Supersonic Atmospheric Plasma Spraying Research Articles

MoSi2-HfC/TaC-HfC multi-phase coatings synthesized by supersonic atmospheric plasma spraying for C/C composites against ablation

To improve the ablation resistance of C/C composites, MoSi2-HfC/TaC-HfC (MH/TH) bilayer coatings were synthesized on SiC coated C/C composites. Results showed that the mass and linear ablation rate of MH/TH coatings were 0.236 mg/s and 1.026 µm/s, respectively. The excellent performance of MH/TH coatings was attributed to the combination of TH and MH layers. The external TH layer could create Ta2O5 and Hf6Ta2O17 glassy phase to protect the internal layer and prevent the formation of destructive MoO3. Meanwhile, the decomposition of the internal MH layer to produce SiO2 diffusion outward could retard the destruction of the external coating.

Ablation resistant ZrC coating modified by polymer-derived SiC/TiC nanocomposites for ultra-high temperature application

To improve the ablation resistance of ZrC coating on SiC-coated carbon/carbon composites above 2000 °C, SiC/TiC nanocomposites (SiC/TiC-NCs) powders derived from single-source precursor were incorporated into ZrC coating, denoted as ZrC-SiC/TiC-NCs, via supersonic atmospheric plasma spraying (SAPS). After SAPS, the incorporated SiC/TiC-NCs evolved into TiC/(SiC and ZrxTiyC) embedded in amorphous SiC. The ablation resistance of the ZrC-SiC/TiC-NCs coating was evaluated by oxyacetylene flames with a heat flux of 4.18 MW/m2. For comparison, the ZrC-SiC-NCs coating without Ti modification was seriously damaged due to rapid gas denudation. The good ablation resistance of ZrC-SiC/TiC-NCs coating is mainly attributed to the distinctive “capsule-like” multi-crystalline microstructure of SiC/TiC-NCs. During ablation, TiO2 and ZrxTiyO2, due to the oxidation of TiC and ZrxTiyC, contributed to the formation of Zr-Ti-Si-O glass with high viscosity and low evaporation pressure, improving the ablation resistance.

Study on the biological behaviors of Ca[sbnd]P coatings with different morphology on carbon/carbon composites

In this work, we designed and fabricated a CaP composite bio-coating with different surface morphologies on a carbon/carbon (C/C) matrix by means of hybrid supersonic atmospheric plasma spraying (SAPS) and microwave-hydrothermal (MH) technologies. We found that all studied coating materials can support mesenchymal stem cells (MSCs) proliferation with prolonged culture time (3 days and 7 days) in vitro. Furthermore, according to the (Confocal Laser Scanning Microscopy) CLSM results, the MSCs also showed good attachment and different spreading morphologies on SAPS/MH coatings. As such, C/C matrix, the MH treated coatings with needle-like and rod-like microstructures were chosen for further in vivo investigation. Considering the good bonding between host tissue and the studied materials, the in vivo morphology studies confirmed a good histocompatibility for all coating samples, as well as a decreasing expression for inflammatory factors in a physiological environment. The histological results around the implants indicated different cell aggregation and vascularization ability in the local micro-environment. In particular, based on the reduction of the C/C initial surface flaws (e.g. hydrophobicity, biological inertia and easily producing carbon fragments or particles), the MH treated coating with rod-like surface morphology with a specific surface area (~2.33 m2/g) and roughness (~13.80 μm), showed excellent performance as a promising implant in live tissue.

Microstructural optimization and anti-wear performance of supersonic atmospheric plasma sprayed nickel based self-lubricating coatings under heavy load

The aim of this work is to explore high-property nickel based self-lubricating coatings to meet the challenge of the increasing demand of heavy load wear condition. Thus, a series of Ni-MoS2/graphite coatings were designed and prepared by supersonic atmospheric plasma spraying. The microstructural evolution of lubricating phases was systematically studied by plasma focused ion beam (FIB) and field-emission transmission electron microscopy (FE-TEM). The results suggested that the lubricating phases, such as graphite and MoS2, can transform into some independent lamellar structures due to their low binding energy. MoS2 phase was easy to decompose into nanoscale Mo with preferred (110) crystal plane at high temperatures, leading to the decrease of self-lubrication property of coatings. Due to the rapid formation of the graphite-dominated debris transfer layer, the coating with approximately 19 vol% graphite showed the longest friction time and the lowest wear rate. The graphite with a large size range (1–60 μm) not only effectively compensated the loss of MoS2 caused by the thermal decomposition, but also improved the density and fracture toughness of coatings. In addition, the content of monoclinic β-MoO3 was significantly decreased with the addition of graphite, which further improved the tribological properties of the coatings. This work provided an in-depth understanding for the development of composite coatings with high anti-wear performance under heavy load.

