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1-16 of 16
Poster Session: Plasma Spraying and Plasma Transferred Wire Arc Processes
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Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 1372-1374, June 2–4, 2008,
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An amorphous Yttria Stabilized Zirconia (YSZ) ceramic powder feedstock is successfully used to produce a novel YSZ ceramic coating by plasma spraying process, in this paper. Unlike conventional atmosphere plasma spray (APS) and solution precursor plasma spray (SPPS) YSZ coatings, the YSZ ceramic coating fabricated by plasma spraying amorphous YSZ ceramic powder feedstock reveals complex structure of cell and ultrafine particles instead of conventional splats and porous structure. A large number of ultrafine particles are found in the cell. Phase structure of the YSZ ceramic coating is tetragonal. Porosity is about 31%. In addition, thermal cycling test is nearly 370 cycles, and the thermal conductivity is 1.0 W.m-1.K-1, at 1250 temperature. Based on these excellent properties, the YSZ ceramic coating fabricated by plasma spraying amorphous YSZ ceramic powder feedstock should be used as high-temperature abradable sealing coatings and thermal barrier coatings (TBCs).
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 1375-1380, June 2–4, 2008,
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Invar alloy (Fe – 36%Ni) is used in industrial applications which require high dimensional stability because of its exceptionally low thermal expansion coefficient. Purpose of this work is to enhance the performance of molds for the production of carbon fiber reinforced plastic (CFRP) components. Four different kinds of commercial powders were coated on an Invar substrate: Al 2 O 3 - 12TiO 2 , Cr 2 O 3 and ZrO 2 - 8Y 2 O 3 by Air Plasma Spray (APS) and WC - CoCr by High Velocity Oxygen Fuel (HVOF). Metallographic microscopy observation and SEM analysis were carried out and microhardness and fracture toughness were evaluated by means of the micro - indentation method. Friction behaviour and wear resistance were evaluated in dry sliding conditions with Pin On Disk apparatus for not coated Invar substrate and for the different coated substrates. Chromium oxide and tungsten carbide coatings exhibited higher mechanical characteristics respect to the other coatings: chromium oxide had the higher hardness value and tungsten carbide the higher fracture toughness. Tungsten carbide coating had the lower average coefficient of friction and together the chromium oxide the lower wear mass loss and wear rate. Among APS ceramic coatings, Cr 2 O 3 exhibited the best mechanical and tribological behavior while the HVOF cermet coating exhibited the best behavior among all the coatings.
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 1381-1384, June 2–4, 2008,
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The jet characteristics of supersonic plasma jet spraying (SPJS) system were studied. Comparison of jet property was made between conventional plasma spray system and SPJS system. The results showed that the characteristics of the SPJS system are superior to the latter system. The particles velocities in the range of 400~800 m/s are obtained for supersonic plasma jet guns with 4.5 mm diameter nozzles and 60 l /min total gas flow rates, SPJS operate about 36 KW. The particle velocity is more than two times as much as conventional plasma jet spraying. The supersonic plasma jet is much longer than that of the conventional torch. It can bring about improvement for flying powder heated and accelerated and also prolong spray distance.
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 1385-1386, June 2–4, 2008,
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Strontium aluminates activated by Eu, Dy 3+ ions has recently attracted more attention due to not only their bright luminescence and super long afterglow without radioactivity but also the extensive application. SrAl 2 O 4 :Eu, Dy coatings were prepared by low power plasma thermal spraying (2.5-4W). The optimum spraying conditions have been established with spray parameters. The effects of the plasma conditions on the porosity rate of the coatings were investigated by many techniques, respectively X-ray diffraction (XRD) and scanning electron microscopy (SEM). To better qualify the characteristics of these coatings prepared from spray-dried powders, luminescence characteristics were also studied.
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 1387-1392, June 2–4, 2008,
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In plasma spray process, ceramic coatings can be sprayed by using either argon-hydrogen or nitrogen-hydrogen plasma gas mixtures. Starting from a given particle size distribution the question is what are the spray parameters allowing achieving similar coatings with these types of plasmas? The problem is made more complex because a torch working with Ar-H 2 is different from that using N 2 -H 2 as plasma forming gas. It is thus necessary to compare the gas mixture properties, the torches working conditions (mean voltage and thermal efficiency for given current), the arc column diameter relatively to the nozzle internal diameter and the spray parameters, the arc root fluctuations, the powder injection, the particles mean temperatures and velocities as well as their fluctuations linked to those of arc root, the splat formation, the coating porosity and deposition efficiency. This comparison has been achieved for ZrO 2 -Y 2 O 3 (7 vol%) powder with a size distribution between 5 and 25 µm and using the same plasma torch for the two plasma gas mixtures: a 3MB torch with a cylindrical anode nozzle and 5.5 mm in internal diameter.
