Supersonic Atmospheric Plasma Spraying Research Articles

Thick and dense nitrogen-doped hafnium carbide ultra-high temperature thermal protection coating for outstanding ablation resistance up to 2600 ℃

Transition metal carbon-nitrides, typically represented by HfCN, have become the latest progress among the ultra-high temperature ceramics. In this study, single-phase solid solution HfCN coating was successfully synthesized from spray granulated HfC-HfN composite powder followed by employing the dual solid solution effects of radio frequency inductively coupled plasma spheroidization and supersonic atmospheric plasma spraying processes. The coating was nearly dense (only 2.3% in porosity) with a high thickness of ~ 270 μm. Compared with HfC coating, the HfCN coating exhibited higher hardness and elastic modulus. After plasma ablation at a high heat flux of 8.2MW/m2 for 200s, the HfCN coating exhibited a surface temperature of up to 2600 ℃ and can firmly protect the refractory tungsten substrate from oxidation failure. This outstanding performance illustrates that doping N element in HfC crystal can effectively improve the energy barrier for oxidation reaction and oxygen adsorption compared with typical HfC coating.

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.

Ablation behavior of Y2O3 modified HfC-based coatings for carbon/carbon composites above 2200°C

To improve the ablation resistance of C/C composites, Y2O3 with different contents modified HfC-MoSi2 multi-phase coating was prepared by supersonic atmospheric plasma spraying. The microstructural and phase compositional evolution of as-prepared coating was studied both before and after ablation. The effect of Y2O3 content on the ablation resistance and behavior of the coating was investigated in detail. The results showed that the incorporation of Y2O3 enhances the high-temperature stability of SiO2 oxide films and suppresses their volatilization at elevated temperatures. Furthermore, the formation of Y2Hf2O7 and Y2Si2O7 through the reaction between Y2O3, HfO2 and SiO2 promotes the development of a compact oxide scale, effectively inhibiting gas diffusion into the interior of the coating. Consequently, these improvements contribute to enhanced ablation resistance of the coating.

Investigation of ZrO2-toughened Yb2SiO5 environmental barrier coating on Nb alloy under water-vapor corrosion at 1500 °C

To protect niobium alloy against water-vapor corrosion at high temperatures, an innovative ZrO2-modified Yb2SiO5 environmental barrier coating was prepared via supersonic atmosphere plasma spraying. The service life of the modified coating (50 h) is 10 times higher than the pristine due to the higher fracture toughness (2.07 MPa∙m1/2) to inhibit cracking during frequent thermal cycles. With exposure prolonging, the in-situ formation of (Zr,Yb)O2 solid solution would weaken the fracture toughness of the coating by hindering the phase transformation of ZrO2 from cubic to monoclinic, while improving the corrosion resistance of the coating by enhancing atomic bonding strength.

Study on the corrosion performance of supersonic atmospheric plasma sprayed Cr3C2-NiCr coatings

PurposeDue to the harsh underground environment in coal mining, the surface of hydraulic support columns corrodes severely, resulting in significant economic losses. Therefore, a highly corrosion-resistant coatings is needed to extend the service life of the columns.Design/methodology/approachThis study aims to compare the corrosion resistance of ST-Cr3C2-NiCr (sealed treatment Cr3C2-NiCr) coatings with industrially applied chromium plating. The corrosion failure mechanism of the coatings was investigated.FindingsThe results demonstrated that the ST-Cr3C2-NiCr coatings exhibited excellent corrosion resistance. After sealing treatment, the corrosion potential of Cr3C2-NiCr coatings was −0.215 V, and the corrosion current density of Cr3C2-NiCr coatings was lower than that of the plated parts.Practical implicationsST-Cr3C2-NiCr coatings prepared by supersonic atmospheric plasma spraying could provide excellent corrosion resistance in the coal industry.Originality/valueThe low porosity and the presence of the NiCr phase were crucial factors contributing to the preferable corrosion resistance exhibited by the ST-Cr3C2-NiCr coatings. The corrosive process of the coatings involved layer-by-layer delamination of surface oxide film, sub-surface pitting, formation and degradation of sub-surface passive film, as well as severe block-like delamination.

