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Waku, Yoshiharu; Sakata, Sei-ichiro; Mitani, Atsuyuki; Shimizu, Kazutoshi; Hasebe, Mitsuhiro

doi:10.1023/a:1016073115264

Cited by 84 publications

(35 citation statements)

References 13 publications

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“…Another comment in Fig. 4 is that the bending strength does not decrease up to 1873 K, 7) though the strength is much lower than that grown by the micro-pulling-down method below 1500 K. The lower strength below 1500 K may be associated with strain rate dependence for crack initiation and/or propagation, because they carried out the bending tests at a high strain rate.…”

Section: Resultsmentioning

confidence: 94%

“…6 is higher in the growth direction (near a-axis) than in the transverse directions. This result suggests that the scattered deviations from c-axis in the MPD rod;compression by tensilon MPD rod;compression by instron MPD fiber;tension by Lee et al [9] Bridgman;bending by Waku et al [7] Yield or fracture stress,…”

Section: Resultsmentioning

confidence: 94%

“…1) Among them, directionally solidified oxide eutectics, which are called Melt-Growth-Composites (MGCs), are candidate materials to meet the above requirements because of their high strength, excellent oxidation resistance and structural stability up to near their melting temperature. [2][3][4][5][6][7][8][9] It has been reported that the eutectic MGCs having the characteristic complex microstructure [2][3][4][5][6][7][8][9][10][11][12][13] consist of interpenetrating single crystal oxides, [3][4][5][6][7] and show excellent high-temperature performance.…”

Section: Introductionmentioning

confidence: 99%

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Microstructure and High-Temperature Strength of Directionally Solidified Al2O3/YAG/ZrO2 Eutectic Composite

et al. 2004

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The microstructures of an A 2 O 3 /YAG/ZrO 2 eutectic Melt-Growth-Composite (MGC) solidified unidirectionally by the modified-pullingdown method were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and electron backscattered pattern (EBSP) method. The anisotropy of strength was investigated by hardness tests and compression tests at various directions of the composite at elevated temperatures. The eutectic MGC has strong preferred growing orientation and the constituent phases hold the orientation relationship. The eutectic MGC shows excellent high-temperature strength and can deform plastically above about 1500 K. High-temperature strength above 1500 K depends on strain rate, temperature and orientation.

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Section: Resultsmentioning

confidence: 94%

Section: Resultsmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

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Microstructure and High-Temperature Strength of Directionally Solidified Al2O3/YAG/ZrO2 Eutectic Composite

et al. 2004

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“…1) Melt-Growth-Composites (MGC) consisting of oxide eutectics, which are directionally solidified by Bridgman method, are candidate materials to meet the above requirements because of their high strength, excellent oxidation resistance and microstructural stability up to near their melting temperatures. [2][3][4][5][6][7][8][9] Especially, it has been reported that the eutectic MGC, which has the characteristic complex microstructure [2][3][4][5][6][7][8][9][10][11] consisting of interpenetrating single crystal oxides, [3][4][5][6][7] shows excellent high-temperature performance.…”

Section: Introductionmentioning

confidence: 99%

“…The growth direction of Al 2 O 3 in the MPD rod is h300i, 11) which is the same with Al 2 O 3 /YAG or Al 2 O 3 /YAG/ZrO 2 eutectic MGC grown by Bridgman type method. [3][4][5][6][7] However, the MPD rod is anticipated to show finer microstructure and higher strength than the MGC because of a higher solidification rate and a larger temperature gradient in the MPD.…”

Section: Introductionmentioning

confidence: 99%

Texture Control and High-Temperature Strength of Directionally Solidified Al2O3/YAG/ZrO2 Eutectic Composite Rods

et al. 2004

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A 2 O 3 /YAG/ZrO 2 eutectic Melt-Growth-Composite (MGC) rods with two different microstructures were prepared by unidirectional solidification using the modified-pulling-down method (MPD) under different processing parameters. Microstructure and crystallographic texture were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and electron backscattered pattern (EBSP) method. High-temperature strength was evaluated by compression tests at 1773 K and 1873 K. Geometric pattern structure and Chinese script pattern structure are evolved by controlling processing parameters. MPD rods have strong preferred growing orientations in Al 2 O 3 of h001i for the geometric pattern structure and of h300i for Chinese script pattern structure. Constituent phases in the MPD rod hold the orientation relationship. The yield stress for the geometric pattern structure is over 1 GPa at 1773 K, which is extremely higher than that for Chinese script pattern structure. High-temperature strength at 1773 K and 1873 K depends on strain rate and temperature in both the MPD rods.

