contents, and the absorptance increased from 27.1 to 89.2% with the emittance from 83.7 to 86.5%. The corrosion potential and corrosion resistance of the coating gradually increased with TiO2 content due to its gradually improved hydrophobicity. This work broadens the application boundary of Al2O3-xTiO2 composite coating and provides an innovative idea for material selection of thermal control coatings.

EXPERIMENTAL ANALYSIS AND OPTIMIZATION OF PLASMA SPRAY PARAMETERS ON POROSITY AND CORROSION WEAR OF Cr3C2/8YSZ COMPOSITE-COATED AUSTENITIC STAINLESS STEEL

EXPERIMENTAL ANALYSIS AND OPTIMIZATION OF PLASMA SPRAY PARAMETERS ON POROSITY AND CORROSION WEAR OF Cr₃C₂/8YSZ COMPOSITE-COATED AUSTENITIC STAINLESS STEEL

Investigation of the cooling hole blockage induced by different thermal spray TBC deposition processes

High-temperature turbine airfoils and combustion chamber walls in jet engines require sufficient cooling via cooling holes and thermal barrier coating systems (TBCs) to protect them from hot combustion gases. As the demand for greater efficiency and higher firing temperatures in jet engines increases, there is a corresponding need for more advanced film cooling methods, such as the use of more complex hole geometries. The use of Additive Layer Manufacturing (ALM) techniques allows the production of such intricate cooling holes, enhancing the flow of cooling air onto component surfaces. Conventional TBC deposition techniques, for example Atmospheric Plasma Spraying (APS) or Electron Beam Physical Vapor Deposition (EB-PVD), often lead to partial or complete blockage of cooling holes. This study compares the blockage of TBCs deposited on conventionally-sheet alloys with standard cooling holes and ALM alloys with more complex cooling holes using APS as a baseline process. Additionally, alternative plasma spray deposition technologies such as Suspension Plasma Spraying (SPS) and Plasma Spray-Physical Vapor Deposition (PS-PVD) were explored. The aim was to determine the effectiveness of these processes in preventing blockage compared to the traditional APS process. The experimental results showed that the formation of the coating, whether originating from splats or from the vapor phase, the feedstock particle size, and the cooling hole geometry can all affect the blockage. It was demonstrated that PS-PVD, with its vapor-induced deposition, is highly effective in minimizing blockage, regardless of the cooling hole geometry.

Corrosion Resistance and Wear Response of Plasma Spray Nano-Ceramic Composite Coatings on AZ91D Alloy

Corrosion Resistance and Wear Response of Plasma Spray Nano-Ceramic Composite Coatings on AZ91D Alloy

Effect on Ti/Mg isothermal oxidation of refinement microstructure and tribological behaviour of pure aluminium alloy by plasma spray coating

Effect on Ti/Mg isothermal oxidation of refinement microstructure and tribological behaviour of pure aluminium alloy by plasma spray coating

Microstructure and corrosion resistance of novel rare-earth-zirconia doped Y2O3 plasma-sprayed coating

Y2O3 coatings are widely applied in semiconductor etching machines to protect the inner walls of aluminum alloys. This study reports the preparation of yttria-based coatings on aluminum alloy substrates using atmospheric laminar plasma spraying (ALPS) methods. In this study, four yttria-based coatings were designed and tested for their thermal performance, plasma etching resistance, and resistance to laser ablation. The rare-earth-zirconia (RE-ZrO2) doped Y2O3 coating exhibited the best thermal insulation performance, with a thermal conductivity of approximately 0.6 W m−1 k−1 at 600 °C. Plasma etching experiments demonstrated that more rare-earth fluorides were generated on the surface of the RE-ZrO2 doped Y2O3 coating, which weakened the plasma energy. Finally, the lowest etching rate was achieved. Laser ablation experiments demonstrated that the depth of the ablation pit on the surface of the RE-ZrO2 doped Y2O3 coating was shallow, indicating good laser ablation resistance. These results indicate that rare-earth-doped yttria-based coatings provide excellent corrosion protection against plasma etching and laser ablation.

Discrepancy evaluation in mechanics and corrosion resistance of reactive plasma sprayed TiN coatings fabricated under different heat treatment

Ceramic coatings have positive feedback to annealing treatment, but improper annealing treatment can also bring disastrous consequences. In this article, a thick TiN coating without a bonding layer was prepared by reactive plasma spraying technology and then subjected to heat treatment at three different temperatures in atmospheric and argon atmospheres. By exploring the hardness, modulus, and corrosion resistance of the coatings, combined with analysis of microstructure, phase composition, and interatomic bonding conditions, it was found that the TiN coating exhibited the lowest porosity after atmospheric heat treated at 500 °C. Meanwhile, it also showed the highest hardness, modulus, and optimal corrosion resistance. After heat treated at 650 °C in the atmosphere, the protective performance of the coating was decreased, but it was still far superior to the as-sprayed coating. The coating after heat treated in the argon atmosphere did not achieve ideal performance. The coating heat treated at 650 °C even exhibited inferior comprehensive performance to the as-sprayed coating. Therefore, it was summarized that the atmospheric environments and the temperature above the phase transition temperature were suitable for obtaining the optimal TiN coating.

