Plasma Spraying Technology Research Articles

Enhanced Anti-Corrosion and Biological Performance of Plasma-Sprayed Nb/ZrO2/HA Coatings on ZK60 Mg Alloy

Niobium (Nb) and zirconium dioxide (ZrO2) were doped into hydroxyapatite (HA) to fabricate HA-based composite coatings prepared on a ZK60 magnesium alloy by plasma spraying technology to improve anti-corrosion and biocompatibility for clinical applications. The results revealed that the Nb-enriched coating exhibits fewer cracks and pores with a flat surface due to the decreased temperature gradient during spraying, and small needle-like structures can fill the cracks and pores in the ZrO2-contained coating, resulting in a more uniform and dense surface. Compared to coatings with only niobium or zirconium dioxide, the ZrO2/Nb/HA composite coating significantly enhanced the mechanical properties and corrosion resistance of the magnesium alloys. Among all the specimens, the ZrO2/HA coating and ZrO2/Nb/HA coating revealed high surface hardness values (327.73 HV and 293.80 HV, respectively). However, the higher hardness value made the ZrO2/HA coating fragile and more likely to crack, while the ZrO2/Nb/HA coating avoided this shortcoming and exhibited a more comprehensive performance. During immersion tests, the ZrO2/Nb/HA coating exhibited a gradual pH increase and minimal mass loss, and the cytocompatibility test demonstrated promising cellular activity.

A comparison of cold spray, atmospheric plasma spray and high velocity oxy fuel processes for WC-Co coatings deposition through LCA and LCCA

In this study, an environmental and economic assessment of WC-Co coatings deposited by Cold Gas Spray (CGS), Atmospheric Plasma Spray (APS) and High Velocity Oxy Fuel (HVOF) spray technologies is carried out. Using SimaPro LCA software, several environmental impact categories are analyzed to compare their environmental performance. The economic analysis includes capital and operating expenditures. The results have highlighted that all three processes exhibit low environmental impact in terms of CO2 emissions but the performance of the CGS process is heavily influenced by the low deformability of WC-Co, while the APS process is affected by high electricity consumption. In terms of economic analysis, the HVOF process exhibits the best performance, while the CGS process requires most time to deposit the coating, and consequently, it is the process where the workforce component is most significant. These results depend on the fact that CGS might not be the most suitable deposition technique for fabricating WC-Co coatings.

Microstructure and properties of plasma sprayed NbC-Al2O3 composite coatings

Niobium carbide has received widespread attention due to its high melting point, high strength, high chemical stability and high wear resistance, but the current preparation of niobium carbide coatings using plasma spraying technology suffers from low deposition efficiency, poor fusibility of the composite powders, high porosity, and high defects in the coating microstructure. Therefore, the microstructure and properties of NbC-Al2O3 composite coatings prepared by plasma spraying NbC-Al2O3-SiC composite powder and reactive plasma spraying Nb2O5-SiC-Al composite powder were comparatively investigated in this paper. The reaction mechanism of Nb2O5-SiC-Al composite powder during plasma spraying as well as the mechanism of the formation of coatings were analyzed in detail. The results showed that compared with the ex-situ NbC-Al2O3-SiC coating fabricated by plasma spraying, the in-situ Nb2O5-SiC-Al composite coating prepared by reactive plasma spraying had an obvious layer structure, low porosity (5.8%), high hardness (1141 HV0.1), high toughness (22.94 J/m2), and good scratch resistance properties.

Microstructure and properties of Al/FeCoNiCrMo coatings prepared by different plasma spraying currents on carbon fiber reinforced plastic surfaces

Al/FeCoNiCrMo high-entropy alloy (HEA) coatings were prepared on the surface of carbon fiber reinforced plastic using plasma spraying technology. The microstructure of the HEA coatings was characterized under different spraying currents, and the hardness, interfacial bonding, corrosion resistance and friction and wear properties of the coatings were tested. The results showed that with the increase of the current, the unfused particles in the coatings decreased, and the coating porosity and thickness also decreased gradually; the hardness, corrosion resistance and friction and wear resistance properties increased with the increase of the current, in which the maximum hardness was 740.3 HV0.1, and the minimum self-corrosion current was 1.21 × 10−5 A·cm−2, and the minimum volumetric wear rate was 7.66 × 10−5 mm3·N−1·m−1.

