Plasma Spraying Of Powders Research Articles

Effect of efficient structural tuning on the microstructure, corrosion resistance, and wear performance of AlCoCrFeNi/AT13 composite coatings

This study developed a rapid structure control technique for AlCoCrFeNi/AT13 (Al₂O₃–13 % TiO₂) composite coatings using plasma spraying and dual powder feeding. Four coatings were fabricated: pure HEA, HEA-D (dispersed), HEA-S1 (multilayer with outer HEA), and HEA-S2 (multilayer with outer AT13). The introduction of AT13 altered the internal stress distribution and enhanced corrosion resistance by lowering the electrochemical reaction rate. In layered coatings (HEA-S1, HEA-S2), the AT13 interlayer barrier reduced corrosion tendency. Additionally, pure HEA coatings exhibited adhesive wear. While HEA-D coatings experienced abrasive wear as AT13 particles improved plastic deformation and interface shearing. HEA-S1 reduced strain and wear via an internal AT13 layer. HEA-S2 achieved superior abrasion resistance through an outer AT13 layer, exhibiting typical abrasive wear mechanisms.

ОЦЕНКА ВЛИЯНИЯ РЕЖИМОВ ШЛИФОВАНИЯ НА ШЕРОХОВАТОСТЬ ПЛАЗМЕННЫХ ПОКРЫТИЙ

The equipment for laboratory tests during grinding of plasma coatings is presented. The results of the study of the influence of the modes of mechanical treatment with an abrasive tool on the quality of the surface of plasma coatings are presented. Three materials were applied to the surfaces - based on iron, nickel and self-fluxing powder for plasma spraying, with their subsequent grinding and study of the surface quality.

Synthesis, Characterization of Chromium Oxide Powders and Coatings

The chromium oxide powders are transformed into plasma sprayable particles by using synthetic polymers for agglomeration. In order to carry out the agglomeration process, spray drying technique was employed. This research work highlights the significance of the process variables that control the synthesis of plasma spray powder and consequently, the properties that were suited for plasma spray coating. Energy Dispersive Spectroscopy (EDS) was used to characterize the elemental composition, while scanning electron microscopy (SEM) was used to analyse the morphology and powder grain sizes and X-ray diffraction (XRD) was used to identify the phase structure. And for the development of coatings on the substrates, Atmospheric plasma spray (APS) technique was used. The plasma sprayable powders were created with the intention of investigating for use as corrosion-resistant coatings.

Characterisation of thin α-Al2O3 tribo-coating deposited by low-power gas tunnel plasma spray

This study used a unique, low-power (2.8 kW) gas tunnel plasma spray and γ-Al2O3 feedstock powder to deposit a thin Al2O3 coating (<2 µm) on mild steel substrate. By optimising the plasma gas flow rate, powder feed rate, spraying time, and distance, a dense and homogeneous Al2O3 coating was obtained at a very high deposition rate (150 nm/s). During plasma coating, the high energy density plasma transforms the γ-Al2O3 powder into a highly crystalline α-Al2O3 as the predominant microstructure of the coating. The performance of the Al2O3 coating on mild steel was then evaluated preliminary using a linear sliding wear test against a chrome-steel ball, with the results indicating an 18–26% reduction in wear when compared to the uncoated substrate.

Deposition and characterization of plasma sprayed NiTi powder on stainless steel and graphite substrate

The surface behavior of the NiTi coating has been studied by composition analysis, microstructure, and interface diffusion. The shape memory effect was investigated by thermal recovery of the indented surface at various loads. Near the theoretical density (99.3%), high Vickers hardness 244–310 HV, was measured by applying various loads of 1961–98 mN for NiTi samples separated from graphite substrate. However, samples prepared from stainless steel substrate display more homogenous hardness at various loads from 214 to 238 HV with applied load from 98 to 490 mN. Phase transformation temperatures indicated that above 105 °C, the alloy transforms and is saturated in the austenite stage. Both samples exhibited a hysteresis effect of shape memory effect on bending mode in thermal cycles. Both samples were indented at various loads from 98 to 1961 mN load for 10 s, and residual indent points are imaged. Recovery in the depth of indent points was analyzed after heating samples above austenite finish temperature at 150 °C for 10 min. A maximum recovery of 77% is achieved in the sample retrieved from stainless steel substrate at 245 mN load.

