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Waku, Yoshiharu; Nakagawa, Narihito; Wakamoto, Takumi; Ohtsubo, Hideki; Shimizu, Kazutoshi; Kohtoku, Yasuhiko

doi:10.1023/a:1004486303958

Cited by 120 publications

(54 citation statements)

References 9 publications

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“…For example, unidirectionally solidified Al 2 O 3 -YAG (Y 3 Al 5 O 12 , yttrium-aluminum-garnet) eutectic composites have high strength, thermal stability, creep resistance, and corrosion resistance at high temperatures. [1][2][3][4][5][6][7][8] The Al 2 O 3 -GAP (GdAlO 3 , gadolinium-aluminum-perovskite) eutectic composites produced by melt growth have a flexural yield stress of about 700 MPa, and display some plastic deformation rather than brittle fracture at 1873 K. 9) In the case of the Al 2 O 3 -EAG (Er 3 Al 5 O 12 , erbium-aluminum-garnet) eutectic composites, a flexural strength of 300-350 MPa and excellent thermal stability at 1973 K in an air atmosphere has been reported. 10) Furthermore, research on eutectic composites has been extended to pseudo-ternary systems.…”

Section: Introductionmentioning

confidence: 99%

Undercooled Melt Formation by Melting of Metastable Eutectic Structure in Al2O3-Y2O3-ZrO2 System

et al. 2002

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This paper presents a selection of the eutectic systems in the Al 2 O 3 -Y 2 O 3 -ZrO 2 pseudo-ternary system and the production of the undercooled melt due to melting of the metastable eutectic structure at the metastable eutectic temperature. In the pseudo-ternary system, there are two eutectic systems; one is the Al 2 O 3 -YAG(Y 3 Al 5 O 12 )-ZrO 2 equilibrium system and the other is the Al 2 O 3 -YAP(YAlO 3 )-ZrO 2 metastable system. The eutectic system was selected by maximum melt temperature before solidification. YAG nucleation was inhibited in the melt when heated above 2250 K and consequently the metastable eutectic solidification path was selected. The selection controlled by the melt temperature before solidification was similar to that of the Al 2 O 3 -Y 2 O 3 system. Furthermore, the undercooled melt formation was found when the Al 2 O 3 -YAP-ZrO 2 metastable eutectic structure was heated up to temperatures above the metastable eutectic temperature. The addition of ZrO 2 to the Al 2 O 3 -Y 2 O 3 system inhibited the YAG nucleation remarkably and enhanced the undercooled melt formation in comparison with the Al 2 O 3 -Y 2 O 3 pseudo-binary system. Ease of the undercooled melt formation in the pseudo-ternary system will be beneficial for the melt shaping processes.

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Section: Introductionmentioning

confidence: 99%

Undercooled Melt Formation by Melting of Metastable Eutectic Structure in Al2O3-Y2O3-ZrO2 System

et al. 2002

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“…Recently, eutectic ceramic composites produced by unidirectional solidification have been taken into attention as a candidate for high temperature materials, [11][12][13][14][15][16] since the Al 2 O 3 -YAG (Y 3 Al 5 O 12 , yttrium-aluminum-garnet) eutectic structure that consists of Al 2 O 3 single crystal and YAG single crystal exhibits desirable for high temperature materials. Besides the high temperature properties, the Al 2 O 3 -Y 2 O 3 system has unique properties in solidification.…”

Section: Techniquesmentioning

confidence: 99%

“…Recently, eutectic ceramic composites produced by unidirectional solidification have been taken into attention as a candidate for high temperature materials, [11][12][13][14][15][16] 17) there are two eutectic reactions in the Al 2 O 3 -rich portion. One is the equilibrium eutectic reaction of Al 2 O 3 -YAG at 2 099 K and the other is the metastable eutectic reaction of Al 2 O 3 -YAP (YAlO 3 , yttrium-aluminumperovskite) at 1 975 K. Solidification in the metastable eutectic path normally occurs when the melt is once heated up to temperatures above 2 273 K. [17][18][19] Heating the melt above 2 273 K seemed to inhibit YAG nucleation in the liquid.…”

Section: Introductionmentioning

confidence: 99%

Application of an Optical DTA for Morphological Transition in the Al2O3-YAP-ZrO2 Metastable Eutectic System

et al. 2003

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This paper presents an optical DTA apparatus which is capable to examine the solidification behavior of the Al 2 O 3 -based materials. A direct current through the two Mo crucibles effectively heats specimen and reference up to 2 400 K. The small heat capacity of the crucible and the specimen enabled a cooling rate up to the order of 10 2 K/s. Since accuracy of temperature measurement by two two-color pyrometers was not affected by emissivity change to phase transformation, exothermic and endothermic heats in the specimen was efficiently detected at high temperatures. The developed apparatus was used to examine DTA for aAl 2 O 3 and the Al 2 O 3 -YAP-ZrO 2 metastable eutectic system. The morphological transition from the entangled eutectic structure to the lamellar eutectic structure was observed at a cooling rate around 10 K/s. At a cooling rate more than 70 K/s, a-Al 2 O 3 phase started to solidify as a primary phase. Furthermore, the divorced eutectic solidification was recognized at a cooling rate of 360 K/s. KEY WORDS: differential thermal analysis (DTA); solidification; ceramics; phase transformation; morphological transition. techniques.Recently, eutectic ceramic composites produced by unidirectional solidification have been taken into attention as a candidate for high temperature materials, [11][12][13][14][15][16] since the Al 2 O 3 -YAG (Y 3 Al 5 O 12 , yttrium-aluminum-garnet) eutectic structure that consists of Al 2 O 3 single crystal and YAG single crystal exhibits desirable for high temperature materials. Besides the high temperature properties, the Al 2 O 3 -Y 2 O 3 system has unique properties in solidification. According to a phase diagram reported by Caslavsky and Viechnicki,17) there are two eutectic reactions in the Al 2 O 3 -rich portion. One is the equilibrium eutectic reaction of Al 2 O 3 -YAG at 2 099 K and the other is the metastable eutectic reaction of Al 2 O 3 -YAP (YAlO 3 , yttrium-aluminumperovskite) at 1 975 K. Solidification in the metastable eutectic path normally occurs when the melt is once heated up to temperatures above 2 273 K. [17][18][19] Heating the melt above 2 273 K seemed to inhibit YAG nucleation in the liquid. The experimental results suggested the existence of an irreversible change at temperatures above melting point. However, there is still ambiguity regarding the irreversibility of the change because of the difficulties of thermodynamic measurement. Thus, it is expected that the DTA is used for understanding the unique solidification behavior. However, there was no conventional apparatus to measure the heat release from the specimen at the high temperatures up to 2 400 K. The requirement for the thermal analysis at the high temperatures motivated to develop a DTA technique.In addition, it has been found that heating the metastable eutectic up to temperatures above the metastable eutectic temperature but the equilibrium eutectic temperature produced the undercooled melt for the Al 2 O 3 -Y 2 O 3 system 20) and the Al 2 O 3 -Y 2 O 3 -ZrO 2 system.21) The undercool...

