The aim of this paper is to compare the impact of plasma deposition processes onto Yttria Stabilized Zirconia (YSZ) electrolytes’ properties. Indeed, physical properties and microstructure of plasma sprayed coatings depend on the in-flight treatment of the particles in the plasma jet. Investigations of the relationships between spraying conditions and the in-flight properties of the particles upon impact for Air Plasma Spraying (APS) and Vacuum Plasma Spraying (VPS) were carried out using a MacLean & Anderson design of experiment. The In-flight particle properties were determined using the DPV 2000. For each type of plasma spraying process, coatings were elaborated with optimized plasma spraying conditions that allowed reaching the highest particle velocity upon impact keeping the highest temperature as possible. Coatings properties were then, evaluated by SEM and impedance spectroscopy.

Physical characteristics of Atmospheric Plasma Sprayed (APS) Alumina coating and Low Pressure Plasma Sprayed (VPS) Alumina coating were investigated. High purity Alumina powder was used for thermal spraying in this test. As electrical properties, the volume resistivity, dielectric constant, and the dielectric breakdown voltage were measured at R.T. to 873K. And the coefficient of thermal expansion, and the thermal conductivity were measured at also R.T. to 873K, as thermal properties. Mechanical properties, such as the Young’s modulus, the bending strength, and the cross-sectional hardness value were measured at R.T. As a test result, the Alumina coatings using both APS and VPS have similar properties except for the cross-sectional hardness value that was higher when sprayed by VPS.

This paper discusses a research project with the goal of homogenizing the properties of three-cathode plasma sprayed coatings through the use of advanced diagnostics and numerical simulations. The approach included the development of a suspension injection setup, the determination of plasma and suspension behavior through diagnostic methods such as computer tomography and particle image velocimetry, and the analysis of coating formation through computational fluid dynamics and finite element analysis. The results of their investigations are presented, including tomographic reconstructions of temperature distribution, suspension behavior measurements, and coating analysis. The paper concludes with a discussion of the future directions of their research and the potential impact on the field of thermal spray coatings.

Yttria doped zirconia has been widely employed as electrolyte materials for solid oxide fuel cells (SOFCs). Plasma spraying is a cost-effective process to deposit YSZ electrolyte. In this study, the 8 mol % Y 2 O 3 stabilized ZrO 2 (YSZ) layer was deposited by low pressure plasma spraying (LPPS) and atmospheric plasma spraying (APS) with fused-crushed and agglomerated powders to examine the effect of spray method and particle size on the electrical conductivity and gas permeability of YSZ coating. The microstructure of YSZ coating was characterized by scanning electron microscopy and X-ray diffraction analysis. The results showed that the gas permeability was significantly influenced by powder structure. The gas permeability of YSZ coating deposited by fused-crushed powder is one order lower in magnitude than that by agglomerated powder. Moreover, the gas permeability of YSZ deposited by LPPS is lower than that of APS YSZ. The electrical conductivity of the deposits through thickness direction was measured by potentiostat/galvanostat based on three-electrode assembly approach. The electrical conductivity of YSZ coating deposited by LPPS with fused-crushed powder of small particle size was 0.043 S × cm-1 at 1000°C, which is about 20% higher than that of APS YSZ with the same powder.

Tubular asymmetric LSCF oxygen transport membranes (OTMs) were prepared on stainless steel substrates by PS-PVD and supersonic air-gas plasma spraying (SAPS). The microstructure of the thermally sprayed OTMs is examined by cross-sectional imaging and oxygen permeability is assessed via oxygen permeation flux measurements carried out at atmospheric pressure in an air-helium gradient. The findings from the cross-sectional analysis and oxygen permeation tests are reported and discussed.

In this study, a TiO 2 (anatase) nanopowder suspension was processed by high velocity suspension flame spraying (HVSFS). The resulting coatings were characterized and compared to conventional HVOF and atmospheric plasma sprayed layers. It is shown that the HVSFS operating parameters can be adjusted to achieve dense titania with a near nanostructure and homogeneous distribution of anatase and rutile phases. These coatings have lower pore interconnectivity and higher wear resistance than the APS and HVOF layers. Alternatively, large unmelted agglomerates of anatase nanoparticles can be embedded in the coating, increasing the porosity and anatase content for enhanced photocatalytic efficiency.

Newly-developed multi electrode spraying systems have improved the process stability and coating properties in air plasma spraying (APS) significantly. The new generation three-cathode torches, i.e. TriplexProTM-200/210, can be operated without significant plasma fluctuations. In previous studies a numerical model, which couples fluid dynamic, electro-magnetic and thermal relationships to investigate the flow characteristics in the torch were introduced. In this study further development of the model with respect to meshing and turbulence model will be introduced. Furthermore, free jet simulations will be conducted which use temperature and pressure profile at the outlet of the torch as inletting boundary conditions. Advanced diagnostic methods will be implemented to verify the capability of the numerical models.