Microstructure evolution and reaction mechanism of reactive plasma sprayed Ti–C–N coatings

This investigation focuses on the feasibility of the reaction synthesis of Ti–C–N phase using plasma spraying powder mixture of Ti and graphite under nitrogen ion flame flow. To regularize the microstructure and properties of the sprayed Ti–C–N coating, the microstructure evolution of the Ti-graphite-N2 system was analyzed based on water quenching tests. The reaction pathway of the Ti-graphite-N2 system has been investigated by thermodynamic calculations and thermal analysis, revealing the mechanisms of the reaction during plasma spraying. The results show that the as-deposited coatings exhibit a typical layered structure consisting mainly of TiCxNy and TiO2. The quenched powders exhibit a melting process from irregular particles to smooth spherical particles, forming complete droplets with increasing spray distance. Based on phase evolution of the quenched powders and the thermal analysis of Ti powders or Ti/graphite powders under N2/Ar atmosphere, it found that the Ti powder can reacted with graphite or N2 by solid-solid or solid-gas reaction to form TiCx and TiNy, and TiNy can be formed preferentially as compared with TiCx phase. As the spraying distance increases, the Ti and graphite reactions are enhanced, and a pronounced TiCx phase can be detected once a large liquid Ti phase is formed. As the spray distance increases, formed TiNy and TiCx phases aggregate into droplets and rapidly transform into TiCxNy phase by solid-solution reactions. In addition, titanium oxide coexists in lamellae of Ti–C–N coatings due to the absorption and dissociation of O₂ from the atmosphere at the droplet surface.

Improving the flowability of fine WC-12Co powder using atmospheric pressure nitrogen microwave plasma torch treatment

WC-Co powders are mainly used in thermal spray coatings, which improve corrosion and wear resistance as well as the regeneration capacity of damaged components. The use of fine powders in the thermal spray coating process is essential to form a dense coating layer. However, fine powders possess poor flowability due to their morphology and van der Waals forces between particles. These characteristics limit their application in thermal spray coatings. In this study, a nitrogen microwave plasma torch was applied to WC-12Co powder (D50 = 20 μm) to improve the flowability of the powder. The rough surface of the particle was melted and changed to a smooth, spherical surface. As a result, the flowability of the plasma-treated powder improved significantly from 0 to 4.02 g/s. Thus, a microwave plasma torch improves the flowability of fine WC-12Co powders and is suitable for continuous treatment and mass production of plasma spray powders.

Reaction and growth mechanisms of MoO3-Al system in plasma spraying

To regulate the microstructure and properties of the composite coating prepared by plasma spraying MoO3-Al composite powder, the microstructure evolution of plasma sprayed MoO3-Al composite powder was analyzed based on water quenching test. The reaction path of MoO3-Al was investigated by thermodynamic calculation and thermal analysis, and reaction and growth mechanisms of the MoO3-Al composite powder during plasma spraying were revealed. The results show that the reaction of MoO3-Al in the plasma jet results in formation of main phases Mo and Al2O3. Due to the phase separation structure characteristic resulted from gravity segregation, the Mo phase grew into submicron cellular particles and the Al2O3 phase grew into a dense structure during the solidification process. Mo4O11 and Al2(MoO4)3 are important intermediate products in the reaction between MoO3 and Al.

Processing of solid lubricant doped ceramic powder feedstock using heterocoagulation technique for plasma spraying

In this study, a novel technique called heterocoagulation was employed to fabricate solid lubricant doped ceramic matrix composite powder for plasma spraying. Zeta potential of all the ceramic materials (Al₂O₃, TiO2, YSZ, Cr2O3, and Al₂O₃-TiO₂), solid lubricants (hBN, WS2, MoS2, BaF2, CaF2) with and without surfactants, and heterocoagulated powders were measured. Effective heterocoagulation occurred for Al₂O₃/BaF₂, YSZ/WS₂, YSZ/BaF₂, Al₂O₃-TiO₂/WS₂, and Al₂O₃-TiO₂/BaF₂ composites. The composite powders were characterized using SEM and XRD. The wettability test of BaF2 and CaF2 with ceramic materials revealed that Al₂O₃, Cr₂O₃, and Al₂O₃-TiO₂ were highly wettable by CaF2. Whereas, BaF2 displayed excellent wetting characteristics with all the ceramic coating layers. From the zeta potential and wettability results, YSZ can be selected as the ceramic matrix, and WS2 and BaF2, respectively as low and high-temperature solid lubricants for plasma spraying.

