Atmospheric Plasma Spray Technique Research Articles

Fabrication of Direct Oxidation Solid Oxide Fuel Cell Anodes Using a Novel Atmospheric Plasma Spraying Technique

Composite coatings of CuO and samaria-doped ceria (SDC) have been fabricated by atmospheric plasma spraying using a combination of suspension and dry-powder plasma spray techniques. The coatings prepared using this novel hybrid technique demonstrate a finer microstructure than similar coatings prepared using conventional dry-powder methods. The coatings consist of fully-melted and partially-melted phases of both CuO and SDC. During deposition, a large portion of the CuO was reduced to Cu2O. The influence of processing conditions on deposition efficiency and porosity were investigated, with a plasma power of 77 kW leading to a maximum in coating porosity. Improvement of the dispersion of the CuO suspension by adjusting the pH led to a finer network of CuO particles in the fabricated coating.

Properties of tungsten coating deposited onto copper by high-speed atmospheric plasma spraying

Tungsten (W) coatings were fabricated on copper (Cu) by high-speed atmospheric plasma spray (HAPS) technique. The properties of the porosity, oxygen content, bonding strength and microhardness were measured. The results obtained indicated that the HAPS-W coating showed good properties particularly in terms of porosity and oxygen content. The porosity of the HAPS-W coating was 2.3% and the distribution of pore size diameter was mainly concentrated in the range of 0.01–1 μm. The oxygen content of the coating measured by means of Nitrogen/Oxygen Determinator was about 0.10 wt.%. These initial results suggest that the HAPS-W coating has achieved the reported properties of the vacuum plasma spray (VPS) W coating. Compared with VPS, HAPS-W technique could provide a convenient and low cost way to obtain adequate W coatings for fusion applications.

Sliding wear behavior of plasma sprayed nanoceramic coatings for biomedical applications

This paper reports on the sliding wear performance of the nanostructured Al2O3–13TiO2, ZrO2 and the bilayered (ZrO2/Al2O3–13TiO2) coated biomedical Ti–13Nb–13Zr alloy in simulated body fluid condition. The nanopowders were sprayed using an atmospheric plasma spray technique and the reciprocatory sliding wear behavior of all the above coatings was evaluated using wear testing machine. The bilayered (ZrO2/Al2O3–13TiO2) coating which has not been reported hitherto exhibited two hundred and five hundred fold increase in the wear resistances when compared with that of the nanostructured Al2O3–13TiO2 (AT) and ZrO2 (YSZ) coatings. This substantial improvement in the wear resistance of the bilayered coating is attributed to its lower porosity and higher adhesion strength when compared to the AT and YSZ coatings. This study suggests that this new type of bilayered coating may be a preferred approach to be tried for obtaining much higher

On resultant properties of atmospheric plasma sprayed yttria stabilised zirconia coating deposits: designed experimental and characterisation analysis

In this investigation, yttria stabilised zirconia coatings were deposited by atmospheric plasma spray technique under different levels of power, primary gas flowrates, standoff distances, powder feedrates and carrier gas flowrates as prescribed by the central composite rotatable design matrix. The deposition efficiency test and the porosity test were carried out to study the melting state of the feedstock material. The tensile bond strength test, lap shear bond strength test and microhardness test methods were used to evaluate the mechanical properties of coatings. The microstructure analysis was carried out using optical and scanning electron microscopy. The phase analyses were studied by X-ray diffraction. The spray parameters were optimised using multiobjective response surface methodology to maximise deposition efficiency and mechanical properties. The obtained results revealed that the input power is the most predominant factor, which affects the coating deposit quality followed by standoff distance, primary gas flowrate, powder feedrate and carrier gas flowrate. The effects of spray conditions on the coating properties are elaborately discussed in the manuscript.