In this study, 316 stainless was deposited by low-pressure plasma spraying under various conditions to obtain different coating structures and by cold gas dynamic spraying for comparison. The coatings were characterized by cross-sectional metallography to assess porosity, oxidation, particle flattening, and elemental composition. The samples were also subjected to flyer plate impact testing in a gas gun to determine their shock propagation and porosity compaction properties. Comparing the results with that of the reference sample shows the effect of deposition conditions on the dynamic behavior of the coatings.

Thermal spraying of oxide ceramic suspensions containing fine and ultrafine powder particles is a new approach for manufacturing ceramic coatings exhibiting a refined microstructure. Suspension sprayed coatings clearly differ from conventionally sprayed coatings regarding microstructure phase composition and resulting mechanical properties. Several industrial applications may take advantage in future; among these are thermal barrier structures, thermal shock protection, solid electrolytes, catalytically active surfaces and wear resistant coatings. Two methods, namely Suspension Plasma Spraying (SPS) and High Velocity Suspension Flame Spraying (HVSFS) are suitable to process suspensions but lead to rather different coating structures due to differences in the achievable particle velocities and temperature. Generally, HVSFS can lead to more dense coatings with low porosity values. With SPS on the other hand, coatings with a high volume fraction of porosity featuring a homogeneous pore structure are achievable. The presentation will compare SPS and HVSFS regarding the spray process, achieved properties of the oxide coatings and potential applications.

In this study, MCrAlY-Al 2 O 3 composite powders were produced by ball milling and deposited by plasma, HVOF, and cold spraying. The results show that Al 2 O 3 fractions can be well controlled using composite powder due to non-preferential impact debonding of the matrix and Al 2 O 3 . The microstructure of spray powders is well retained in HVOF and cold-sprayed coatings due to the unmelted or partially molten condition of the spray particles. In the case of plasma-sprayed coatings, however, most Al 2 O 3 particles segregate at lamellar interfaces, forming a continuous oxide scale on the splat. The cold-spray coatings exhibit the highest hardness due to the work hardening effect of kinetic deposition.

In plasma spraying, H2 or N2 is commonly added to the primary Ar plasma which may increase the specific enthalpy, thermal conductivity and thus improve the process efficiency. The objective of this study is to provide a process characterization of a three-cathode plasma torch with various binary gas compositions. Several process diagnostics are used to characterize the impact of binary plasma gas mixtures in plasma spraying. High-speed video analysis is utilized to capture the jet fluctuations of the studied process parameters. In addition, current and voltage measurements are performed to further complement the plasma diagnostics. The impact of the binary plasma gas mixtures is determined using particle diagnostic system DPV-2000 by measuring the particle in-flight properties of Al 2 O 3 feedstock. Furthermore, the deposition efficiency (DE) of the investigated process parameters is determined. The results show that at the identical volumetric flow rate and current, the addition of H2 yields the highest particle temperatures, followed by Ar/N2 mixtures and pure Ar plasma. In reverse order, pure Ar plasma results in the highest particle velocities. In addition, the increased DE of plasma spraying with binary gas mixtures for Al 2 O 3 coatings offers the potential to increase the deposition rate of other ceramic materials. This study provides a comprehensive correlation between plasma and particle diagnostics and the deposition efficiency of binary plasma gas mixtures.

Despite the fact that plasma spraying has been a widely used technology over the past three decades, industries using this technology still need higher quality products. Presently, only a small degree of process control is used in most plasma spraying systems. Improved process control should lead to more consistent results and higher quality products. We discuss a relatively simple control scheme consisting of a microphone as a primary sensor and a fuzzy logic look-up model indicating the condition of the anode. Selected frequency peaks in the power spectrum of the microphone signal are analyzed online, and the results are correlated with an average jet length obtained from a series of high speed images. The jet length, in turn, is correlated with coating characteristics. A simple feedback control system is proposed which will counteract the negative effects of an eroded anode on coating quality.

This paper presents the results of a study of the morphology of alumina splats deposited on stainless steel and alumina substrates. The substrates were either plasma sprayed or coated via plasma enhanced CVD. Substrates that were plasma sprayed were annealed if necessary to get specific phase structures, then polished to around 0.4 μm (Ra). CVD-coated substrates with an Ra ~6 nm and a columnar amorphous structure were sprayed as deposited. Splat studies show that the crystal structure of alumina substrates and the release of entrapped gas have a major influence on splat formation. For plasma sprayed coatings, disk-shaped splats with excellent adhesion properties were obtained on hot γ alumina, while on α alumina, splat shape and morphology were irregular and adhesion very poor. The effect of entrapped gas, on the other hand, can be seen in the splats that formed on the CVD-coated substrates. These splats were very porous and, in many, most of alumina flowed out to rim. As the paper explains, this is the result of gas release upon impact of molten particles, which reduces wettability and thermal contact between the splat and substrate.