Ablation behavior of ZrC and ZrO2 coatings on SiC coated C/C composites under oxyacetylene torch with different heat fluxes

In this work, ZrC and ZrO2 coatings were prepared on SiC-coated carbon/carbon (C/C) composites by supersonic atmospheric plasma spraying. Their ablation behavior was investigated and compared under different heat fluxes to design multilayer anti-ablation structural coating. Results shown that ZrO2 coating exhibited denser oxide layer and lower mass consumption after ablation. According to their microstructure and thermal analysis, possible reasons can be ascribed to higher surface temperature and lower melting point of ZrO2 coating, which made the scale easier to be sintered during ablation. Moreover, the ablated ZrC coating presented particle accumulation structure at the initial ablation stage, hence causing the consumption from mechanical denudation to occur in these particles preferentially rather than sintering.

Self-healing performance of niobium suboxide-based solid solution for UHTC coating during oxyacetylene test

In this work, NbC coatings modified with different contents (0, 25 and 50 mol%) of HfC were deposited on SiC-coated C/C composites via supersonic atmospheric plasma spraying to study the effect of HfC on the ablation-resistance of the NbC coatings under an oxyacetylene torch. The phase composition and chemical states of Nb2O5–66.67 mol% HfO2 plates heated up to 2100 °C in an Ar atmosphere were investigated. The results confirmed that the effective ablation time of the NbC-coating mixed with 50 mol% HfC was approximately 120 s, which is more than twice that of the pure NbC coating. During air quenching, NbO and NbO2 ultimately transformed into Nb2O5, producing compressive stress that stabilized the t-HfO2 crystals. Furthermore, the formation of hafnium oxide significantly improved the thermal stability and viscosity of the NbO film, and the niobium suboxide-based solid solution, possessing an attractive self-healing performance, increased the compactness of the HfO2-based solid solution layer are responsible for the superior ablation performance of the NbC-HfC coating.

Influence of in-flight particle characteristics and substrate temperature on the formation mechanisms of hypereutectic Al-Si-Cu coatings prepared by supersonic atmospheric plasma spraying

Hypereutectic Al-Si-Cu coatings were prepared by supersonic atmospheric plasma spraying to enhance the surface performance of lightweight alloys. To find out optimum process conditions and achieve desirable coatings, this work focuses on the influence of three important parameters (in-flight particle temperature, impact velocity, and substrate temperature) on the collected splats morphology, coatings microstructure and microhardness. Results show that appropriate combinations of temperature and velocity of in-flight particles cannot only completely melt hypereutectic Al-Si-Cu particles, especially the primary Si phase, but also provide the particles with sufficient kinetic energy. Thus, the optimized coating consists of 98.6 % of fully-melted region with nanosized coupled eutectic and 0.9 % of porosity. Increasing the substrate deposition temperature promotes the transition from inhomogeneous banded microstructure to homogeneous equiaxed microstructure with a lower porosity level. The observations are further interpreted by a newly developed phase-change heat transfer model on quantitatively revealing the solidification and remelting behaviors of several splats deposited on substrate. Besides, phase evolutions including the formation of supersaturated α-Al matrix solid solution, growth of Si and Al2Cu phases at different process conditions are elaborated. An ideal microstructure (low fractions of unmelted/partially-melted regions and defects) together with solid solution, grain refinement, and second phase strengthening effects contributes to the enhanced microhardness of coating. This integrated study not only provides a framework for optimizing Al-Si based coatings via thermal spraying but also gives valuable insights into the formation mechanisms of this class of coating materials.