Photocatalytic activity of Zn2SnO4 coating deposited by air plasma spraying

In the present research study, zinc stannate was synthesized using high energy mechanical milling of zinc oxide and tin oxide powders with a molar ratio of 2:1, respectively. The synthesized Zn2SnO4 feedstock powder was deposited on a 316 stainless steel plate by atmospheric plasma spraying. X-ray diffraction, Fourier Transform Infrared (FT-IR) analysis, Scanning electron microscope (SEM) and UV–Vis diffuse reflectance spectroscopy (DRS) were used for the phase analysis, analysis of patterns of vibration, evaluation of micrographs and photo-absorption ability, respectively; and methylene blue solution with a concentration of 6 mg/L was used to study the photocatalytic activity of the plasma-sprayed Zn2SnO4, and it was compared with those of the plasma-sprayed ZnO and the plasma-sprayed SnO2 as its binary counterparts. The band gap energy of plasma sprayed Zn2SnO4 and Zn2SnO4 feedstock powder were 3.1 and 3.6 eV, respectively. Zn2SnO4 coating also showed higher photocatalytic activity than that of SnO2 coating. It was concluded that although plasma spraying could be used as a promising method to deposit Zn2SnO4, further attempts are needed to enhance its light-harvesting and photocatalytic efficiency.

Optimization of Yb2O3-Gd2O3-Y2O3 Co-Doped ZrO2 Agglomerated and Calcined Powders for Air Plasma Spraying

Yb2O3-Gd2O3-Y2O3 co-doped ZrO2 (YGYZ) is considered to be a promising material in thermal barrier coating (TBC) applications. In this study, 2Yb2O3-2Gd2O3-6Y2O3-90ZrO2 (mol.%) (10YGYZ) feedstock candidates for air plasma spraying (APS) were prepared by calcination of agglomerated powders at 1100, 1200, 1300, 1400, and 1500 °C for 3 h, respectively. Incomplete solid solution was observed in calcined powders at 1100, 1200 and 1300 °C, and the 1500 °C calcined powder exhibited poor flowability due to intense sintering effect. The 1400 °C calcined powders were eventually determined to be the optimized feedstock for proper phase structure (cubic phase), great flowability, suitable apparent density and particle size distribution, etc. 10YGYZ TBCs with the optimized feedstock were prepared by APS, exhibiting pure c phase and good chemical uniformity. Controllable preparation of coatings with different porosity (i.e., 7%–9% and 12%–14%) was realized by stand-off distance adjustment.

Керметные плазменные покрытия TiC – Cr3C2 – WC – NiCr – Mo – C

Two bulk cermets TiC – WC – Cr3C2 – Ni 20 % Cr – Mo – 2.8% C after liquid-phase sintering at 1400 °C for 1 hour were used to manufacture powders for plasma spraying of coatings. Cermets were obtained with limited time of mechanical alloying at the stage of mixing. Plasma coatings were sprayed on a setup with a nozzle attached to a plasmatron for local protection of the sprayed particles from the air atmosphere. The content of WC – Cr3C2 – C in the cermets provided compensation for carbon losses at all stages of coating production and the formation of an annular zone, the volume of which determines the increase in the TiC content in the coatings by 20 % and the formation of additional carbides in the matrix. The microhardness of cermet with an initial carbide content of 60% is 15.26 – 16.83 GPa with a load on the indenter of 200 G and 20.91 – 24.68 GPa with a load on the indenter of 20 G, the difference was explained by a scale factor. The contribution of the microhardness of carbides to the microhardness of cermet with an initial carbide content of 60% was estimated according to the rule of mixtures, proceeding from their volume fraction and microhardness of cermet under a load on the indenter of 20 G. In the initial powder for spraying, this contribution is high, 33.19 GPa, close to Hardness TiC. The contribution of microhardness of carbides in the coating is lower, 28.09 GPa.

Spray dried nano oxide ceramics for free flowing plasma spray coating powders and battery material processing

Advanced materials are widely used in electronics, aerospace and automobile industry devices and also in substances synthesized for food, medical and pharmaceutical industries. The quality of the base material powder has high influence on the resulting material body (the product) which goes into the manufacture of the device. To name a few (a) flowable ceramic powders from agglomerated nano ceramic powders for plasma spray coatings with the right sprayable powder characteristics (b) advanced graphene encapsulated nano ceramic oxide powders with uniform conductive coating layers as promising electrodes in Li-Ion batteries, (c) advanced bio-ceramic oxides such as hydroxy-apatite ceramic materials with right amounts of moisture, density and composition consistency as bone and dental implants in bio-ceramics research are examples. Among the many processing methods to achieve the base powders from nano ceramic raw materials the most capable and efficient is ‘Spray Drying’ which results in powders with high purity with well-defined properties. Complex composite by spray drying is achieved where the ‘matrix host’ material is encapsulated by the ‘guest layer’ with special properties. This paper illustrates results pertaining to experimentation via spray drying and microscopic investigation by using SEM associated with EDS on (a) Yttria stabilized zirconia plasma sprayable powders for Thermal Barrier Coatings application and (b) nano yttria stabilized zirconia incorporated into microns sized alumina powders for enhanced densification, to understand the significant role of process parameters on uniformity and consistency of the spray dried products. Information based on review on spray dried Li-ion battery materials is also included.