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 1393-1399, June 2–4, 2008,
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Increasing erosion of the anode wall of a single-cathode F4 torch changes the fluctuation pattern of the plasma jet. Trajectories and temperature history of particles injected into the plasma become accordingly modified. In this work such fluctuations are characterised through spectral analysis of the torch voltage as well as of the light intensity of the jet outside the torch. Instead of considering the evolution of the main peaks in the frequency spectrum for both voltage and optical signals, the variation with increasing torch wear of the spectrum’s higher frequency fraction (above 20kHz) is focused on. The evolution of the fractal dimension in this high frequency range exhibits a reliable correlation with the erosion of the anode wall. This is confirmed further by the development of a simple stochastic model for the motion of the arc root along the anode wall. This model yields, depending on the probability for a pronounced arc root jump, a fractal dimension and an evolution just within the range observed in the measurements. Additionally, tracking the fluctuations at different locations outside the torch enables the isolation of the fluctuation dissipation due to jet viscosity and velocity.
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 1400-1405, June 2–4, 2008,
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Tungsten-copper composites and FGMs can find applications in various thermal management systems. One example is plasma facing components for nuclear fusion devices, where tungsten provides the heat-resistant plasma facing armor, copper provides the highly conductive heat sink, while the composite or FGM can reduce the stress concentration at the interface. In this study, W+Cu composites of various compositions were produced by water-stabilized plasma spraying. With the help of in-flight particle and plume diagnostics, the powder injection was optimized for each material, and the feed rates were adjusted to account for different deposition efficiencies. The composition, structure, thermal and mechanical properties of the coatings were characterized.
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 1406-1410, June 2–4, 2008,
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During plasma spraying, high substrate temperature contributes to increase the interface temperature between flattening droplet and substrate and subsequently promotes the through-lamella grain growth in the coating. In this study, yttria stabilized zirconia (YSZ) coatings are prepared by atmospheric plasma spray (APS) on the stainless steel substrate preheated to different temperatures from room temperature to 1100°C. The microstructure of the coatings is characterized from polished and fractured cross sections by SEM. The ionic conductivities of the coatings are measured using both DC and AC methods, and the relationship between ionic conductivity and microstructure of coatings is examined. SEM observation shows that the coatings exhibit different microstructures with different substrate temperatures. With the increase of substrate temperature, the columnar grain growth continuously across lamellar interfaces is enhanced and subsequently the intersplat bonding ratio in the coating is increased. The ionic conductivity of YSZ coatings at the direction perpendicular to coating surface is significantly increased through the microstructure development by increasing deposition temperature.
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 1411-1416, June 2–4, 2008,
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Yttria stabilized zirconia (YSZ) splats were plasma sprayed on the YSZ substrate preheated to different temperature to examine the influence of the temperature of the underlying surface on which molten droplet impacts on deposition characteristics. The splat morphology and the bonding at the splat-substrate interfaces were examined by SEM. It was found that the crack density decreases rapidly with the increase of the temperature when the splat were formed on an YSZ substrate preheated to above 800°C. The nucleation of YSZ melt on the base of YSZ substrate grains takes place during solidification leading to the formation of the bonding between the splat and substrate when the temperature is increased to over 600°C. The substantial bonding was observed at the interface between YSZ splat and YSZ substrate as the temperature is increased to over 800°C. The results revealed that the temperature of the previous splat on which a molten droplet impacts significantly influence the formation of the interface bonding. In addition, the mechanism and condition for the bonding formation of a splat on a substrate with the identical compositions were discussed.
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 1417-1423, June 2–4, 2008,
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Parametric drifts and fluctuations occur during plasma spraying. These drifts and fluctuations originate primarily from electrode wear and intrinsic plasma jet instabilities. One challenge is to control the manufacturing process by identifying the parameter interdependencies, correlations and individual effects on the in-flight particle characteristics. Such control is needed through methods that (i) consider the interdependencies that influence process variability and that also (ii) quantify the processing parameter-process response relationships. Artificial intelligence is proposed for thermal spray applications. The specific case of predicting plasma power parameters to manufacture grey alumina (Al 2 O 3 -TiO 2 , 13% by wt.) coatings was considered and the influence of the plasma spray process on the in-flight particle characteristics was investigated.