Ablation resistance of HfC-TaC/HfC-SiC alternate coating for SiC-coated carbon/carbon composites under cyclic ablation

HfC-TaC/HfC-SiC alternate coatings with different sublayer thicknesses were fabricated on SiC-coated carbon/carbon composites by supersonic atmosphere plasma spraying. Their ablation resistance was studied under oxyacetylene torch and compared with monolayered HfC-TaC coating. The alternate coating with 6 spray cycles of HfC-TaC and 3 spray cycles of HfC-SiC sublayers exhibited the best ablation performance as confirmed by the integral coating morphology and the lowest ablation rates. A dense oxide layer acting as an oxygen insulator and the release of thermal stress induced by the formation of dendritic cracks are thought to be responsible for its great ablation resistance. For the alternate coating with 4 spray cycles of HfC-TaC and 2 spray cycles of HfC-SiC sublayers, exfoliation occurred at the interface of two adjacent sublayers, leading to violent evaporation of exposed HfC-SiC sublayer.

Multi-layered structural designs of MoSi2/mullite anti-oxidation coating for SiC-coated C/C composites

The gradient and laminated multi-layered MoSi2-mullite coatings were prepared with similar thickness by supersonic atmosphere plasma spraying (SAPS) on SiC coated C/C composites to analyze the effects of the two multi-layered structure on the oxidation resistance of SAPS MoSi2 coating under high temperature environment. Unexpectedly, the gradient multi-layered design showed almost no positive effect on the protective performance improvement in comparison to the monolayer MoSi2 coating. The laminated multi-layered design remarkably improved the oxidation resistance at 1500 °C, up to 226 h, as well as the thermal shock resistance to 30 thermal cycles with only half the mass loss of the monolayer one. Such obvious improvement in the laminated MoSi2/mullite multi-layered coating was attributed to the effect of macroscopic interfaces on the auxiliary self-healing and the change of thermal stress field, which were conducive to hindering further crack prolongation.

Preparation and properties of supersonic atmospheric plasma sprayed TiB2−SiC coating

Abstract With the TiB2−SiC powders after spray granulation and vacuum calcination as raw materials, the TiB2−SiC coating was prepared by supersonic atmospheric plasma spraying (SAPS). The effects of spraying power and spraying distance on the properties of the TiB2−SiC coating were investigated and the fabrication processing of SAPS was optimized. The results show that the sprayed powders after calcination have a uniform particle size distribution, good sphericity and enhanced fluidity. The coating prepared by the calcined powders has a dense structure and high deposition efficiency. When the calcined TiB2−SiC powders are used and the spraying power is 95 kW and the spraying distance is 150 mm during supersonic plasma spraying, the obtained TiB2−SiC coating behaves the best comprehensive performance with the porosity, microhardness, bonding strength and resistivity equal to 5.6%, 3.57 GPa, 18.3 MPa and 10.8 mΩ·cm, respectively.

High-temperature tribological behavior of thermally-treated supersonic plasma sprayed Cr3C2-NiCr coatings

Supersonic atmosphere plasma spraying (SAPS) can deposit Cr3C2-NiCr coatings in a very high efficiency to provide excellent anti-wear performance at high temperature. In the present work, the effect of post heat treatment on the microstructural evolution and the high-temperature wear performance (at 400 °C) of the Cr3C2-NiCr coatings was investigated. It is found that SAPS process facilitated the carbide dissolution/diffusion during particle flight while nano-sized carbides began to sufficiently precipitate from the supersaturated NiCr binder during post heat treatment. However, carbide decarburization could not be completely constrained and the volume fraction of carbide in the coating even thermally-treated at 750 °C was lower than that of original powders. The coating thermally-treated at 500 °C presented the highest hardness due to the precipitation strengthening of secondary carbides, which also induced the best wear-resistant property. Overall, the wear behavior of the coatings was correlated with the abrasive wear

Effect of Mild Oxidation on Ablation Properties of ZrSiO4 Coating Prepared by Supersonic Atmospheric Plasma Spraying on Carbon/Carbon Composites

To eliminate the thermal expansion mismatch and improve the bonding strength between ZrSiO4 coating prepared by supersonic atmospheric plasma spraying and C/C composites, a layer with porous structure was produced on the substrate by a preliminary air oxidation treatment. The morphology and microstructure of the ZrSiO4 coating were characterized by SEM and XRD. The results showed the coating prepared under the condition of mild oxidation treatment exhibited good bonding strength and outstanding anti-ablation ability. After ablation for 120 s, the linear and mass ablation rates of the samples with mild oxidation were − 1.5 × 10−4 mm/s and 0.88 × 10−3 g/s, respectively, which were lower than those without oxidation treatment. The bonding strength of the samples with mild oxidation reached 7.9 MPa, which was 97.4% higher than those without mild oxidation. The excellent ablation resistance is attributed to the fact that oxidation treatment could make the surface rougher and enhance the bonding strength to decrease the thermal stress between the coating and substrate.