STRUCTURE AND PROPERTIES OF Fe-B-C POWDERS ALLOYED WITH Cr, V, Mo OR Nb FOR PLASMA-SPRAYED COATINGS

In the present study, the microstructure development and properties of the starting Fe-B-C powders for plasma spraying fabricated by dispersing a consumable rotating rod were investigated as functions of alloying elements additions. These powders were prepared in the following compositional ranges: B (10…14 wt.%), C (0.01…0.5 wt.%), Me (0…5.0 wt.%), where Me – Cr, V, Mo or Nb, balance Fe. Structural properties were characterized by etallography, X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. Mechanical properties of the powders were measured by a Vickers indenter. Compression strength, oxidation resistance, and melting temperature were also determined. Chromium or vanadium were found to dissolve completely in Fe2(B, C) and Fe(B, C) constituent phases of the Fe-B-C powders replacing iron and forming substitutional solid solutions. By entering into the iron borides structure, these alloying elements improve ductility and oxidation resistance but lower melting temperature and hardness of the powders. Molybdenum or niobium were mainly found in secondary phases such as Mo2B, Mo2(B, C) or NbB2 at the Fe2(B, C) boundaries. As a result, these alloying elements enhance hardness, oxidation resistance and melting temperature of the powders.

Recycling of Alumina Power After Plasma Spraying

The possible reuse of powder Al2O3 waste formed in manufacturing of ceramic refractory products by plasma spraying was studied. The powder alumina waste was found to be individual particles α- and γ-Al2O3 and their conglomerates and also included iron oxides in the form of Fe2O3 and Fe3O4. It was shown that the plasma-spraying powder waste had to be purified of Al2O3 conglomerates and iron oxides in order to reuse it. For this purpose, powder waste should be sifted through a sieve and subjected to magnetic separation. It was established experimentally that such a powder can be reused for applying coatings and fabricating products by plasma spraying without degrading their quality

Tribological properties of plasma sprayed zircon-alumina powder mixture with and without laser re-melting

ABSTRACTThis investigation focusses on the wear mechanism of as-sprayed and laser treated mullite based coatings, produced by plasma spraying, under sliding wear condition. First, an alumina powder and zircon sand mixture was plasma sprayed to produce a mullite coating. Selected as-sprayed coatings were subsequently laser treated. The tribological performances of both as-sprayed and laser re-melted coatings were assessed using a pin-on-disc wear apparatus. Hardened steel and WC-Co balls served as rubbing counterparts. A plasma sprayed alumina coating was used for bench marking purposes. Plastic deformation was the dominant wear mechanism under low load-low speed condition for both as-sprayed and laser treated coatings. However, at higher loads and speeds the coatings were found to undergo micro-fracture followed by pulverisation. Wear resistance of the coatings improved following laser treatment.

Structure and Wear Resistance of the Coatings Plasma Sprayed with “TiC + High Chromium Cast Iron Binder” Composite Powder

A metal matrix composite material was obtained by self-propagating high temperature synthesis (SHS) from powder mixtures of titanium, carbon (carbon black), and high chromium cast iron of PG-S27 trademark. Synthesized products were crushed and sieved to get a composite powder for plasma spraying of wear resistant coatings. The coatings were tested for hardness and abrasive wear resistance. According to X‑ray diffraction and scanning electron microscopy investigation, the structure of coatings involved fine TiC particles uniformly distributed over the cast iron matrix. It was ascertained that the coatings plasma sprayed with the SHS composite powder had a hardness 2 times greater and abrasive wear resistance 3.5 times greater than that of plasma sprayed with the cast iron powder.