Thermal cycling property of the novel Hf6Ta2O17/YSZ TBCs prepared by atmospheric plasma spraying technology

Hf6Ta2O17, with low thermal conductivity, high thermal expansion coefficient, and excellent fracture toughness, was a promising candidate ceramic top coat material of thermal barrier coating (TBC). A novel Hf6Ta2O17/YSZ double ceramic top coat prepared by atmospheric plasma spraying (APS) was applied to study the role of the microstructure and mechanical property on the thermal cycling property at 1200 °C. Results show that the rapid decomposition of Hf6Ta2O17 occurred during the spraying process. As the increased spraying power, more HfO2 phases were observed in the Hf6Ta2O17/YSZ TBCs. Besides, the porosity of the Hf6Ta2O17 ceramic top coat decreased with the increased spraying power, resulting in the elastic modulus of the Hf6Ta2O17 ceramic top coat enhancement. The highest cycles at 1200 °C were obtained for the Hf6Ta2O17/YSZ TBCs with the lowest elastic modulus and least HfO2 phases, and were twice as long as the cycles of the single YSZ TBCs. The chemical reaction between HfO2 and Hf6Ta2O17 might have contributed to the cracking of the Hf6Ta2O17/YSZ TBCs. This work provides a new option for the preparation and development of the ternary oxides by APS.

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.

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.

Influence of added La2O3 on the microstructure, mechanical properties, and tribocorrosion resistance of TiB2–Ni plasma-sprayed coatings

To enhance the tribocorrosion resistance of 7075-T6 aluminum alloy in deep sea environments, TiB2–Ni coatings with varying La2O3 content were deposited on 7075-T6 aluminum alloy substrates using plasma spray technology. The effects of different La2O3 contents on the organization, structure, and properties of the coatings were analyzed. The results indicated that La2O3 incorporation suppressed brittle phase formation such as Ni3B; 1.0 wt% La2O3 addition reduced Ni3B by 16.9%. The coating's corrosion resistance significantly improved with La2O3 doping - the self-corrosion current density of the 1.0 wt% La2O3-doped coating decreased from 71.2 nA/cm2 to 30.2 nA/cm2.

Study on microstructure and thermal shock resistance of plasma sprayed Cr2O3/8YSZ composite coating

In order to explore the high temperature performance of Cr2O3/8YSZ composite coating, four kinds of Cr2O3/8YSZ composite coatings were prepared on the surface of Q235 steel by using the plasma spraying technology (the content of 8YSZ is 50%, 30%, 20% and 0%, respectively). The morphology of the coating was characterized through thermal field emission scanning electron microscopy, and the distribution of elements in the section of the coating was scanned by using EDS line. The phase composition of the composite coating was analyzed by using X-ray diffractometer, and the surface roughness of the composite coating was measured by using surface profilometer. The microhardness of the coating was measured by using automatic micro-Vickers hardness tester, and the scratch resistance of the coating was compared by using scratch tester. The thermal shock resistance of the coating was tested in Gleeble-3800 thermal physical simulator, and the cross section morphology after thermal shock was observed and analyzed. The results show that when the ratio of Cr2O3 to 8YSZ is 7∶3, the sample coating has good thermal shock resistance due to the deflection effect of 8YSZ on the vertical cracks and the thermal stress release effect of the pores and cracks in the coating.

Study on the performance of GDC electrolytes fabricated by atmospheric plasma spraying and vacuum plasma spraying

For metal-supported solid oxide fuel cells (MS-SOFCs), gadolinium-doped ceria (GDC) is one of the most promising electrolyte materials due to its high ionic conductivity. The plasma spraying technique has unique advantages in the preparation of MS-SOFCs, such as high efficiency, low cost, and low thermal impact on the metal support. However, few studies have been conducted on the preparation of dense GDC electrolytes using plasma spraying technology. In addition, it is not clear whether the composition and Ce valence state of GDC change during the plasma spraying process. In order to investigate this issue, GDC electrolytes were fabricated by atmospheric plasma spraying (APS) and vacuum plasma spraying (VPS) techniques. It is found that the GDC electrolyte fabricated by VPS is denser and has better electrochemical performance. The open circuit voltage and maximum power density of the VPS-cell at 600 °C are 0.90 V and 175.7 mW/cm2, respectively, while those of the APS-cell are 0.86 V and 124.8 mW/cm2, respectively. Moreover, the valence state of Ce4+ in the GDC electrolyte remains unchanged after plasma spraying, while the composition of Ce/Gd changes. This work successfully fabricates GDC electrolytes with qualified performance and provides a reference for further optimizing spraying parameters to prepare high-performance MS-SOFC.