Characterization and Corrosion Behavior of Plasma Sprayed Pure and Reinforced HA Coatings in Simulated Body Fluid

To evaluate the corrosion behavior in simulated body fluid pure and 10wt% 80Al2O3-20TiO2 reinforced HA coatings were successfully deposited by atmospheric plasma spray technique on SS-304L substrate alloy. To eliminate non favorable phases on the as sprayed coatings the coatings were heat treated at 700°C and 800°C for post coating heat treatment technique. Both pure and reinforced as sprayed and post coating heat treated coatings were characterized by XRD and SEM/EDAX analysis for surface characterization and further evaluated by electrochemical test for corrosion behavior in simulated body fluids.

A study on sliding and erosive wear behaviour of atmospheric plasma sprayed conventional and nanostructured alumina coatings

Alumina coatings on stainless steel substrate (SS304) were deposited by using atmospheric plasma spray technique with a feed stock of manually granulated and sieved nano Al 2O 3 powder. The hardness, sliding, and erosive wear of the nanostructured alumina coatings (NC) were investigated and compared with that of conventional alumina coatings (CC). Pin-on disc type sliding wear test on the alumina coatings (NC and CC) was performed with load varying from 30 N to 80 N at a sliding speed of 0.5 m/s. Pot type slurry erosion test of the coatings was conducted for different concentrations of Al 2O 3 and a mixture of Al 2O 3 and SiO 2 slurry. The microstructural features of both NC and CC of alumina were characterized by using FE-SEM/EDS and SEM analysis to substantiate the failure of coatings due to wear. Wear and erosion resistance of nano alumina coating is better than the conventional alumina coating as observed in the present work. The bimodal structure of NC contributes for the enhanced wear resistance. The high fracture toughness of NC is due to suppression of cracks by partially melted particles in the coatings.

Study of Substrate Preheating on Flattening Behavior of Thermal-Sprayed Copper Particles

In this study, the effect of substrate preheating on flattening behavior of thermal-sprayed particles was systematically investigated. A part of mirror-polished AISI304 substrates were preheated to 573 and 773 K for 10 min, and then exposed to an air atmosphere for different durations of up to 48 h, respectively. Contact angle of water droplet was measured on the substrate under designated conditions. It was found that the contact angle increased gradually with the increase of substrate duration after preheating. Moreover, smaller contact angle was maintained on the substrate with higher preheating temperature. Commercially available Cu powders were thermally sprayed onto the substrates with the same thermal treatment history as contact angle measurement using atmospheric plasma-spray technique. The splat shape had a transitional changing tendency from a splash splat to a disk one on the substrate with a short duration after preheating, while reappearance of splash splat with the increase of duration was confirmed. In general, wetting of substrate surface by molten particles may dominate the flattening behavior of thermal-sprayed particles. The occurrence of desorption of adsorbed gas/condensation caused by substrate preheating likely provides good wetting. On the other hand, the poor wetting may be attributed to the re-adsorption of gas/condensation on the substrate surface with the increase of duration. In addition, the shear adhesion strength of coating fabricated on blasted AISI304 substrate was enhanced on the once-heated substrate, but weakened with the increase of duration. The changing tendency of the coating adhesion strength and the wetting of substrate by droplet corresponded quite well with each other.

Thermal stability studies of plasma sprayed yttrium oxide coatings deposited on pure tantalum substrate

Plasma sprayed Yttrium oxide is used for coating of crucibles and moulds that are used at high temperature to handle highly reactive molten metals like uranium, titanium, chromium, and beryllium. The alloy bond layer is severely attacked by the molten metal. This commonly used layer contributes to the impurity addition to the pure liquid metal. Yttrium oxide was deposited on tantalum substrates (25 mm × 10mm × 1mm thk and 40 mm × 8mm × 1mm thk) by atmospheric plasma spray technique with out any bond coat using optimized coating parameters. Resistance to thermal shock was evaluated by subjecting the coated specimens, to controlled heating and cooling cycles between 300K to 1600K in an induction furnace in argon atmosphere having ≤ 0.1ppm of oxygen. The experiments were designed to examine the sample tokens by both destructive and non-destructive techniques, after a predetermined number of thermal cycles. The results upto 24 thermal cycles of 25 mm × 10mm × 1mm thk coupons and upto 6 cycles of 40 mm × 8mm × 1mm thk coupons are discussed. The coatings produced with the optimized parameters were found to exhibit excellent thermal shock resistance.