Anti-ablation performance of La2O3-modified ZrB2 coating on SiC-coated carbon/carbon composites

La2O3-modified ZrB2 coating was prepared on SiC-coated C/C composites by supersonic atmospheric plasma spraying (SAPS) with the aim of improving the anti-ablation performance of C/C composites. The effect of La2O3 contents on the anti-ablation performance were investigated. The results indicated that the 10 vol % La2O3–ZrB2 coating shows excellent anti-ablation performance. After ablation for 120 s under low heat flux oxyacetylene flame (2400 kW/m2), the linear ablation rate and mass ablation are only −0.0167 μm/s and −0.558 mg/s, respectively. After ablation for 30 s under high heat flux of oxyacetylene flame (4200 kW/m2), the coating still remains intact. The addition of 10 vol % La2O3 is capable of enhancing the anti-ablation performance of the ZrB2 coating. The La2O3 and La2Zr2O7 phases will be soften and melting during ablation, which can form a barrier to cover the surface and effectively prevent the erosion of oxyacetylene gas. Meanwhile, the generated ZrO2 particles play the role of pinning the molten layer, thus weakening the coating exfoliation by airflow erosion.

Effect of sprayed techniques on the surface microstructure and in vitro behavior of nano-HAp coatings.

Supersonic atmospheric plasma spray (SAPS) technique is a classical method which is employed to coat the carbon/carbon (C/C) composites by nano-hydroxyapatite (HAp) powders to decrease the biologically inert, hydrophobic drawbacks of substrate surfaces. In recent years, profiting from the promoting of energy conservation and environmental protection, more emphasis was placed on industrial manufacturing to simplify the experimental steps. This paper aims to study the preparation of nano-HAp coatings by suspension plasma spray (SPS) instead of the original SAPS technique. A denser, more uniform and less defective coating is successfully fabricated on C/C substrate using SPS technique. More important, fewer surface flaws in SPS coating could be observed by scanning electron microscopy (SEM) which shows that the large drawbacks of the coating have disappeared during spraying process. Meanwhile, except for HAp, phase compositions of the SPS coating appear with slight calcium oxide (CaO, 0.8%) and tricalcium phosphate (TCP, 30.7%), and then all CaO as well as TCP phases transform into dicalcium phosphate anhydrous (DCPA, 60.6%) after microwave-hydrothermal (MH) treatment. Thermal analysis (TG/DSC) reveals that SPS coating (97.51%) has a higher thermal stability than that of the SAPS coating (82.37%). Also, in comparison, the SPS coating after MH treatment (SPS-MH coating) exhibits better thermal properties (92.76%). In addition, compared to the SAPS and SPS coatings, due to the more flaw reduction and phase transformation, SPS-MH coating shows a better biological properties according to the surface microstructure in simulation body fluid (SBF) solution and cell spreading area on coating. The highest corrosion resistance with the current density of 3.9798×10-7 A/cm2 and a potential of 0.0419V is achieved for SPS-MH coating.

Ablation behavior of sharp leading edge parts made of rare earth La-compound modified ZrB2 coated C/C composites

LaB6-ZrB2 and La2O3-ZrB2 coating were prepared on the sharp leading edge shaped C/C composites by supersonic atmosphere plasma spraying and their oxyacetylene ablation behavior were investigated. Results indicated that the oxide scale generated after ablation of LaB6-ZrB2 coating presented porous due to the excess B content, which decreased the compactness. For La2O3-ZrB2 coating, La2O3 dissolved into ZrO2by diffusion, forming a dense oxide scale containing La0.1Zr0.9O1.95, which offered the best ablation protection. Moreover, the analysis of La2O3-ZrB2 coating in combination with computational fluid dynamics simulation revealed the ablation behavior of different areas.

Effect of tantalum carbide on the ablation behaviors of hafnium carbide coating for C/C composites under single and cyclic oxyacetylene torch environments

A HfC-TaC/SiC multilayer coating was synthesized on carbon/carbon (C/C) composites by supersonic atmospheric plasma spray (SAPS) and pack cementation (PC) methods. Ablation performance of the coating was characterized under single and cyclic oxyacetylene torch with a heat flux of 4.18 MW/m2, and the phase composition and morphology of the oxide layer were surveyed systematically. During single ablation, a continuous Hf-Ta-O compound scale was formed on the surface, which is responsible for the better ablation performance of HfC-TaC coating compared with monophasic HfC coating. As for cyclic ablation, ablation crater appears on both HfC and HfC-TaC coating surfaces due to the multiple thermal shocks, but the size of the latter is reduced significantly.