The improvement of wear and corrosion resistance of nickel-graphite coating with modified graphite phase size

The corrosion resistance, friction and wear properties of an abradable seal coating are highly dependent on the size and distribution of lubrication phase. In this work, nickel-graphite (Ni-G) coatings were fabricated by a supersonic atmospheric plasma spraying system (SAPS) and a standard atmospheric plasma spraying system (APS), respectively. The effect of size and distribution of graphite phase on the performance of Ni-G coatings was investigated. The results suggested that the SAPS coating had an average single graphite phase area of 35.4 ± 5.1 μm2, which is approximately 35.4 % less than that of the APS coating, while the average graphite phase width and length in SAPS coating decreased by 22.2 % and 16.7 % compared to the APS coating. The fine distributed graphite phase improved the formation of structure with a small cathode and a large anode, which effectively increased the corrosion resistance of SAPS coating. The reciprocating sliding friction facilitated the creation of a uniform and uninterrupted lubricant layer, attributed to the finely dispersed graphite phase of SAPS coating. In comparison to the as-sprayed and subsequent corroded APS coatings, the friction coefficients of the SAPS coating exhibited a reduction of approximately 9.1 % and 13.3 %, respectively. The aforementioned findings showed that the small-sized graphite phase was conductive to the improvement of corrosion resistance, friction and wear properties of Ni-G abradable coatings.

Microstructure development of plasma sprayed dual-phase high entropy ceramic coating derived from spray dried and induction plasma spheroidized powder

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.

Corrosive Wear Mechanism of Supersonic Atmospheric Plasma Spray Coating of Hydraulic Supports in Industrial Environment

Corrosive Wear Mechanism of Supersonic Atmospheric Plasma Spray Coating of Hydraulic Supports in Industrial Environment

Ablation behavior of high-entropy boride (Hf-Zr-Ta-Ti)B2 coating fabricated via supersonic atmospheric plasma spraying for carbon/carbon composites

Carbon/carbon (C/C) composites have the potential to fulfill the demands of thermal protection systems, whereas they are limited by oxygen susceptibility. Herein, a high-entropy boride (HEB) (Hf-Zr-Ta-Ti)B2 coating was deposited on C/C composites via supersonic atmospheric plasma spraying for ablation-resistant applications. The coated C/C composites showed a linear recession rate of 1.14 μm/s after oxyacetylene torch testing for 60 s. The good ablation resistance is attributed to the multicomponent synergy effect. The Ti-dominated liquid phase sealed defects, resulting in a dense oxide scale, and the Ta-induced lamellar architecture potentially improved its thermal shock resistance. This study demonstrates that HEBs with compositional breadth are effective in protecting C/C composites from ablation at ultra-high temperatures.

Ablation resistance of ZrC coating modified by polymer-derived SiHfOC ceramic microspheres at ultrahigh temperature

Polymer-derived ceramics (PDCs) method opens up new possibilities for the preparation of novel multiphase ceramic nanocomposites owing to the molecular design of the precursors at the nanoscale level. In the current work, ZrC coatings incorporated with polymer-derived ceramic microspheres (CMS), SiHfOC_CMS, were deposited to enhance the ablation resistance by supersonic atmosphere plasma spraying. Upon 10.0 MW·m–2 plasma ablation at above 3000 °C, the linear ablation rate of ZrC-SiHfOC_CMS coating was reduced to 0.20 µm·s–1, 62% lower than that of the pristine ZrC coating. The improvement was ascribed to the presentence of viscous SiO2/HfO2 molten mixed phase, rather than HfSiO4, which can effectively seal pinholes and cracks. Moreover, the in-situ generated crystalline SiO2 had a lower oxygen diffusion rate than amorphous SiO2, meanwhile, m-HfO2 could improve the stability of SiO2 glassy film, thus further enhancing the ablation resistance.

Effects of modification of hBN by nickel plating on coating structure and properties of supersonic plasma spraying NiCr-Cr3C2-hBN@Ni coatings

Hexagonal boron nitride (hBN) with excellent self-lubrication performance is expected to relieve the friction resistance and wear of NiCr–Cr3C2 coatings. However, the poor wettability of hBN with most materials makes it difficult to fabricate NiCr–Cr3C2-hBN composite coating with good cohesion strength. In this study, hBN was firstly pretreated through magnetron-sputtering aided Ni plating to form hBN@Ni particles. Then, NiCr–Cr3C2-hBN@Ni powder was prepared by spray granulation. Next, corresponding coatings were prepared through supersonic atmosphere plasma spraying. It was found that in comparison with NiCr–Cr3C2-hBN coating, the NiCr–Cr3C2-hBN@Ni coating exhibited a decreased porosity (from 3.6% to 0.3%), elevated cohesion (from 52.78 N to 62.11 N), and the wear rate decreased by an order of magnitude. It was concluded that hBN@Ni can effectively improve the component interface inside powder, enhance the cohesion of molten in-flight particles, and make the internal structure of the coating denser.