CMAS corrosion resistance of YSZ thermal barrier coatings with Al2O3 and YSZ-Al2O3 protective layers

Molten calcium-magnesium-alumina-silicate (CMAS) corrosion has become a major constraint for the application of YSZ thermal barrier coatings (TBCs). In this paper, Al2O3 and YSZ-Al2O3 protective layers with a thickness of 50 μm were prepared on the surface of 8YSZ TBCs using air plasma spraying technology, and the progressive damage modes of the different TBCs under CMAS exposure were investigated, and the effects of the composition and microstructure of the protective layers on the infiltration and wetting behaviour of CMAS were compared. When the exposure time was shorter, the dense YSZ-Al2O3 had a better impermeability barrier effect. As the interaction time between CMAS and the coating was prolonged, the structure and phase stability of YSZ-Al2O3 were damaged, the thickness was thinned, and Al2O3 had better stability and showed better protective effect. CMAS wettability was mainly related to the roughness of the coating surface, and the wettability was poorer on rough surfaces.

CMAS Corrosion Resistance of Plasma-Sprayed YSZ and Yb2O3-Y2O3-Co-Stabilized ZrO2 Coatings under 39–40 KW Spraying Power

This study uses atmospheric plasma spraying (APS) technology to prepare thermal barrier coatings (TBCs) with yttrium-stabilized zirconia (YSZ) and Yb2O3-Y2O3-co-stabilized ZrO2 (YbYSZ) materials at different spraying powers. It analyzes the differences and changes in the microstructure, thermodynamic properties, and mechanical properties of the TBCs. The CaO-MgO-Al2O3-SiO2 (CMAS) resistance of coatings was tested using thermal cycling-CMAS experiments and isothermal corrosion experiments. Compared to YSZ coatings, YbYSZ coatings have lower thermal conductivity, a higher hardness and elastic modulus, a longer lifetime under thermal cycling-CMAS conditions, and lower penetration and degradation depths. Under thermal cycling-CMAS coupling conditions, the optimal power range for the longest thermal cycling lifetime for both coatings is 39–40 kW. Overall, compared to the YSZ material, the YbYSZ material exhibits superior properties.

Tribological properties of atmospheric plasma sprayed Cr3C2–NiCr/20% nickel-coated graphite self-lubricating coatings

Using atmospheric plasma spraying technology, Cr3C2–NiCr (CN)and Cr3C2–NiCr/20 % Nickel-coated graphite (CG) composite coatings were successfully deposited on 304 stainless steel substrates, with three different spraying distance parameters designed to optimize the experiment. The study investigated the influence of nickel-coated graphite on the structure, hardness, porosity, and friction-wear performance of the composite coatings. Wear mechanisms were investigated based on analyses of morphologies and chemical states of the worn surfaces of the CG composite coatings. Our results demonstrate that the CG coating exhibits lower friction coefficients, ranging from 0.24 to 0.28, than that of the CN coating. The incorporation of nickel-coated graphite leads to formation of a solid-lubricating film at friction interface, lowering friction and wear. What's more, presence of nickel-coated graphite mitigates brittleness of the CN coating, as is deemed important for improving abrasion resistance of the coatings.

