Undercooled Melt Formation by Melting of Metastable Eutectic Structure in Al&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;3&lt;/SUB&gt;-Y&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;3&lt;/SUB&gt;-ZrO&lt;SUB&gt;2&lt;/SUB&gt; System

Mizutani, Yukio; Yasuda, Hideyuki; Ohnaka, Itsuo; Sugiyama, A.; Takeshima, Satoshi; Kirihara, Masao; Waku, Yoshiharu

doi:10.2320/matertrans.43.2847

Cited by 12 publications

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“…The selection of the eutectic systems in the present study was consistent with the previous work. 21) Nucleation temperature tended to decrease with increasing cooling rate. As the cooling rate increases, the rate of the heat release increased.…”

Section: Morphological Transition In the Almentioning

confidence: 99%

“…X-ray diffraction patterns of the solidified specimens indicated that the specimens consisted of the metastable eutectic system. According to the previous work, 21) heating the melt up to 2 300 K inhibited the YAG nucleation and the melt was undercooled below the metastable eutectic temperature. The solidification below the metastable eutectic temperature obeyed the metastable eutectic path.…”

Section: Morphological Transition In the Almentioning

confidence: 99%

“…The heating and cooling procedure resulted in the Al 2 O 3 -YAG-ZrO 2 equilibrium eutectic path. 21) The specimens solidified in the equilibrium eutectic system were heated up to temperatures above 2 400 K at a heating rate of 1 K/s, and after holding the melt for 150 s, the specimens were cooled at a given cooling rate. Consequently, the specimen solidified in the Al 2 O 3 -YAP-ZrO 2 metastable eutectic path.…”

Section: Morphological Transition In the Almentioning

confidence: 99%

“…Composition of the specimen used for the DTA measurement was the metastable eutectic composition (Al 2 O 3 -21mol%Y 2 O 3 -12mol%ZrO 2 ), 24) since the fine and uniform metastable eutectic structure was desired for the undercooled melt formation. 21) The powder with the metastable eutectic composition were prepared by using 99.99 % aAl 2 O 3 (2-3 mm diameter), 99.9 % Y 2 O 3 (2-3 mm diameter) and 98 % ZrO 2 (1 mm diameter). Powder was wet ball milled with ethanol to obtain homogeneous slurry.…”

Section: Temperature Measurementmentioning

confidence: 99%

“…21) The undercooled melt produced from the metastable eutectic structure in the heating procedure is attractive for developing a novel solidification processing called the undercooled net shaping. 22) In the proposed processing, it is required to produce the fine and uniform metastable eutectic structure in the green particles.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Morphological Transition In the Almentioning

confidence: 99%

Section: Morphological Transition In the Almentioning

confidence: 99%

Section: Morphological Transition In the Almentioning

confidence: 99%

Section: Temperature Measurementmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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