The adhesion strength and indentation toughness of plasma-sprayed yttria stabilized zirconia coatings

In this work, yttria stabilized zirconia (YSZ) coatings were deposited by atmospheric plasma spray (APS) technique under various powder feed rates and spray distances. The microstructure and phase analysis were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Tensile adhesion test (TAT) and interfacial indentation test (IIT) methods were used to evaluate adhesion of coatings. The effect of spray parameters on the coatings adhesion as well as its toughness was investigated. The obtained results revealed that with increasing powder feed rate and spray distance, adhesion of the coatings reaches to a maximum and then reduces. Interfacial toughness values change in the same manner. Adhesion/toughness behaviors of the YSZ coatings were related to microstructural characteristics including the volume fraction and size of pores and unmelted particles.

Sensing properties of atmospheric plasma-sprayed WO 3 coating for sub-ppm NO 2 detection

Tungsten oxide (WO 3) sensitive layers for NO 2 sensors were fabricated by atmospheric plasma spraying technique followed by a heat-treatment. The phase structure and microstructure of the as-sprayed and heat-treated coatings were characterized by X-ray diffraction and scanning electron microscope. The sensing characteristics of these sensors were obtained by measuring the response towards NO 2 in moist air with a concentration in the range of 0–450 ppb and at a working temperature in the range of 95–240 °C. The results showed that the WO 3 coating prepared with low temperature plasma (Ar plasma) had a better sensitivity than the one deposited with high temperature plasma (Ar–H 2 plasma) due to a more porous structure. The obtained WO 3 sensors were found to exhibit different sensing behaviors depending on the working temperature and NO 2 concentration. The electrical resistance of WO 3 sensor increased at high NO 2 concentration in moist air and at a low working temperature. Whereas, it was found that the resistance decreased when the NO 2 concentration was lower than 93 ppb and the working temperature was higher than 130 °C.

Microstructure, bioactivity and osteoblast behavior of monoclinic zirconia coating with nanostructured surface

A monoclinic zirconia coating with a nanostructural surface was prepared on the Ti-6Al-4V substrate by an atmospheric plasma-spraying technique, and its microstructure and composition, as well as mechanical and biological properties, were investigated to explore potential application as a bioactive coating on bone implants. X-ray diffraction, transmission electron microscopy, scanning electron microscopy and Raman spectroscopy revealed that the zirconia coating was composed of monoclinic zirconia which was stable at low temperature, and its surface consists of nano-size grains 30-50 nm in size. The bond strength between the coating and the Ti-6Al-4V substrate was 48.4 + or - 6.1 MPa, which is higher than that of plasma-sprayed HA coatings. Hydrothermal experiments indicated that the coating was stable in a water environment and the phase composition and Vickers hardness were independent of the hydrothermal treatment time. Bone-like apatite is observed to precipitate on the surface of the coating after soaking in simulated body fluid for 6 days, indicating excellent bioactivity in vitro. The nanostructured surface composed of monoclinic zirconia is believed to be crucial to its bioactivity. Morphological observation and the cell proliferation test demonstrated that osteoblast-like MG63 cells could attach to, adhere to and proliferate well on the surface of the monoclinic zirconia coating, suggesting possible applications in hard tissue replacements.

