Search Results for atmospheric plasma spraying

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.

The commonly used method for preparing EBCs is atmospheric plasma spraying (APS), but it has problems such as easy oxidation of the coating, low spraying power, and low substrate temperature, resulting in the coating having multiple pores, cracks, and insufficient density. The new plasma spraying physical vapor deposition (PS-PVD) technology can solve these problems. This article compares the microstructure, mechanical properties, and phase composition of EBCs prepared using APS and PS-PVD processes.

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.

We present the results of an investigation of the effects of a travelling magnetic field (TMF) on the plasma flow using a commercial program package. The argon plasma generation in the electric arc and the Lorentz force induced by the TMF are simulated with specific equations, which are derived from the magnetofluiddynamic equations using appropriate simplifications. First calculations confirm the predicted effects.

Samaria-doped ceria (SDC) has become a promising material for the fabrication of intermediate-temperature, metal-supported solid oxide fuel cells (SOFCs). While typical SOFC materials, such as yttria-stabilized zirconia (YSZ), require high temperatures (> 700°C) to exhibit suitable ionic conductivity for high cell performance, SDC displays similar ionic conductivities at lower temperatures (600°C – 650°C). The atmospheric plasma spray (APS) process is a promising technique for manufacturing metal-supported SOFCs. In this study, the in-flight characteristics, such as particle velocity and surface temperature, of spray-dried SDC agglomerates were analyzed at various plasma spray conditions using the DPV-2000 in-flight particle sensor manufactured by Tecnar Automation. Coatings of SDC were applied on stainless steel substrates using a range of spray conditions, and their resulting microstructures and deposition efficiencies were analyzed. It was found that particle temperature could be related to the specific plasma energy, and that coating porosity was related closely to the measured average particle temperature.

This study investigates the influence of plasma gas composition on deposition efficiency achieved during atmospheric plasma spraying and the properties of the resulting deposits. In the experiments, ternary mixtures of argon, hydrogen, and helium are used in different combinations and flow rates to spray Al 2 O 3 -TiO 2 and ZrO 2 -Y 2 O 3 powders on test substrates while measuring deposition efficiency. Several coating properties are measured, including porosity, hardness, and bond strength, and correlated with plasma gas ratios. Paper text in German.

Understanding the particle injection into the gas flow issuing from an APS torch is necessary to optimize the spraying parameters. In order to solve numerically this task, the distribution of gas velocity and temperature at the torch outlet is required. In this work this is achieved by developing a model which not only delivers the solution for the electrically charged gas flow within the torch, but also includes the thermodynamical condition of minimum entropy production. This additional condition fixes the size of the electric arc inside the torch, whose radius is particularly responsible for the form of the calculated velocity and temperature profiles at the torch nozzle. The velocity and viscosity of the gas flow near the torch outlet mainly control the trajectory of particles injected into the gas flow. For the typical gas mass flow and torch power used in APS, the resulting temperatures at the gas core are slightly above the ionization temperature of the gas species. The radial location of the viscosity maximum corresponding to the ionization temperature is calculated, since this maximum strongly influences the particle trajectory. Finally, the influence of plasma fluctuations on the heat transfer to the injected particles is discussed.

This work examines the corrosion behavior of cobalt and nickel base coatings produced by APS and HVOF spraying. Laser fusing and sealing are also assessed for comparison as are the corrosion properties of tungsten carbide, chromium carbide, and chromium oxide. All coatings and processes are analyzed by cyclic polarization testing and optical and scanning electron microscopy. Test results are presented and discussed along with the relative merits of each process.

Atmospheric plasma spray parameters were developed for a three-cathode torch with a high-velocity nozzle and MCrAlY powders of different particle size fractions. The main objectives of the work are to achieve bond coats with low oxygen content and porosity. Other goals are achieving sufficient surface roughness at high deposition rates and efficiencies. The oxidation behavior of the sprayed coatings was characterized by thermal gravimetric analyses and isothermal heat treatments.