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Ultra‐High‐Strength Nanofibrillar Al₂O₃–YAG–YSZ Eutectics

et al. 2007

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"Smaller is stronger" is a paradigm in materials development. [1] In the case of metallic materials, the smaller the crystals which make up the material, the more obstacles there are to plastic deformation due to dislocation motion. The utmost limit is found in bulk metallic glasses, which have strengths of up to E/40 (E being the elastic modulus), closer than any other bulk material to the theoretical strength, given by ≈E/20. [2] In ceramic polycrystals, dislocation motion is impeded at ambient temperature, and the strength is controlled by the dimensions of the critical defects. Assuming a semi-circular surface flaw of diameter d, the strength is given byin which K C stands for the fracture toughness; improvements in strength are associated with an increase of the toughness or a reduction of the defect size, which is normally related to the characteristic dimension of the microstructure. Higher toughness in bulk ceramics has been achieved by transformationtoughening of ZrO 2 -based materials [3] or by the self-reinforcement of silicon nitride materials with elongated single-crystal whiskers which led to crack bridging and deflection upon crack propagation.[4] The strength, however, increases linearly with toughness, and the maximum strength of these bulk ceramics was slightly over 1 GPa. Higher strengths could be achieved only by reducing the flaw sizes below the micron size, but the synthesis of bulk nanoceramics with a homogeneous and defect-free (porosity, impurities) microstructure and uniform grain size distribution is still a daunting task, regardless of the recent developments to process nanostructured materials.[5] For instance, pressureless sintering of Al 2 O 3 -based ceramics always leads to grain growth, which limits mechanical properties, and extremely high pressures (as high as 1 GPa) are needed for low temperature sintering. Ultrahard nanoceramics with equiaxed grains were recently produced by devitrification of eutectic corundum-based glasses, [6] and the authors reported a homogeneous microstructure which could be tailored by phase assemblage and heat treatments to a maximum toughness of 4.2 MPam 1/2 , which seems to be the limit for Al 2 O 3 -based nanoceramics.Directionally-solidified eutectics (DSE) are self-organized materials in which phase segregation is driven thermodynamically to produce homogeneous and coherent microstructures. The competition between the flux perpendicular to the growth front with a scale length d C = 2D/m, where D is the diffusion coefficient in the melt and m the growth rate, and the lateral diffusion with a scale length k, the domain size, produces the eutectic morphology that can be controlled by the processing conditions. In particular, k decreases with m according to the equation k 2 m = C (C is a material-dependent constant), [7] and bulk nanostructured ceramics can be obtained in principle by rapid directional solidification from the melt. Under the ideal conditions of coupled eutectic growth, regular eutectic structures can be obtained made up of stacking l...

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Cited by 84 publications

References 13 publications

Microstructure and High-Temperature Strength of Directionally Solidified Al<SUB>2</SUB>O<SUB>3</SUB>/YAG/ZrO<SUB>2</SUB> Eutectic Composite

Microstructure and High-Temperature Strength of Directionally Solidified Al<SUB>2</SUB>O<SUB>3</SUB>/YAG/ZrO<SUB>2</SUB> Eutectic Composite

Texture Control and High-Temperature Strength of Directionally Solidified Al<SUB>2</SUB>O<SUB>3</SUB>/YAG/ZrO<SUB>2</SUB> Eutectic Composite Rods

Ultra‐High‐Strength Nanofibrillar Al₂O₃–YAG–YSZ Eutectics

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Untitled

Cited by 84 publications

References 13 publications

Microstructure and High-Temperature Strength of Directionally Solidified Al<SUB>2</SUB>O<SUB>3</SUB>/YAG/ZrO<SUB>2</SUB> Eutectic Composite

Microstructure and High-Temperature Strength of Directionally Solidified Al<SUB>2</SUB>O<SUB>3</SUB>/YAG/ZrO<SUB>2</SUB> Eutectic Composite

Texture Control and High-Temperature Strength of Directionally Solidified Al<SUB>2</SUB>O<SUB>3</SUB>/YAG/ZrO<SUB>2</SUB> Eutectic Composite Rods

Ultra‐High‐Strength Nanofibrillar Al2O3–YAG–YSZ Eutectics

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Ultra‐High‐Strength Nanofibrillar Al₂O₃–YAG–YSZ Eutectics