The Etching Behaviour and Fluorine-Based-Plasma Resistance of YOF Coatings Deposited by Atmospheric Plasma Spraying

There is a high demand for plasma-resistant coatings that prevent the corrosion of the internal ceramic components of plasma etching equipment, thereby reducing particle contamination and process drift. Yttrium oxyfluoride (YOF) coatings were prepared using atmospheric plasma spraying (APS) with commercially available YOF/YF3 powder mixtures; namely YOF 3%, YOF 6%, and YOF 9%. The etching behaviour of YOF and yttrium oxide (Y2O3) coatings was investigated using an inductively coupled plasma consisting of NF3/He. X-ray photoelectron spectroscopy (XPS) showed that the YOF 6% coating had the thickest fluorinated layer. The scanning electron microscope (SEM) examination revealed that the YOF 6% coating showed exceptional resistance to erosion and generated a reduced quantity of contaminated particles in comparison to Y2O3. Consequently, it is more suitable as a protective material for the inner wall of reactors. The YOF coatings exhibit excellent stability and high resistance to erosion, indicating their appropriateness for use in the semiconductor industry.

Oxygen vacancy induced superhydrophobicity of air plasma spraying deposited Y2O3 coatings

Air plasma spraying (APS) is widely used for preparing superhydrophobic rare earth oxide (SH-REO) coatings due to its advantages of capable for large-scale and fast deployment with low cost. However, the origin of the superhydrophobicity remains unclear, which has impeded the design and development of robust APS-deposited SH-REO coatings. In this work, by studying APS-deposited superhydrophobic yttrium oxide (SH-Y2O3) coatings, we found a close correlation between oxygen vacancy and surface adsorbed species. Our results suggest that oxygen vacancy introduced during APS makes the Y2O3 surface liable to the adsorption of nonpolarized, hydrocarbon molecules, which contributes to a low-energy surface. Therefore, we showed the crucial role of oxygen vacancy in the acquirement of reliable SH-REO coatings.

A Comparison of the Tribological Properties of SiC Coatings Prepared via Atmospheric Plasma Spraying and Chemical Vapor Deposition for Carbon/Carbon Composites

The microstructure, mechanical performance, and tribological properties of SiC ceramic coatings prepared via atmospheric plasma spraying (APS) and chemical vapor deposition (CVD) method were compared to provide good anti-wear protection for carbon/carbon composites. The surface morphology of the APS-SiC coating was characterized as having a porous structure, whilst the CVD-SiC coating presented with many pyramidal-shaped crystals constituting the surface. The APS-SiC coating consists of a dominating SiC phase and a small fraction of the Si phase, while the XRD pattern of the CVD-SiC coating mainly consists of the SiC phase. The dense crystalline microstructure of the CVD-SiC coating made it possess a higher hardness and Young’s modulus at 31.0 GPa and 275 GPa, respectively. The higher H/E and H3/E2 parameters of the CVD-SiC coating implied that it exhibited better plastic resistance, which is also beneficial for anti-wear properties. The scratch test reflected the critical loads of the spallation of the APS-SiC coating and CVD-SiC coating, which were evaluated to be 25.9 N and 36.4 N, respectively. In the tribological test, the friction coefficient of the APS-SiC coating showed obvious fluctuations at high load due to damage to the SiC coating. The wear mechanism of the APS-SiC coating was dominated by abrasive wear and fatigue wear, while CVD-SiC was mainly dominated by abrasive wear. The wear rate of the CVD-SiC coating was far below that of the APS-SiC coating, suggesting the better wear-resistance of the CVD-SiC coating.