The Innovation in Air Plasma Spray for Hardfacing

Thermal spray coating plays a significant role in industry. The wear-resistant deposition helps to provide a longer life cycle for the components. There is an ongoing effort to develop coatings that improve the coefficient of friction. Compared with other deposition techniques, plasma spray coating can be recommended for a wide range of substrate materials to produce a stable, wear-resistant material. The plasma-sprayed deposition not only improves tribological performance but also embeds the desired mechanical and physical properties. In plasma spray technology, the inert gas used is mostly plasma jet. To create the wear-resistant coatings, the engineers apply self-flux or cermet powder, both of which are expensive materials. Some positive results of deposition using the amorphous powder encouraged the engineers and researchers. But in a few of the investigations on the air plasma spray Fe-based powder, the plasma generation gas is ordinary air. This innovation served to save on production costs. The aim of this work is the study of Fe-based spraying, applying the modification of a plasma torch. Both of the innovations help to enhance the hardfacing effect for wear resistance.

Microstructure and tribological properties of Al-30Si-5Cu composite coating reinforced with ceramic phases synthesized in situ by plasma spraying

For improving the wear resistance of Al-30Si-5Cu coating, in this study, the composite coating in-situ synthesized TiC-TiN-TiN0.8C0.2/Al-30Si-5Cu (TiCN/Al-30Si-5Cu) was prepared used TiH2-graphite aggregates as raw materials and plasma spraying technology. The effect of in-situ synthesized ceramic reinforcements on the coating was researched in detail. The results showed that during the plasma spraying process, TiH2 decomposed and chemically reacted with graphite to form TiC. Additionally, some Ti also reacted with N2 and O2 in the air to form TiN and TiO2. The phases composition of TiCN/Al-30Si-5Cu composite coating were α-Al, β-Si, θ-Al2Cu, β-Ti, TiC, TiN, TiN0.8C0.2, TiO2, as well as amorphous CNX and residual graphite. The TiC-dominated ceramic phases and β-Si were uniformly distributed in the coating, which were tightly bound to the α-Al matrix. Because of the exceptionally rapid cooling rate during the coating preparation, a minor amount of submicron Si particles were also generated. The microhardness, elasticity modulus, and fracture toughness of TiCN/Al-30Si-5Cu composite coating appeared improvements compared to those of Al-30Si-5Cu coating. The TiCN/Al-30Si-5Cu composite coating exhibited smoother friction coefficient curve, along with lower friction coefficient and wear volume in comparison to the Al-30Si-5Cu coating. This suggested that the ceramic reinforcing phases in-situ synthesized led to a notable advancement in the wear resistance of the TiCN/Al-30Si-5Cu composite coating. The wear resistance of TiCN/Al-30Si-5Cu composite coating demonstrated an increasement of 78.3 % over the substrate and 28.2 % over the Al-30Si-5Cu coating. Under the dry friction test conditions outlined in this study, the wear mechanism of the TiCN/Al-30Si-5Cu composite coating included abrasive wear and fatigue wear, coupling with a minimal amount of oxidative wear.

A novel plasma-sprayed Cr/FeCrAl dual-layer coating on Zr alloy for potential high‐temperature applications

To better meet the requirements in loss-of-coolant accidents (LOCA) and conventional operating conditions in nuclear applications, this work prepared Cr, FeCrAl, and Cr/FeCrAl composite coatings on Zr alloys using plasma spraying technology. The microstructures, hardness, and high-temperature oxidation resistance of coatings are examined. The high-temperature oxidation of coatings was conducted at 1200 °C in air for 20, 40, and 60 min. All coatings exhibited characteristic lamellar microstructures accompanied by small pores. The inner layers of the coatings, benefiting from the “compacting effect” of subsequently deposited particles, displayed lower porosity and higher hardness. The order of high-temperature oxidation resistance among the coatings was determined as follows: Cr/FeCrAl coating > Cr coating > FeCrAl coating. Notably, the Cr/FeCrAl composite coating demonstrated exceptional durability even after a 60-min exposure, with no ZrO2 formation and negligible Fe and Cr diffusion. However, oxygen could still reach the Zr substrate due to inherent pores and the lamellar structure in the as-sprayed coatings. Therefore, post-treatments are suggested to mitigate or eliminate these pores, thereby improving high-temperature oxidation resistance.