his paper examines the influence of nozzle bore diameter and plasma gas flow on the characteristics of plasma torch spraying. Large bore size allows high plasma gas flow rates to be achieved without an excessive increase in voltage, which is apt to damage the cathode. High flow rates (Ar: 1.3x10-3, H2: 1.3x10-4, He: 2.7x10-4 m3/s) are effective in imbuing more power into the plasma without the damage associated with higher chamber pressures. The relationships among key process parameters, including effective plasma power, electrical efficiency, chamber pressure, and plasma gas flow, are expressed qualitatively in the paper based on multiple regression analysis.

Polymeric substrates must be effectively cooled during plasma spraying to limit detrimental effects due to heat flow from the plasma jet. Even with the use of auxiliary cooling systems, however, some polymer substrates can undergo superficial modifications caused by particle heating at impact. This paper deals with chemical modifications in PET as a function of surrounding atmospheres during plasma processing. It also explains how aluminum coating adhesion was determined using tensile tests.

The aim of this work is to better understand the build-up of thermal barrier coatings (TBC) on microtextured substrates, particularly the influence of geometry on the behavior of plasma jets in substrate boundary layers. Coatings produced by suspension plasma spraying served as an experimental reference for numerical analysis, which involved advanced turbulent flow and volumetric heat source modeling along with the use of commercial fluid flow software. Geometric and numerical models were used to simulate the generation of plasma inside the torch and the resulting plasma flow with its highly nonlinear thermophysical characteristics. This work opens the possibility of predicting feedstock particle movement and deposition, which is essential in understanding coating build-up mechanisms in general and the flow of fine particles on substrate surfaces in particular.

Mathematical and computer models of movement and heating of particles in low pressure conditions are developed. The mathematical models are based on the molecular-kinetics theory of gases. A program complex for computer realization of models is developed. It contains a built-in data base of temperature dependent properties of substances, system of processing and graphic visualization of simulation results. For verification of the developed models, computer simulation and experimental measurements of Al2O3 particle temperature and velocity are conducted. These materials were sprayed with Plasma-Technik equipment at pressure 60 mBar in argon. Particle velocity was measured with a special optical device, particle temperature was defined by intensity radiation method. It was established that the developed models are adequate to real process (error of 5-8 %) and may be used for study and improvement of VPS processes.

The present study is conducted to simulate the multi-component chemical reactions of a turbulent argon-hydrogen plasma jet flowing into the surrounding atmosphere under typical operating conditions. Based on the initial spraying process parameters, the temperature, velocity profiles and the basic chemical species at the nozzle exit are calculated, and then used for the boundary conditions of the next step, where the chemical reactions in the multicomponent plasma jet are calculated by employing the Eddy-Dissipation model and the Realizable k-ε turbulence model. As the result of the calculation, the distribution of the mole fractions of the products as well as the temperature and velocity distributions is discussed. The approach presented in this paper will be theoretically helpful to perform further analysis of the interaction between the plasma and the particles.

The heat and momentum transfer of the plasma to the injected particles is an important issue in coating formation during plasma spraying. In this study, the plasma temperature and velocity of a Triplex-I torch was measured by means of an enthalpy probe system. Additionally, the properties of injected yttria-stabilized-zirconia powder of a fine sized fraction were recorded spatially resolved by using a DPV2000 system. The plasma temperature and velocity are decreasing by increasing the distance from 45 to 60 mm with respect to the torch exit by approximately 50% from initially 6200°C and 400 m/s, respectively. In contrast, the particles gain temperature up to the melting point at 70 mm stand-off distance as well as the velocity rises up to its highest value of 115 m/s at the maximum flow rate of the particles. Both, plasma and particle characteristics were used to obtain a deeper insight on heat- and momentum transfer of the plasma jet to the single particles.

The temperature of in-flight particles in plasma spraying is one of the main parameters affecting the coating microstructure. Temperature measurement has been carried out before for inflight particles in air plasma spray (APS) and other thermal spraying processes. Suspension plasma spray (SPS) is an emerging coating deposition technology that permits the deposition of nanostructured coatings with unique structural characteristics. The aim of this work is to evaluate the influence of radiation emitted by the plasma and metallic vapors on temperature measurement of SPS particles performed by two-color pyrometry. To do so, spectroscopic analysis in the visible to near-infrared range is carried out on the jet stream when suspension of 20wt% YSZ particles in ethanol is sprayed. The analysis takes into account the radiation scattered by the particles (Mie scattering) as well as the radiation directly detected from the jet stream, and it was found that the effect of the scattered radiation by the particles on temperature measurement is 1 degree at its melting point (2700°C) and 16 degrees at 2500°C.