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T. Inoue
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Proceedings Papers
ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 495-499, June 2–4, 2008,
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SrTiO x is an expected oxide thermoelectric material, which performance can be improved by doping Y 3+ in place of Sr 2+ . However, the maximum content of Y 3+ is limited to about 10% because of the phase transformation in the equilibrium sintered material. By contrast, plasma sprayed (Sr, Y)TiO x , which was essentially rapidly quenched, could solve Y up to 20% of Sr-site without the second phase, and produce the increase in the electric conductivity and the decrease in the thermal conductivity. But the absolute value of Seebeck coefficient decreased with an increase of Y content. As the result, the ZT value, which showed the performance for thermoelectric power generation, was reached only 0.1 in the Y content range 10% to 25% of Sr site.
Proceedings Papers
ITSC 2007, Thermal Spray 2007: Proceedings from the International Thermal Spray Conference, 313-318, May 14–16, 2007,
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A thermoelectric power generating device, in which all components were fabricated by plasma spray technique, was manufactured and its performance was evaluated. Its basic unit was composed of (Ca,Bi) 3 Co 4 O 9 p-type semiconductor chip and (Sr,Y)TiO 3-x n-type semiconductor chip. The plasma sprayed (Ca,Bi) 3 Co 4 O 9 and (Sr,Y)TiO 3-x deposits showed the Seebeck effect according to expectation. However, the ZT values, which indicated the thermoelectric performance, were still poor because of the low electric conductivity. Measurements of some basic properties revealed that increase of the target phase content was important for the p-type material. On the other hand, decrease of the resistivity was strongly desired for the n-type material by process improvement. Power generating test was performed using pipe shape device fully fabricated by plasma spraying and the electric output was successfully obtained under a temperature gradient.
Proceedings Papers
ITSC 2007, Thermal Spray 2007: Proceedings from the International Thermal Spray Conference, 523-527, May 14–16, 2007,
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Studies on plasma spraying of zircon (ZrSiO 4 ) have been carried out by the authors as one of the candidates for an environmental barrier coating (EBC) application, and had reported that substrate temperature is one of the most important factors to obtain crack-free and highly-adhesive coating. In this study, several amount of yttria were added to zircon powder, and the effect of the yttria addition on the structure and properties of the coatings were evaluated in order to improve the stability of the zircon coating structure at elevated temperature. The coatings obtained were composed of yttria stabilized zirconia (YSZ), glassy silica, while the one prepared from monolithic zircon powder composed of the metastable high temperature tetragonal phase of zirconia and glassy silica. After the heat treatment over 1473K, silica and zirconia formed zircon in all the coatings. However, the coatings with the higher amount of yttria had less amount of zircon formed. This resulted in the less open porosity of the coating at elevated temperature. These yttria added coatings also showed good adhesion even after the heat treatment, while monolithic zircon coating had peeled off.
Proceedings Papers
ITSC 2006, Thermal Spray 2006: Proceedings from the International Thermal Spray Conference, 763-768, May 15–18, 2006,
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Alumina-zirconia nano-composite coating were fabricated by plasma spraying using agglomerated feedstock from alumina and yttria partially stabilized zirconia fine powders of about 100 nm in diameter. The coating was very dense and showed the striped contrast in the splats. XRD analysis and TEM observation revealed that the splats contained gamma-alumina and tetragonal-zirconia crystals, which sizes were under 10 nm. The striped contrast in the splats corresponded to the inhomogeneous distributions of these crystals. To investigate the mechanical properties of this nano-composite coating, micro-hardness and fracture toughness were measured. The critical strain energy release rate of nano-composite coating was 106.4 J/m 2 , which was two times larger than YSZ coating.
Proceedings Papers
ITSC 2004, Thermal Spray 2004: Proceedings from the International Thermal Spray Conference, 138-142, May 10–12, 2004,
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A new method for evaluating the tensile adhesive strength of thermal sprayed coatings has been developed using a test specimen that incorporates an artificially introduced circumferential crack to control the stress intensity factor at the crack tip along the interface between the coating and the substrate. FEM-analysis is carried out to calculate a correction factor and the stress intensity factor for the test specimen. When the results of tensile test are sorted out using the stress intensity factor at which failure occurred, constant values should be obtained regardless of changes in geometry such as crack length and the diameter of test specimen. The method was first applied to air plasma spray (APS) coatings and then to HVOF sprayed coatings. Effects of substrate preparation such as surface roughness and preheating temperature on the resultant coating adhesion were studied experimentally.
Proceedings Papers
ITSC 2004, Thermal Spray 2004: Proceedings from the International Thermal Spray Conference, 831-836, May 10–12, 2004,
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Alumina-zirconia composite coatings were fabricated by plasma spraying using both of mixture of commercial feedstocks and agglomerated feedstock from fine powders of about 100 nm. The coating from mixture had an ordinary lamella structure which consisted of alumina splats and zirconia splats, whereas that from fine powders showed the striped contrast in the splat. X-ray deflection profiles revealed that the latter contained gamma-alumina, monoclinic-zirconia and tetragonal-zirconia crystals, which sizes were under 10 nm. These facts mean the fine crystals dispersed inhomogeneously. The nano-composite coating had a higher Vickers hardness and lower thermal diffusivity than the coating from mixture. Moreover, it showed good thermal stability and its crystallite size kept under 50 nm even after the heat treatment at 1500°C for 100h.
