Strength-limiting defects evolved from heterogeneities during the sintering of high-purity submicron alumina powder

Gaku Okuma; Tsukasa Shimizugawa; Shingo Ozaki; Toshio Osada; Shingo Machida; Yutaro Arai; Ryo Inoue; Hideki Kakisawa; Yuki Sada; Masayuki Uesugi; Akihisa Takeuchi; Fumihiro Wakai

doi:10.1016/j.jeurceramsoc.2025.117679

Article Strength-limiting defects evolved from heterogeneities during the sintering of high-purity submicron alumina powder

Gaku Okuma (Research Center for Structural Materials/Materials Manufacturing Field/Ceramic Matrix Composites Group, National Institute for Materials Science) ; Tsukasa Shimizugawa (Yokohama National University) ; Shingo Ozaki (Yokohama National University) ; Toshio Osada (Research Center for Structural Materials/Materials Manufacturing Field/High-Reliability Heat-Resistant Materials Group, National Institute for Materials Science) ; Shingo Machida (JFCC) ; Yutaro Arai (Tokyo university of science) ; Ryo Inoue (Tokyo university of science) ; Hideki Kakisawa (Research Center for Structural Materials/Materials Manufacturing Field/Ceramic Matrix Composites Group, National Institute for Materials Science) ; Yuki Sada (Japan Synchrotron Radiation Research Institute (JASRI)) ; Masayuki Uesugi (Japan Synchrotron Radiation Research Institute (JASRI)) ; Akihisa Takeuchi (Japan Synchrotron Radiation Research Institute (JASRI)) ; Fumihiro Wakai (Research Center for Structural Materials/Materials Manufacturing Field/Ceramic Matrix Composites Group, National Institute for Materials Science)

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Gaku Okuma, Tsukasa Shimizugawa, Shingo Ozaki, Toshio Osada, Shingo Machida, Yutaro Arai, Ryo Inoue, Hideki Kakisawa, Yuki Sada, Masayuki Uesugi, Akihisa Takeuchi, Fumihiro Wakai. Strength-limiting defects evolved from heterogeneities during the sintering of high-purity submicron alumina powder. JOURNAL OF THE EUROPEAN CERAMIC SOCIETY. 2025, 45 (16), 117679. https://doi.org/10.1016/j.jeurceramsoc.2025.117679

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The strength-limiting defects in ceramics evolve from large inhomogeneities, such as agglomerates and aggregates, in the starting powder during sintering. The synchrotron X-ray multiscale tomography (micro-CT and nano-CT) was used to observe how defects evolve from transition alumina aggregates contained in a high-purity submicron α-alumina powder during the sintering. Complex pores, consisting of mutually interconnected pore channels, developed from aggregates through transformation, particle rearrangements, and particle coarsening due to surface diffusion. Under the constraint of the matrix, a circumferential crack was formed partly along the interface between the complex pore and the matrix. The fractography revealed that the fracture origins were complex pores on the fracture surface of bending specimens. The fracture mechanical analysis was conducted to show that both the elliptical crack model and the pore-crack model can explain the mechanical strength.

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