Formation mechanism of gas phase in supersonic atmospheric plasma sprayed NiCr-Cr3C2 cermet coatings

A typical plasma sprayed NiCr-Cr3C2 cermet coating usually consists of carbides, metal binder and gas phase. Among these phases, the gas phase has a great influence on the mechanical properties of as-sprayed coating. However, an in-depth understanding of the formation mechanism of gas phase is still lacking. Therefore, in the present work, the NiCr-Cr3C2 cermet coatings were deposited by supersonic atmospheric plasma spraying method and the formation of gas phase was discussed by the collection of flattened particles. Results showed that the flattened particles showed characteristics of multi-layer solidification. The bubbles inside or on the surface of flattened particles were mainly formed by the gas porosity and gas shrinkage, and then some pores were formed under non-equilibrium solidification. The number and size of pores gradually decreased with the increase of gas solubility and cooling rate, which resulted in the formation of NiCr-Cr3C2 coating with lower porosity and higher microhardness. A theoretical model based on experiments was also proposed to elaborate the formation mechanism of gas phase inside cermet coatings.

Evolution behavior of rare-earth yttria modified silicide oxidation-resistant coating at 1700 oC

Yttria-modified silicide (MoSi2-Y2O3) oxidation-resistant coatings with multiple Y2O3 contents were prepared using supersonic atmospheric plasma spraying, and the oxidation resistance was investigated at 1700 °C with static atmosphere. Experimental results indicated that the sprayed MoSi2-Y2O3 coating possessed good compactness, which adhered well to the SiC transition layer. Meanwhile, the Y2O3 addition greatly enhanced the bonding strength of the coating, and extended its service life at 1700 °C. Wherein the MoSi2-20 wt.%Y2O3 coating exhibited the highest adhesive strength and best oxidation resistance with the lowest mass loss among all the coatings. In practice, the Y2O3 changed the microstructures of formed oxide glass scale during oxidation, and then modified the oxidation resistance of the coating. The action mechanism of Y2O3 on the oxidation behavior of MoSi2-Y2O3 coating was analyzed.

Influence of NbC-doping on the microstructure and thermo-mechanical properties of tungsten coating fabricated by supersonic atmospheric plasma spraying

In this study, NbC-free and NbC-doped tungsten powders were thermally sprayed via a supersonic atmospheric plasma spraying (SAPS) onto reduced activation steel substrates to form coatings. Scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectrometry analyses, as well as thermal diffusivity, thermal conductivity, hardness and Young's modulus measurements, were used to characterize the influences of NbC-doping on the microstructure and thermo-mechanical properties of tungsten coating. The results demonstrated that the coatings all had a typical thermal spraying microstructure characterized by the lamellar structure, the splat boundary, and the pores or holes. NbC-doping decreased the porosity and increased the lamellar thickness of tungsten coating. WO3 and (Nb, W)2O5 produced by inevitable metallurgical physical chemistry reactions in SAPS process existed in the NbC-free and NbC-doped coatings, respectively. Those oxides generated by metallurgical physical chemistry reactions were changed from ellipsoid morphology with sharp poles and distributed on the grain boundaries in the NbC-free coating into quasi-spherical morphology and distributed mainly in grains in the NbC-doped coating. Thermo-mechanical properties such as thermal diffusivity, thermal conductivity, hardness, Young's modulus, and the ability to resist cracking of tungsten coating were improved after the doping of NbC.

Investigation on the ablation performance and mechanism of HfC coating modified with TaC

HfC coatings modified with different TaC contents were designed and successfully deposited on SiC-coated carbon/carbon (C/C) composites by supersonic atmosphere plasma spraying. The phase composition, morphology, and ablation resistance were surveyed, and the structural evolution of the oxide layer was studied as well. Results indicated that HfC coating with 10 vol.% TaC exhibited superior ablation resistance compared with the other compositions, as proved by the ablation rates and surface morphologies. The optical HfC/TaC volume fraction offers an oxide layer with adequate unmelted particles (HfO2 and Hf6Ta2O17) withstanding airflow scouring and moderate liquid phase (Ta2O5) impeding oxygen infiltration.