Reduction of Chromium Evaporation with Manganese-based Coatings

The vaporization of Cr-rich volatile species from interconnector materials for high temperature SOFC`s is considered to be a major source of degradation that limits the lifetime of planar SOFC systems [1-6]. For a longer lifetime of these systems, the Cr vaporization of interconnector material shall be reduced [7]. The potential of reduction of the Cr vaporization using coatings with spinel layers is the subject of the present work. In this study the Crofer22APU, IT-11 and F17 TNB interconnector steel is coated with Mn3O4 and (Mn,Co,Fe)3O4 powder as protective layer and LCC10 and LCC13 as contact layer. The coatings were done with wet powder spraying technique (wps) and atmospheric plasma spraying technique (aps). The Cr vaporization rates were studied at 800{degree sign}C in air using the transpiration method. The measured Cr release of the coated samples was compared to uncoated samples. By using Mn3O4 the Cr vaporization rate was found to be 1 order of magnitude lower than uncoated steel. By using (Mn,Co,Fe)3O4 the Cr vaporization rate was found to be 2 orders of magnitude lower than uncoated steel. The Cr-evaporation is depended on the coating technique

Preparation and characterization of aluminum oxide cermet microfiltration membrane using atmospheric plasma spraying

To explore a cost-effective method to fabric inorganic membrane, a cermet membrane is developed as the first attempt in our series studies to prepare macroporous membranes using atmospheric plasma spraying (APS) technique. These membranes consist of α-Al 2O 3 particles in metal binders of Ni and Cr. The effects of plasma power and spraying distance on the performance of the prepared cermet membranes were investigated. Properties of the prepared membranes such as phase transformation, element analysis, structure morphology, pore size, porosity, combination ability and filtration performance were characterized by X-ray diffraction (XRD), energy dispersive X-ray (EDX), scanning electron microscopy (SEM), bubble point test (BPT), binary gray-scale image technique, ultrasonic vibration and dead-end filtration test, respectively. Evaluations of the preparation procedure using APS and comparison of performance characteristics of the prepared cermet membranes with commercial inorganic membrane demonstrated that APS is a promising technique for preparing macroporous inorganic membranes with the potential for cost-effective, energy-efficient and large-scale fabrication.

Manufacturing Process of Nanostructured Alumina Coatings by Suspension Plasma Spraying

This paper describes the formation process of nanostructured alumina coatings and the injection system obtained by suspension plasma spraying (SPS), an alternative to the atmospheric plasma spraying technique in which the material feedstock is a suspension of the nanopowder to be sprayed. The nanoscale alumina powders (d ≈ 20 nm) were dispersed in distilled water or ethanol and injected by a peristaltic pump into plasma under atmospheric conditions. Optical microscopy (OM), scanning electron microscopy (SEM), and x-ray diffraction (XRD) analyses were performed to study the microstructure of the nanostructured alumina coatings. The results showed that the nanoscale alumina powders in suspension were very easily adsorbed at the inner surface of injection, which caused the needle to jam. The rotation of the pump had a great effect on the suspension injection in the plasma. The very small resistance of the thin plasma boundary layer near the substrate can drastically decrease the impacting velocity of nanosize droplets. The concentration of suspension also has a significant influence on the distribution of the size of the droplet, the enthalpy needed for spraying suspension, and the roughness of the coating surface. The phase structures of alumina suspension coatings strongly depend on the plasma spraying distance. A significant nanostructured fine alumina coating was obtained in some areas when ethanol was used as a solvent. The microstructures of the coating were observed as a function of the solvent and the spraying parameters.

Investigation on Composite Coating of Low Grade Minerals

In this investigation, coatings of fly ash (an industrial waste) mixed with illmenite (a low grade ore mineral) have been deposited on mild steel and copper substrates using conventional atmospheric plasma spray technique. Micro-hardness measurement, phase composition analysis, coating porosity measurement, and surface and interface morphology are studied to characterize the coatings.