Influencing factors and process optimization of Al[sbnd]25Si coating prepared by inner-hole supersonic atmospheric plasma spraying

For inner-hole parts, the main positions bearing load are their inner walls, which are prone to strain, wear, corrosion and other damages during use. Aluminum‑silicon (AlSi) coating (Al25Si) with excellent properties can be prepared through inner-hole supersonic atmospheric plasma spraying (SAPS) technology to provide reliable protection for inner-hole parts. In this paper, a study was conducted to find out how spray gas parameters, spray electrical parameters, and spray distances influence the temperature and velocity of flying particles during the process of preparing Al25Si coatings through inner-hole SAPS. Meanwhile, the coating preparation process was also optimized in this study. Through analysis and experimental verification, the optimal process parameters for preparing the coatings are as follows: The total gas flow is 115 L/min, the hydrogen (H2) content is 7.5 %, and the spray voltage, spray current, and spray distance remain at 86 V, 430 A, and 90 mm. Under these spray parameters, the particle temperature and flight velocity are 2698.7 °C and 473.9 m/s, respectively, while the porosity and microhardness of the coating are 0.79 % ± 0.56 % and 267.09 ± 14.85 HV 0.2, respectively.

Microstructure and water corrosion behavior of (Lu0.2Yb0.2Er0.2Tm0.2Sc0.2)2Si2O7 high-entropy rare-earth disilicate coating for SiC coated C/C composites

In order to make carbon/carbon composites suitable for application in gas turbine engine, it is necessary to develop environmental barrier coatings (EBCs) to protect them from reacting with water vapor. In our previous work, a novel high-entropy rare-earth disilicate (Lu0.2Yb0.2Er0.2Tm0.2Sc0.2)2Si2O7 ((5RE0.2)2Si2O7) has been developed and verified as a promising candidate for EBCs. In this work, the (5RE0.2)2Si2O7 coating was synthesized on the surface of SiC coated C/C composites by supersonic atmospheric plasma spraying method. The protective performance and mechanism of this coating under high temperature water vapor environment was explored in detail. Results showed that the weight change of the sample coated with (5RE0.2)2Si2O7 was only 0.2% after corrosion for 100 h at 1500 ºC, which proved that (5RE0.2)2Si2O7 coating could significantly improve the resistance of C/C composites against water vapor corrosion. This work may provide theoretical basis for the design and application of high-entropy rare-earth silicates as EBCs.

Plasma Coatings for Protection Against Hydroabrasive and Cavitation Wear

The results of research work on the application of coatings designed to protect the working surfaces of machine parts and mechanisms operating under conditions of hydroabrasive and cavitation wear are presented. Coatings were produced by supersonic atmospheric plasma spraying of powder materials using air as a plasma gas. The experimental list of materials was chosen taking into account the experience of the authors in protecting the details of the propulsion and steering complex of river vessels using coatings applied by subsonic thermal plasma flows.

In-situ phase evolution of multi-component boride to high-entropy ceramic upon ultra-high temperature ablation

Multi-component boride (Hf0.5Zr0.5)B2-SmB6-ErB4-YB6 (HZRB) utilized as a coating on SiC-coated carbon/carbon (C/C) composite was prepared by supersonic atmosphere plasma spraying. In-situ phase evolution of HZRB into (Hf0.2Zr0.2Sm0.2Er0.2Y0.2)O2-δ high-entropy oxide (HEO) was investigated after oxyacetylene ablation for 120 s. The first-principles calculations were applied to analyze the in-situ formation mechanism of HEO. The mixing Gibbs free energy change (∆Gmix) of HEO was calculated to be negative at 2573 K, indicating that the HEO can be generated upon the ablation temperature. Due to the lower Gibbs free energy change of reaction (∆RGm), (Hf0.5Zr0.5)B2 will be oxidized to generate HfO2 firstly, and other elements dissolved into the HfO2 lattice to form HEO. The solution energies of Zr, Sm, Er and Y atoms are − 0.01, 6.28, 8.55 and 4.46 eV/atom, and corresponding solution reactions possess negative ∆RGm, indicating the possible solution sequence of these elements is Zr > Y > Sm > Er.

Sealing role of Ti-rich phase in HfC-ZrC-TiC coating for C/C composites during ablation above 2100 °C

Traditional HfC, ZrC, and HfC-ZrC coatings cannot resist long-term ablation above 2100 °C because their oxides (HfO2 and ZrO2) express a loose structure and poor anti-oxygen infiltration ability after ablation. While Ti-rich oxides with a lower melting point can seal this loose structure during ablation. In this work, a HfC-ZrC-TiC multi-phases coating was proposed to solve the ablation failure problem of these coatings. It was prepared by supersonic atmospheric plasma spraying and tested by ablation with a heat flux of 2.38 MW/m2. With time ranging from 30 s to 120 s, the mass and linear ablation rates decreased from 0.85 mg/s to 0.18 mg/s and from 2.58 µm/s to 0.71 µm/s, respectively. All positive values indicated an increase in all coating thicknesses, so this coating can effectively protect C/C composites for more than 120 s. The surface of the coating was mainly composed of a loose oxide m-(Hf, Zr, Ti)O2 skeleton within 120 s. As oxide skeletons had been gradually destroyed by mechanical denudation, the liquid phase of (Hf, Zr)TiO4 was formed under oxide skeletons to fill pores. Then the surface of the oxide layer was dense after 120 s. The self-healing ability of the HfC-ZrC-TiC coating improved the ablation resistance of C/C composites above 2100 °C.