The emergence of lanthanum silicate as an electrolyte is required to accelerate the development of synthesis techniques for intermediate temperature solid oxide fuel cells (ITSOFCs). Apatite-type oxide powders of La 10 (SiO 4 ) 6 O 3 have been elaborated through atmospheric plasma spraying (APS) using micro-scale mixtures of La 2 O 3 and SiO 2 powders. Granulometer and scanning electron microscopy analyses have indicated the result of high temperature reaction and rapid solidification in the evolution of multi-scale microstructure.

Environmental barrier coatings (EBCs) are required to protect SiC based composites in high temperature, steam containing combustion environments found in the latest generation of high efficiency gas turbine aeroengines. Ytterbium disilicate has shown promise as an environmental barrier coating, showing excellent phase stability at high temperature and a coefficient of thermal expansion close to that of SiC; however, its performance is dependent on the conditions under which the coating was deposited. In this work, a parametric study was undertaken to demonstrate how processing parameters using a widely used Praxair SG-100 atmospheric plasma spraying torch affect the phase composition, microstructure and mechanical properties of ytterbium disilicate environmental barrier coatings. Ytterbium disilicate coatings were deposited using 5 sets of spray parameters, varying arc current and secondary gas flow. The phases present in these coatings were quantified using X-ray diffraction with Rietveld refinement, and the level of porosity was measured. Using this data, the relationship between processing parameters and phase composition and microstructure was examined. Abradable coatings are used throughout gas turbine engines to increase efficiency in the compression and combustion phases of the turbine. Abradable coatings are soft enough to be worn away by turbine blade tips (without damaging the tip itself), allowing for tighter clearances to be used, limiting leakages and increasing efficiency. Using the optimum process parameter window determined in this work, a low density abradable Yb 2 Si 2 O 7 layer will be deposited in future research.

In-flight particle state has been shown to play a crucial role in determining the properties of thermally sprayed coatings. Therefore, process control strategies have been suggested to keep the in-flight particle state constant in order to decrease the variability of coating quality. Such strategies are already used to some extent in industrial applications, where the particle state is measured before starting the coating of a part to make a go/no-go decision based on whether the values are inside a predefined process window. This paper shows the importance of the evaluation procedure of the in-flight particle state, with focus on process control applications. The paper demonstrates this on the example of atmospheric plasma spraying (APS) of yttria-stabilized zirconia (YSZ), using a commercially available sensor system Accuraspray for measuring the ensemble particle temperatures and velocities as descriptors of the in-flight particle state. It is concluded that the stabilization time of the particle jet might be different from what is practically considered. Moreover, the paper investigates an approach of monitoring the in-flight particle state during a coating run without having to install the sensor system on the robot arm.

The potential of atmospheric plasma spraying (APS) technology has been investigated for the manufacture of anode, electrolyte and cathode of a solid oxide fuel cell. As substrates tape-casted or commercial available porous plates both made of a FeCr-alloy were used. The functional layers were applied by atmospheric plasma spraying, however, it turned out that screen printed LSCF cathodes performed better than thermally sprayed versions. Anode layers with high electrochemical activity could be produced by APS using separate injections of NiO and YSZ powders. The manufacturing of gas-tight electrolyte layers was a key-issue of the present development. With adequate processing conditions and advanced gun technology it was possible to produce highly dense ceramic coatings with a very low amount of micro-cracks and pores. These electrolytes gave high open cell voltages above 1 V corresponding to the low measured leakage rates (<10-3 mbar*l/s) of the rather thin (<50 µm) coatings. Additional layers have been applied to reduce the interdiffusion especially of species from the metallic substrates into the anode. These layers could significantly reduce degradation of the cells. SOFCs with a power density at 800°C well above 0.7 W/cm² could be produced by the developed technology.

The disadvantage of plasma torches using conventional single cathode techniques is the occurrence of azimuthal and axial instabilities inside the plasma torch. This causes electrical power fluctuations which result in inhomogeneities of the plasma jet enthalpy and with that an uneven plasma particle interaction. Hence, variations in particle properties occur and consequently an uneven coating quality is produced. Using the triple-cathode technique these electrical power fluctuations were successfully reduced, resulting in a stationary plasma flow. Thus this technique appears to offer the potential to homogenize coating properties. Similar results have been shown for plasma torches with triple anode arrangements. The goal of this research group is to homogenize properties of plasma sprayed coatings using of 3-cathode and 3-anode technologies based on numerical simulations. The approach used is to subdivide the complete APS process into the areas plasma torch, free jet as well as coating formation and characteristics. By simulation of the individual areas and combination with experimental results the corresponding process parameters will be obtained for the desired coating properties.