대기 플라즈마 용사공정을 이용한 Fe계 벌크 비정질 금속 코팅의 초기 분말의 화학조성과 크기에 대한 미세 조직 및 마모 특성

In this study, two kinds of Fe-based bulk metallic glasses (BMG) powder were built-up through atmospheric plasma spray (APS) technique. The microstructure of two coatings was analyzed through X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Crystallization and oxidation in coatings were affected by chemical composition and initial powder size. Then, both of them influenced the tribological property.

Plasma spheroidization and high temperature stability of lanthanum phosphate and its compatibility with molten uranium

Lanthanum phosphate has excellent thermal stability and corrosion resistance against many molten metals and other chemically corrosive environments. Lanthanum phosphate (LaPO 4 ) was synthesized from lanthanum oxalate by thermal dissociation of the oxalate to the oxide, followed by conversion to hydrated lanthanum phosphate (LaPO 4 ·0.5H 2 O). Thermal treatment of LaPO 4 ·0.5H 2 O above 773 K resulted in the irreversible transformation of the hydrated phase to the stable monazite phase. Thermal and chemical stability of monazite was studied by plasma spheroidization experiments using a DC thermal plasma reactor set up. Compatibility of monazite with molten uranium was studied by thermal analysis. Results showed that monazite is thermally stable up to its melting point and also is resistant towards attack by molten uranium. Adherent coatings of LaPO 4 could be deposited onto various substrates by atmospheric plasma spray technique.

Production and Characterization of Metastable ZrO2-Al2O3Coatings Obtained by APS + Quench

Producing nanostructured materials through metastable phases is an interesting novel route in the field of ceramic materials. Due to their small grain size and uniform structure, these nanostructured bulk materials exhibit very interesting properties. Metastable coatings can be produced starting from microstructured powders through atmospheric plasma spray technique, followed by a quenching route. The initial powders are melted during the spraying and deposited over a substrate that is quenched with liquid nitrogen feeders, producing metastable coatings. The thermal-sprayed coatings have been characterized using x-ray diffraction, scanning electron microscopy, field emission scanning electron microscopy, and energy dispersive spectroscopy. The properties of such coatings have been also studied obtaining promising results.

Production and Characterisation of Metastable Al<sub>2</sub>O<sub>3</sub>-TiO<sub>2</sub> Coatings Obtained by APS + Quench

It is well known that microstructure evolution during rapid solidification depends on the rate between undercooling and solidification velocity. Microstructural evolution in a nonequilibrium solidification process depends critically on the melt undercooling and growth (solidification) velocities of competing phases. One way of obtaining metastable structures is by Thermal Spray Technology. Metastable coatings can be produced starting from microstructured powders through Atmospheric Plasma Spray (APS) technique, followed by a quenching route. The initial powders are melted during the spraying and deposited over a substrate that is quenched with nitrogen feeders, producing metastable coatings. The obtained coatings were characterized using XRD, SEM, FESEM and TEM in the Thermal Spray Centre (CPT) of the University of Barcelona. The properties of such coatings were studied by hardness, obtaining promising results.

Production and characterization of metastable Al2O3–TiO2 ceramic materials

Producing nanostructured materials through metastable phases is interesting in the field of ceramic materials. Metastable phases can be obtained by the Atmospheric Plasma Spray (APS) technique which, is a well-known technique to produce coatings. The initial powders are melted during the spraying obtaining a homogenized phase due to their solubility in the liquid state. Afterwards, the molten droplets are quenched in a cooled medium, producing the sought metastable phases. Finally, during material consolidation, the metastable structure evolves due to a dual structure. A suppression of the grain growth is produced as a consequence of the immiscibility of both phases in the solid state. Due to their small grain size and uniform structure, these nanostructured materials exhibit very interesting properties such as higher hardness and toughness. The aim of this research has been to produce nanostructured Al2O3–TiO2 ceramic powders through APS + quenching route, starting from commercially available micron-sized powders. A complete characterization of the obtained structures using XRD, SEM, FESEM and EDS has been carried out in the Thermal Spray Center (CPT) of the University of Barcelona.