MoSi2 modified HfC coating for the ablation protection of SiC-coated C/C composites: Ablation resistance and behavior

To improve the ablation resistance of HfC coating, HfC-MoSi2 coatings with different MoSi2 content were prepared on SiC-coated carbon/carbon (C/C) composites by supersonic atmospheric plasma spraying (SAPS). The effects of MoSi2 content on the microstructure, phase composition and ablation behavior of HfC-MoSi2 coating were investigated. The ablation resistance of as-prepared coatings was tested under the oxyacetylene flame with a heat flux of 2.4 MW/m2. The results showed that the HfC-(25 vol%) MoSi2 coating exhibited better ablation resistance, and its mass and linear ablation rate are 0.23 mg/s and 0.48 µm/s, respectively. Such good performance was ascribed to the formation of Hf-Si-O compound phases, which effectively filled the diffusion channel of oxygen and improved the compactness of the coating.

Effect of heat treatment on corrosion resistance of supersonic atmospheric plasma-sprayed Cr3C2–NiCr coating

Supersonic atmospheric plasma spraying (SAPS) is a newly developed technique in preparing high-performance Cr3C2–NiCr coatings with a high deposition efficiency. In this work, the effect of post-heat treatment on carbide precipitation and corrosion property of the SAPS Cr3C2–NiCr coatings was investigated. The results suggested that heat treatment induced the precipitation of secondary carbide grains, and the size of these carbides increased with the increasing heat treatment temperature. In addition, the self-corrosion current density of the coatings thermally treated at 500∘C was seven times smaller than that of the coating without heat treatment. The corrosion morphology showed that significant corrosion cracks were present on the as-sprayed coating. In contrast, the heat-treated coatings demonstrated small corrosion holes due to the formation of small corrosion galvanic cells between the precipitation of carbides and the substrate.

Comparative study on the effects of α/γ phase ratio on the micro-structures and properties in Al2O3 coatings under silicon ion irradiation

In this work, the Al2O3 tritium permeate barriers (TPBs) with controllable α/γ phase ratios were prepared by supersonic atmospheric plasma spraying. A comparative study was carried out to explore micro-structure, irradiation tolerance, corrosion property and mechanical properties in the Al2O3 coatings with different α phase ratios (77.6 ± 3.9% and 23.4 ± 1.2%, respectively) irradiated by Si+ with fluence from 5 × 1015 to 5 × 1016 cm−2 at room temperature. Results indicated a quite stable in crystalline structure and diverse irradiation-defect in two kinds of Al2O3 coatings after irradiation. The lower corrosion current densities were measured in the higher α phase Al2O3 coatings before and after Si + irradiation. Also, the vacancy-clusters and dislocations aggregated from point defects are main reasons to explain the increase in mechanical properties at low fluence. The smaller dislocation loops and its less distribution are responsible for the more stable evolution-tendency in hardness and fracture toughness for the higher α phase Al2O3 coating irradiated at fluence of 5 × 1016 cm−2. And this investigation results provide a basic reference for TPBs design by supersonic atmospheric plasma spraying (SAPS) technology for future fusion reactor.

The Structure and Characteristics of Wear-Resistant Coatings, Obtained by Supersonic Plasma Spraying

The characteristics of coatings designed to protect against cavitation and waterjet wear, obtained by supersonic atmospheric plasma spraying using air as a plasma-forming gas, are studied. The following powder materials were selected for coating: WC/10Co4Cr; Ni-Cr-B-Si-C; Ni-Al; Ni-Ti; bronze. Metallographic studies of the structures of specimens with applied coatings and measurements of their microhardness were carried out. Due to the fact that the tests of materials for hydroabrasive wear are not standardized, studies were carried out on the resistance of coatings to dry abrasive wear according to the ASTM G65-04 standard and to dry reciprocating friction according to the ASTM G133 standard. The conducted studies of the structures of the sprayed coatings suggest that the use of supersonic deposition modes guarantees the production of high-density coatings with a porosity of less than 1 %.