One-Step Deposition of Polyester/TiO2 Coatings by Atmospheric Pressure Plasma Jet on Wood Surfaces for UV and Moisture Protection

In this work, polyester/TiO2 coatings on wood surfaces were prepared in one step via two deposition methods by using an atmospheric pressure plasma jet technique with the aim to further enhance the stabilization of the wood surfaces against UV-radiation and moisture. The first method, based on the combination of plasma spray powder (PSP) coating and liquid precursor plasma spraying (LPPS) coating techniques, used polyester powder and titanium tetraisopropoxide (TTIP) liquid precursor as feedstock. In the second method, the polyester/TiO2 coatings were prepared by using a mixed powder of polyester micro-particles and TiO2 nano-particles as feedstock and applied via plasma spray powder coating technique. The surface topology and morphology of the wood samples were observed by scanning electron microscopy (SEM). The SEM results showed the presence of a rough structure after coating with polyester/TiO2. The surface chemical compositions of the samples were characterized by X-ray photoelectron spectroscopy and by Fourier transform infrared spectroscopy. The wetting behaviour of the coated wood surfaces was studied by measuring the water contact angle. After coating a hydrophilic wood surface with polyester/TiO2 prepared via (PSP + LPPS), it showed excellent water repellency; the wood surfaces were transformed from hydrophilic to superhydrophobic, while the polyester/TiO2 coating prepared via (PSP) was hydrophilic. Protection against UV radiation-induced colour changes was determined by UV tests and photo-assisted analysis using the CIELab colour system. The abrasion test results indicated that the polyester-containing films had good abrasion resistance and good adhesion to the wood substrates.

Synthesis of Yttria-Stabilized Zirconia Nano Powders for Plasma Sprayed Nano Coatings

Abstract Plasma sprayed Yttria Stabilized Zirconia (YSZ) coatings, with few microns sized microstructure/grain morphology has been well researched, reported and established as an industrial Thermal Barrier Coatings (TBC) material/system. However, nano structured YSZ coatings possess improved characteristics when compared with their micron sized counterparts. However, due to their nano sizes, light weight, and low density, plasma spray coating process of nano powders suffers from flowability issues due to lack of nano powder inertia/momentum, leading to poor deposition/ uneven coating thickness. In this research work, nano structured YSZ coatings were synthesized by using an Atmospheric Spray Coating (APS) facility. Nano powders of YSZ were used as the starting materials to prepare micron sized plasma sprayable powders. 80μm thick NiCrAlY bond coat (commercial) and 200μm thick YSZ top coat with nano microstructure (lab synthesized) were built on steel substrates. The starting nano crystalline (YSZ) powders, measuring 30-70 nanometers (nm) were synthesized in the laboratory via chemical method (sol-gel) by employing zirconium oxy chloride hexa-hydrate and yttrium nitrate as precursors, citric acid as chelating agent and ethylene glycol for the diversification reaction followed by calcination @ 1000°C. They were then re-constituted into micron sized (53-106 μm) plasma sprayable powders by agglomerating with polyvinyl alcohol (PVA) binders. The nano crystallite morphology of powders and coatings were analyzed by Scanning Electron Microscope (SEM), chemical composition by Energy Dispersive spectroscopy (EDS) and crystal structural phase by X-ray diffraction (XRD). The influence of calcination temperature of 1150°C on nano crystallite morphology was also studied.

Керметы на основе TiC для плазменного напыления

The microstructure and microhardness of eleven volumetric cermets based on TiC carbide with nickel and cobalt based matrices after liquid-phase sintering at a temperature of 1400 °C were studied. It is supposed to use the research results for the subsequent formation of a powder for plasma spraying of coatings. The compositions of the matrix, additional hardening phases, and carbon were selected taking into account the specific features of the formation of plasma coatings: a decrease in the carbon content and high solidification rates of the sprayed particles with the formation of additional nanosized carbides and an increase in the volume fraction of carbides from 70 % to 88 %. As the matrix, we used the traditional composition for cermets with TiC carbide, NiCr – Mo, and industrial powders, PGSR brands, Ni – 13.5 Cr – 2.7 Si – 4.5 Fe – 0.37 C – 1.65 B, and TAFA 1241F Co – 32 Ni – 21 Cr – 8 Al – 0.5 Y. The ring zone on TiC carbide is formed with the participation of WC, Cr3C2, TiN, matrix phases and additional carbon in the composition of cermets, 1 – 2.8 %, as a result, the initial volume fraction of TiC carbide increases 70 to 88 %. Additional carbon is consumed to reduce oxygen content at the stage of sintering (reduction of oxides). After sintering, cermets have high microhardness values at a load on an indenter of 20 G, 1940 – 3210 kgf/mm2, and lower values at a load on an indenter of 200 G, which was explained by a scale factor. The maximum calculated contribution of the hardness of the hardening phases to the hardness of the cermet was established for cermets with a Co matrix of 3681 kgf/mm2.