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 1424-1428, June 2–4, 2008,
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Thermal barrier coatings (TBCs) were deposited by an Air Plasma Spraying (APS) technique. The coating comprised of YSZ – 0, 20, 50 and 80 wt % Al 2 O 3 ; NiCrAlY bond coat; and AISI 304L stainless steels substrate. Thermal shock tests were performed over the specimens, at 1000 °C and 1200 °C for 5 min and then forced air quenching. The samples were directly pushed into a tube furnace at 1000 °C and 1200 °C. The results were prominent in forced air quenching tests at 1000 °C , where the lives of the TBCs were observed more than 66 cycles. It was noticed that with increase of Al 2 O 3 content the thermal shock life of the specimens decreased. Further, the coating roughness decreased by Al 2 O 3 addition. It was observed that with decrease in coating roughness, the thermal shock life decreased slightly.
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 1429-1432, June 2–4, 2008,
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Lanthanum silicate coatings were deposited onto stainless steel substrates by atmospheric plasma spraying (APS) using mechanically mixed (type A) and calcined feedstock (type B) powders. The phase composition, microstructure, density and porosity of coatings prepared from the two types of powder were compared.
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 1433-1438, June 2–4, 2008,
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A simple and efficient numerical model describing the processes of nucleation, growth, and transport of multicomponent nanoparticles is developed. The approach is similar to the classical method of moments but can be applied to co-condensation of several substances. The processes of homogeneous nucleation, heterogeneous growth, and coagulations due to Brownian collisions are considered in combination with the convective and diffusive transport of particles and reacting gases within multidimensional geometries. The model is applied to the analysis of multi-component co-condensation of TaC nanoparticles within a DC plasma reactor.
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 1439-1444, June 2–4, 2008,
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From the past studies of the residual stress occurred during the plasma spraying, the different results were obtained; the arguments of these previous works were not only in the value of residual stress but the stress state existed in the HACs. The residual stress generation theory stated in these literatures appear to be oversimplified, hence a more basic study is needed to explore the contention on the residual stress state in HA coating during plasma spraying. In this study, in order to obtain the whole and accurate residual stress value and state, the residual stress was measured by using the material removal method. For the purpose of inferring the generation mechanism of residual stress, the particular forms of the substrate holder and various cooling system were employed. The results show that the difference between the HAC and substrate temperature is the main factor that dominates the residual stress state. HAC/Ti-substrate on the hollow rotational holder with the back cooling system would lead to the higher temperature in coating than substrate during plasma spraying and result in the tensile residual stress in the HAC. On the contrary, HAC with the front cooling system displayed much lower temperature than the Ti-substrate that fixed on non-hollow holder and hence the compressive residual stress occurred. These could be attributed to the differences of volume shrinkage between the HAC and Ti-substrate that from different initial temperature to room temperature. In another word, the residual stress state is depended on the spraying program not always tensile or compressive state.
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 1445-1449, June 2–4, 2008,
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The present paper examines a hybrid DC arc thermal plasma torch with gas-water stabilisation and its application for thermal spraying. The torch was worked out based on the water-stabilised plasma torch WSP, main features of which are high temperature of the generated plasma and high powder through-put. In the hybrid torch the cathode part is modified in the way like in gas torches, which not only provides proper stabilisation of the arc in this region and cathode protection from contact with stabilising water but also allows to vary properties of the generated plasma. Change of the secondary gas flow rate, which is usually argon, results in strong changes of the plasma gas density, while the energy balance of the torch remains almost unchanged. This in turn leads to modification of the plasma jet properties. The paper describes effect of the plasma torch parameters on behaviour of the generated plasma jet and injected powder particles. The results show how particle velocities follow changes of the plasma jet properties according to the plasma torch operation parameters. Both increase of arc current and argon flow rate provided increase of particle velocities.
Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 1450-1452, June 2–4, 2008,
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Abstract-Solution precursor plasma spray (SPPS) is a relatively new thermal spray process in which chemical precursors are injected into DC-arc plasma spray torch in place of powder. This process is able to make relatively porous (15-25% porosity) thermal barrier coatings with through-thickness cracks that enhance their thermal strain resistance. The SPPS process can also make dense titania and alumina zirconia coatings. The process can make thin and thick coatings, dense and porous coatings, structural and functional preforms, new compositions, and metastable materials. Metastable materials arise because the solution is molecularly mixed and the cooling rate in thermal spray is high. The process has the disadvantage of needing to provide energy to evaporate the solvent and of being a new process where less extensive empirical knowledge and modeling insights exist, compared to air plasma spray with powders. The microstructure process parameter relation is explored. Results from modeling studies concerning evaporation of droplets and related solute concentration gradients, modeling studies of aerodynamic break-up and experimental studies of non-aero-based droplet break-up and of the effects of solution concentration will be described. These studies will be related to experimental results for making dense coatings.