Proceedings Papers
ITSC 2004, Thermal Spray 2004: Proceedings from the International Thermal Spray Conference, 852-856, May 10–12, 2004,
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Nano-dispersed α-Al 2 O 3 /YAG composite coatings were successfully obtained by plasma spraying of the granulated Al 2 O 3 /Y 2 O 3 powder, and the post heat treatment. The as-sprayed coating was composed of an amorphous phase, metastable Y-Al-O solid solution. After the heat treatment around 1473K, two crystalline phases, α-Al 2 O 3 and YAG, precipitated, so that the fine dispersed Al 2 O 3 /YAG composite coatings were formed. The sizes of the precipitates could be widely controlled by time and temperature of the heat treatment. Hardness and wear property were evaluated in this nano-structured CMC coating.
Proceedings Papers
ITSC 2003, Thermal Spray 2003: Proceedings from the International Thermal Spray Conference, 597-601, May 5–8, 2003,
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The effect of the chamber pressure and the spray distance on the splat formation of the plasma sprayed spherical alumina powder was investigated. The velocity and the surface temperature of the sprayed particles were measured by DPV2000. The particle temperature was changed in wide range by the chamber pressure; a solid core remained in the sprayed particle at 30 kPa and the surface temperature reached to the boiling point of alumina over 90 kPa. At the higher temperature, the splashing behavior was explained by the model of liquid film stability. However, in the cooling stage after coming out from the plasma flame, the inhomogeneous temperature in the sprayed alumina particle led to the complex splashing. The temperature distribution in the molten particle is very important to consider the splat formation.
Proceedings Papers
ITSC 2003, Thermal Spray 2003: Proceedings from the International Thermal Spray Conference, 701-705, May 5–8, 2003,
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In order to obtain nano-structured ceramics composite coating for high temperature application, pre-mixed Al 2 O 3 /Y 2 O 3 powders were plasma-sprayed in this study. Plasma spraying of spray-dried Al 2 O 3 /Y 2 O 3 powder resulted in the formation of amorphous coating of metastable Al 2 O 3 -Y 2 O 3 solid solution. After the heat treatment, α-Al 2 O 3 /YAG nano-structured composite coating was successfully obtained via eutectic reaction between Al 2 O 3 and Y 2 O 3 . It was possible to control the sizes of Al 2 O 3 and YAG particles widely by heat treatment with proper condition. Hardness of the coatings showed close relationship with their microstructure.
Proceedings Papers
ITSC 2001, Thermal Spray 2001: Proceedings from the International Thermal Spray Conference, 737-741, May 28–30, 2001,
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The effect of chamber pressure on the temperature and the velocity of the plasma sprayed particles was measured quantitatively through the chamber window. As the chamber pressure increases, the plasma flame shortens. At the same time, the particle slows down and the particle temperature increases. The multivariate analysis among the spray parameters and the measured values reveal that the particle temperature and the particle velocity can be controlled individually as a function of the chamber pressure and the spray distance. The zirconia coatings were fabricated by controlling the particle temperature and velocity at the impinging upon the substrate individually. Increase of the particle temperature increased the deposition efficiency, the density and the hardness of the coating. On the other hand, increase of the particle velocity up to a certain value also increased them, but the excessive velocity decreased them. Because the shortened dwelling time prevented the powder core from melting, even if the surface was sufficiently heated.
Proceedings Papers
ITSC 2001, Thermal Spray 2001: Proceedings from the International Thermal Spray Conference, 49-54, May 28–30, 2001,
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Zircon is widely used as a refractory material, because of its excellent mechanical and chemical properties. Several studies on plasma sprayed zircon were reported since 70's, and it is known that zircon dissociate into silica and zirconia during the plasma spray process. Authors have been studied on plasma sprayed zircon for a protective coating application, and successfully obtained very dense coating with excellent adhesive strength by optimizing the spray parameter. However, it was also revealed that the coating had poor stability above 1500K. In this study, the effects of two different oxides additive (yttria and ceria) on the structure and stability of the plasma sprayed zircon coating above 1500K are evaluated. The addition of these oxides enhanced the amount of residual zirconia and decreased zircon after the heat treatments. Addition of yttria resulted in the coating composed of cubic zirconia and zircon, while monoclinic zirconia was formed by ceria addition.