Degradation analysis of plasma sprayed metal-supported solid oxide fuel cell: The evolution of electrode processes under polarization

Metal-supported solid oxide fuel cells (MS-SOFCs) prepared by plasma spraying exhibit promising potential for scale-up applications, where the key lies in breaking through the challenges of limited lifetime and durability. Although electrochemical impedance spectroscopy (EIS) has been widely used to unfold the complex electrode processes in electrochemical reactions, there are still some concerns concerning the in-depth understanding and scientific evaluation of the degradation mechanism of cell long-term performance. In this study, the contribution of each resistance to the overall performance degradation is separately determined by coupled equivalent circuit model (ECM) based on the deconvolution of recorded EIS data at different DC biases. It is found that the deterioration of cathode surface oxygen exchange and O2− conduction causes more than 64 % of the total resistance increase, followed by the anode charge transfer reaction and gas-phase transport (24.91 %), and then the ohmic resistance (9.73 %). However, the correlation between the output voltage drop of MS-SOFC under load and the gas-phase diffusion resistance gradually increases, indicating a shift in the cell degradation mechanism. Combined with the post-test characterization of the aged cell, it can be inferred that the degradation is mainly attributed to the densification of the anodic microstructure and the cathodic elemental segregation. Additionally, attention should be paid to the effects of the thickening of the metal substrate oxide layer and thermal mismatch on the structural stability of MS-SOFC.

Fracture toughness and cavitation erosion behavior of Fe-based amorphous composite coatings with Ni-coated Al2O3 addition

Fe-based amorphous composite coatings were prepared on 304 stainless steel substrates using atmosphere plasma spraying (APS), aiming to investigate the effect of Ni-coated Al2O3 particles addition on fracture toughness and cavitation erosion behavior of Fe-based composite coatings. The microstructure, phase composition, elastic modulus, microhardness and fracture toughness of the coating were characterized using scanning electron microscopy with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), microhardness tester and nanoindentation. The cavitation erosion behavior of Fe-based coatings was investigated by ultrasonic vibration cavitation method. Fe-based amorphous composite coatings exhibit a characteristic lamellar microstructure and reveal the presence of amorphous phases along with α-(Fe, Cr), NiO, Ni and Al2O3 crystalline phases. When the content of Ni-coated Al2O3 in coating increases from 0 wt% to 3 wt%, there is slight deterioration in porosity from 3.64 % to 4.75 % and fracture toughness from 2.579 MPa·m1/2 to 2.392 MPa·m1/2, yet an increase in microhardness from 925.4 HV0.5 to 1090.3 HV0.5. The composite coating with 3 wt% Ni-coated Al2O3 demonstrates the peak cavitation resistance and its cumulative mass loss is significantly reduced by 36.4 % compared to the pure Fe-based coating. The cavitation erosion failure of Fe-based amorphous composite coatings is predominantly characterized by the brittle fracture mechanism. The fundamental process driving cavitation erosion damage involves the material peeling and coating delamination instigated by intense micro-jet impact and shock wave propagation. The proposed Fe-based amorphous composite coatings can be applied to improve the anti-cavitation performance of components in contact with high-speed fluids, such as ship propellers and centrifugal pump blades.

Ablation resistance of (Hf⅓Zr⅓Ta⅓)C solid solution ceramic coating for carbon/carbon composites at 2100 °C

Multicomponent solid solution ceramics have attracted extensive attention for their superior ablation resistance and high-temperature resistance, which are expected to extend the service life of carbon/carbon (C/C) composites under an ablation environment above 2000 °C. Herein, we synthesized (Hf⅓Zr⅓Ta⅓)C solid solution ceramic powders via carbothermal reduction. Then a dense (Hf⅓Zr⅓Ta⅓)C solid solution ceramic coating was deposited on SiC-coated C/C composites by supersonic atmospheric plasma spraying. The coated samples exhibited a low linear ablation rate of −0.61 μm/s after ablation for 120 s, mainly associated with the formation of a compact oxide scale consisting of (Hf, Zr)6Ta2O17 and (Hf, Zr)O2. The refractory (Hf, Zr)O2 skeleton structure possessed good thermal endurance, and the Ta-rich oxide melt filled the defects of the skeleton.

In-Situ and Ex-Situ Measurement of Stresses In Environmental Barrier Coatings

Abstract Ceramic Matrix Composites (CMCs) offer a step improvement in temperature capability over the current best high temperature super alloys for gas turbine applications. Silicon Carbide (SiC) based CMCs react with water vapor at temperature and therefore need an Environmental Barrier Coating (EBC) for protection against the water vapor attack. EBC is typically deposited on a CMC component through Air Plasma Spray (APS) process, which involves melting and fast quenching of molten ceramic powders (such as ytterbium disilicate and ytterbium monosilicate). The fast quenching and subsequent cool down to room temperature introduce residual stress in the EBC. In addition, EBC coated CMC components often go through a heat treatment process afterwards. For Ybsilicates, this both stabilizes/crystalizes the EBC and increases hermiticity by healing cracks and pores. This heat treatment at elevated temperature changes the coating residual stress state. It is important to be able to measure the coating stresses during deposition and heat treatment so that APS process improvement and EBC coating life assessment can be made. This paper describes novel methods to measure coating stresses continuously during APS and during heat treatment up to 1400°C, using an optical deformation and curvature-based approach.