In this work numerical simulation results of the impact and solidification of molten PYSZ-particles on flat and rough substrate surfaces are presented. This investigation deals with the effect of the particle state prior impact, particle diameter and substrate roughness, on splats spreading behaviour and final morphology. The particles have a diameter range between 20 – 60 µm. Particle initial conditions prior to impact: speed, temperature and melting state, are taken from previous simulation modelling approaches of particle accelerating and heating. Simulations of fluid dynamics, heat transfer and solidification during the particle impact were performed using computational fluid dynamics. Tracing of free surfaces determinates volume of fluid method. Heat flux at the particle-substrate interface and temperature dependent liquid phase viscosity of PYSZ are studied and discussed. Simulated splat morphologies are compared with experimentally obtained splats.

Lanthanum zirconate (La 2 Zr 2 O 7 ) was proposed as a promising material for thermal barrier coatings. At atmospheric plasma spraying (APS) of La 2 Zr 2 O 7 a considerable amount of La 2 O 3 can evaporate in the plasma flame, resulting in a non-stoichiometric coating. As indicated in the phase diagram of the La 2 O 3 -ZrO 2 system, in the composition range of pyrochlore structure, the stoichiometric La 2 Zr 2 O 7 has the highest melting point and other compositions are eutectic. APS experiments were performed with a TriplexPro-200 plasma torch at different power levels to achieve different degrees of evaporation and thus stoichiometry. For comparison, some investigations on Gd 2 Zr 2 O 7 were included which is less prone to evaporation and formation of non-stoichiometry. Particle temperature distributions were measured by the DPV-2000 diagnostic system. In these distributions, characteristic peaks were detected at specific torch input powers indicating evaporation and solidification processes. Based on this, process parameters can be defined to provide stoichiometric coatings intended to show good thermal cycling performance.

The goal of this research group is to homogenize properties of three-cathode plasma sprayed coatings on basis of numerical simulations and advanced diagnostics. Results of the first project phase as well as an outlook to future work are presented. A numerical model for investigation of plasma flow in the free jet, produced by three-cathode torch was developed. Modelling results are verified by plasma diagnostics (Computer Tomography). In order to include particle shrinking effects, coating formation simulation is accomplished by a newly developed model, based on Computational Fluid Dynamics coupled with the Finite Element method, whereat diagnostics carried out in the fields of particle diagnostics. During the next phase of the project, the investigation of the plasma free jet and particle injection by advanced diagnostics and simulation respectively is scheduled. In a subsequent stage the transition from conventional particles to suspensions will be considered. Coating formation simulations are scaled up to dimensions of macroscopic tensile tests. By combining these overarching investigations, appropriate process parameters for homogenized coatings will be obtained.

Yttria-stabilised zirconia (YSZ) coatings were deposited on austenitic stainless steel coupons from nanostructured powders using atmospheric plasma spraying (APS). Two suspensions of YSZ nanoparticles were used as starting material: a diluted commercial suspension and a highly concentrated in-house prepared suspension (obtained by adding an YSZ submicronic powder to the diluted suspension). Both suspensions were reconstituted into sprayable micrometric granules. The reconstitution process was performed by spray drying, followed by a thermal treatment in order to reduce porosity and enhance agglomerate sinterability. The reconstituted powders were characterised by XRD, SEM, granule and pore sizing techniques, and a flowability evaluation. The effect of suspension characteristics on granule morphology and porosity was examined. The reconstituted powders were successfully deposited, yielding well-bonded coatings. The coating microstructure was characterised by XRD and SEM. Mechanical properties and erosion resistance were also determined. Coating microstructure consisted of semi-molten feedstock agglomerates surrounded by fully molten areas that acted as binders. The influence of feed powder characteristics on coating microstructure and properties was also studied.