Proceedings Papers
ITSC2000, Thermal Spray 2000: Proceedings from the International Thermal Spray Conference, 333-339, May 8–11, 2000,
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Effects of spray parameters, such as spray distance, SD, and substrate temperature, Ts, and post heat treatment on the structure and properties of plasma-sprayed zircon coatings were investigated. Zircon was totally decomposed by plasma spray; the coatings were composed of tetragonal zirconia (t-ZrO2) and amorphous silica (a-SiO2), because of the rapid cooling of molten particle right after the impingement to the substrate. Porosity of the as-sprayed coatings was highly affected by both of substrate temperature and spray distance. In all range of the spray distance which had been tried in this study, higher substrate temperature resulted in lower porosity of the coatings; the coating with porosity of 2% was obtained at Ts = 1573K with SD = 95mm. Porosity also decreased with decrease of spray distance. By the heat treatment at 1473K, t-ZrO2 transformed to monoclinic zirconia (m-ZrO2) and a-SiO2 crystallized to cristobalite, respectively. Cracks in the coating disappeared, and open porosity decreased. This can be attributed to sintering of SiO2 and phase transformation of ZrO2. After the heat treatment at 1673K, the coating was composed of ZrSiO4 with dispersed fine m-ZrO2 particle. Open porosity of all the coatings increased up to 10% at this temperature. This is because of volume shrinkage during the formation of zircon.
Proceedings Papers
ITSC2000, Thermal Spray 2000: Proceedings from the International Thermal Spray Conference, 619-624, May 8–11, 2000,
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Alumina matrix composites reinforced with metal thin wire (Inconel-600) were successfully fabricated by plasma spray forming. The atmospheric plasma sprayed matrix layers and wire layers arranged by filament-winding technique were piled up alternately. Though the matrix and the wire were partially bonded only on the side which sprayed particles came flying to, a solid structure was obtained by this technique. Spraying in one direction perpendicular to the substrate made peculiar V-shape pores around the wires, but tilting the torch was effective to reduce the pores. The flexural strength of composite did not increase in spite of some crack deflections on the fracture surface. Owing to the wire pullout, however, the composite exhibited a remarkably higher apparent fracture energy than that of monolithic alumina ceramics.
Proceedings Papers
ITSC1999, Thermal Spray 1999: Proceedings from the United Thermal Spray Conference, 76-81, March 17–19, 1999,
Abstract
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Thermoelectric (TE) power generation from waste heat is recently attracted much attention as one of energy-saving technologies. In this paper, Co-doped n-type iron silicide semiconductor was plasma sprayed under various spray conditions to find the optimum spray-forming conditions. Then Co-doped iron silicide TE device with thickness ranging from 3 to 5 mm and the area of over 100 cm square was produced in the form of a plate or on tube. The paper examines the microstructure and evaluates thermal and electric properties. Paper includes a German-language abstract.
Proceedings Papers
ITSC1999, Thermal Spray 1999: Proceedings from the United Thermal Spray Conference, 265-270, March 17–19, 1999,
Abstract
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Reactive plasma spray is a processing method which combines synthesis and deposition of reaction products in situ. This paper evaluates the effects of the chamber gas pressure, the plasma gas composition and the spray distance on the production of titanium nitrides by means of reactive plasma spraying. It describes and discusses the results obtained from experimental tests for fabrication of titanium/titanium nitride coatings onto steel substrates, with particular reference to the effects of pressure inside the spraying chamber. Paper includes a German-language abstract.
Proceedings Papers
ITSC1998, Thermal Spray 1998: Proceedings from the International Thermal Spray Conference, 1437-1441, May 25–29, 1998,
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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.
Proceedings Papers
ITSC1998, Thermal Spray 1998: Proceedings from the International Thermal Spray Conference, 1443-1448, May 25–29, 1998,
Abstract
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Reactive Plasma Spraying (RPS) is one of several new plasma spray processes. Although several papers have been published on this technology, they are limited in scope to metal powders, such as Ti, Cr, and Si, and coatings composed of metal and non-oxide ceramics. When oxide powders are used among starting materials to fabricate metal or nonceramic coatings, it is important to understand and account for the reduction of oxides during spraying and the chemical reaction among the powder, plasma, and atmospheric gas. The work presented in this paper focuses on the reduction of plasma-sprayed TiO2 and how it is influenced by the amount and type of plasma and chamber gas used, the addition of carbon powder, and process parameters such as chamber pressure.
Proceedings Papers
ITSC1996, Thermal Spray 1996: Proceedings from the National Thermal Spray Conference, 295-302, October 7–11, 1996,
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Plasma sprayed ZrO 2 -CeO 2 and ZrO 2 -CeO 2 -Y 2 O 3 coatings were investigated to develop advanced thermal barrier coating (TBC) with improved thermal and mechanical properties. The addition of a large amount of CeO 2 to ZrO 2 decreased the thermal conductivity, but it also reduced the mechanical property like hardness. Addition of Y 2 O 3 to ZrO 2 -CeO 2 was effective to improve the hardness. Double layered coating composed of a low thermal conductive top layer, such as ZrO 2 -CeO 2 -Y2O 3 and a high strength base layer like yttria stabilized zirconia was fabricated. It exhibited an excellent thermal shock resistance and high thermal barrier capability.