Effect of La2O3 on hardness, wear resistance and corrosion resistance of WC/Fe90 iron-based composite coatings

In this paper, WC/Fe90 iron-based composite coatings were prepared using plasma spraying technology. The influence of rare earth oxide La2O3 on the microstructure and properties of the composite coatings was studied through microstructural characterization, phase identification, microhardness, wear resistance, and corrosion resistance. The results showed that the composite coatings were mainly composed of α-Fe, M7C3, Fe-Cr, FexCy, and other reinforcing phases. The addition of La2O3 promoted the decomposition of WC particles and improved the uniformity of the coatings. When the La2O3 content reached 1.0 wt%, the hardness was the highest, reaching 885.481 HV, which was 10% higher than that of the untreated coatings. The addition of La2O3 increased the friction coefficient but still improved the wear resistance. Compared to the coatings without La2O3, the mass loss due to wear was reduced by approximately 40%. Moreover, the addition of La2O3 formed a passive film on the surface of the coatings, effectively preventing the penetration of Cl- ions and refining the grain structure of the coatings, significantly enhancing the corrosion resistance. When the La2O3 content was 1.0 wt%, the corrosion resistance of the coatings was the best.

Material system and tribological mechanism of plasma sprayed wear resistant coatings: Overview

Challenging environments in aviation, automotive, electric power, and various industrial sectors are increasing industry and technological demands, resulting in machine damage and energy loss from friction and wear between interacting surfaces. Addressing this issue requires the development of new and advanced materials, processing techniques, and surface modification methods to enhance performance and reduce friction and wear. Plasma spraying technology is essential for material surface reinforcement and modification because of its low cost and stability. This paper reviews and summarizes the research progress on plasma spraying wear-resistant coating material systems and tribological mechanisms, covering the working process and principles of plasma spraying equipment. It also details wear-resistant coating material systems, including iron-based, nickel-based, copper-based, other metal materials, oxides, and monoxide ceramic materials.Furthermore, it addresses the wear-resistant and friction-reduction mechanisms of wear-resistant coatings, aiming to summarize the tribological strengthening mechanism concerning wear resistance and friction reduction. Moreover, this paper covers aspects such as powder design, sealing treatment, laser remelting, and other methods for regulating the wear resistance of coatings, examining their influence on the wear resistance of coatings in material design, spraying process, and post-spraying treatment. Plasma spraying wear-resistant coatings should be used along with doping modification and other methods to study the new spraying materials; furthermore, the optimization of the spraying process and post-treatment methods should be investigated to prepare a wear-resistant coating that meets the performance of the actual working conditions. At the same time, ultrahigh temperature wear-resistant coatings and super lubricating coatings are also future research priorities. In addition, when comparing plasma transfer arc spraying technology and plasma enhanced high-speed arc spraying technology with plasma non-transfer arc spraying technology, the jet temperature is higher, and the cost is lower; however, since the process is still in its infancy, the follow-up should be strengthened in this area of technical research. This paper provides a theoretical basis and reference for researching plasma spraying wear-resistant coatings in various fields.

Enhancing the microwave absorption performance of graphite/Al2O3 composites through manipulating sheet resistance

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

Thermal shock resistance of a novel (Gd1/6Tb1/6Dy1/6Tm1/6Yb1/6Lu1/6)2Si2O7 environmental barrier coating

AbstractMulticomponent rare earth (RE) disilicates have been recognized as promising candidates for environmental barrier coatings (EBCs). In this work, a novel EBC system with (Gd1/6Tb1/6Dy1/6Tm1/6Yb1/6Lu1/6)2Si2O7 as top coat and Si as bond coat was deposited on SiC‐based substrates by atmospheric plasma spraying technology and subjected to 200 thermal shock cycles at 1350°C. The composition and microstructure evolution in the coating during thermal cycling were investigated using x‐ray diffraction analysis and scanning electron microscopy. The results show that the as‐prepared EBC remains dense and integrated, and no obvious spalling or penetrating cracks could be observed in the coating after 200 thermal shock cycles. Furthermore, the average thickness of thermal growth oxide layer between (6RE1/6)2Si2O7 top coat and Si bond coat is 0.71 ± 0.17 µm and 0.98 ± 0.23 µm before and after the thermal cycling, respectively, indicating the excellent thermal shock resistance of (6RE1/6)2Si2O7 EBC. The present study presents a novel EBC with excellent thermal shock ability and is expected to contribute to the development of EBC for advanced SiCf/SiC ceramic matrix composites.