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“…Los compuestos cerámicos eutécticos Al 2 O 3 -ZrO 2 (Y 2 O 3 ) y Al 2 O 3 -Y 3 Al 5 O 12 (YAG) procesados mediante técnicas de solidificación direccional se caracterizan por presentar excelentes propiedades de fluencia [1][2][3] junto con una buena estabilidad microestructural y resistencia a la degradación ambiental cuando están expuestos a elevadas temperaturas durante largos períodos de tiempo [4][5][6]. Su elevada resistencia mecánica a temperaturas altas ha recibido muy poca atención y los resultados disponibles en la literatura son contradictorios.…”

Section: Introductionunclassified

Propiedades mecánicas de cerámicos eutécticos Al2O3-ZrO2 (Y2O3) y Al2O3-YAG procesados por solidificación direccional

Pastor¹,

Oliete²,

Salazar³

et al. 2005

Bol. Soc. Esp. Ceram. Vidr.

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procesados por la técnica de fusión zonal asistida por láser en el intervalo de temperaturas de 25ºC a 1427ºC. Se ha investigado el efecto de la microestructura, de las tensiones residuales y de la temperatura sobre la resistencia a flexión y los mecanismos de fractura asociados para cada material. [1][2][3] junto con una buena estabilidad microestructural y resistencia a la degradación ambiental cuando están expuestos a elevadas temperaturas durante largos períodos de tiempo [4][5][6]. Su elevada resistencia mecánica a temperaturas altas ha recibido muy poca atención y los resultados disponibles en la literatura son contradictorios. La resistencia mecánica de muestras masivas (0.3-0.4 GPa) se mantiene hasta temperaturas muy elevadas (1600-1700ºC en el caso de Al 2 O 3 -YAG [7][8]). En cambio, este mismo material en forma de fibras con diámetros de 100-200 µm y con resistencias del orden de 1 GPa a temperatura ambiente presenta una degradación considerable a 1100-1400ºC [3,9]. Esta degradación ocurre debido a la nucleación de defectos superficiales, caracterizados por una microestructura gruesa, y que resultan de las reacciones químicas con impurezas procedentes del ambiente y que contienen Si [3][4]. La presente investigación tiene por objetivo analizar con más detalle los factores que controlan la resistencia mecánica a elevadas temperaturas de barras de Al 2 O 3 -YAG y Al 2 O 3 -ZrO 2 (Y 2 O 3 ) procesadas mediante la técnica de fusión zonal asistida por láser. 2.-ProceSAdoLos materiales se fabricaron utilizando polvos comerciales de Y 2 O 3 (Aldrich 99%), Al 2 O 3 (Aldrich 99%) y ZrO 2 (Alfa 99%). Se prepararon tres tipos de mezclas de polvos con distintas composiciones. La primera mezcla corresponde a la composición eutéctica del sistema alúmina/ytria y contenía 81.5% mol de Al 2 O 3 y 18.5% mol de Y 2 O 3 . Las dos mezclas siguientes corresponden a la composición eutéctica del sistema alúmina/zirconia con dos contenidos diferentes de ytria. En un caso la mezcla de polvos presentaba un 62% mol de Al 2 O 3 , 37.81% mol de ZrO 2 y 0.19% mol de Y 2 O 3 , y en el otro la mezcla estaba formada a partir de 62% mol de Al 2 O 3 , 33.44% mol de

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Untitled

Cited by 120 publications

References 9 publications

Undercooled Melt Formation by Melting of Metastable Eutectic Structure in Al<SUB>2</SUB>O<SUB>3</SUB>-Y<SUB>2</SUB>O<SUB>3</SUB>-ZrO<SUB>2</SUB> System

Undercooled Melt Formation by Melting of Metastable Eutectic Structure in Al<SUB>2</SUB>O<SUB>3</SUB>-Y<SUB>2</SUB>O<SUB>3</SUB>-ZrO<SUB>2</SUB> System

Application of an Optical DTA for Morphological Transition in the Al2O3-YAP-ZrO2 Metastable Eutectic System

Propiedades mecánicas de cerámicos eutécticos Al<sub>2</sub>O<sub>3</sub>-ZrO<sub>2</sub> (Y<sub>2</sub>O<sub>3</sub>) y Al<sub>2</sub>O<sub>3</sub>-YAG procesados por solidificación direccional

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