Strength and toughness of nanocrystalline SiO₂ stishovite toughened by fracture-induced amorphization

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• 作者：Kimiko Yoshida^a ; Norimasa Nishiyama^b ; Masato Sone^a ; Fumihiro Wakai^a ; ^{wakai.f.aa@m.titech.ac.jp}
• 关键词：Ceramics ; Fracture mechanisms ; Nanocrystalline material ; Phase transformation
• 刊名：Acta Materialia
• 出版年：2017
• 出版时间：1 February 2017
• 年：2017
• 卷：124
• 期：Complete
• 页码：316-324
• 全文大小：2035 K
• 卷排序：124

文摘

The finding of “fracture-induced amorphization” in nanocrystalline SiO2 stishovite lead to a proposal of a new type of transformation toughening by the direct transition from crystal to amorphous state, which is different from the classical martensitic transformation of zirconia. Here, we investigated strength and toughness of nanocrystalline stishovite by using micro-cantilever beam specimens of different sizes. The maximum strength of 6.3 GPa gave the estimate of the lower bound of critical stress for amorphization, which was much higher than the critical transformation stress of zirconia. The crack growth resistance curve (R-curve) rose steeply with crack extension of only a few μm, and reached to a plateau value of 10.9 MPa m1/2. We discussed the effects of grain size, microstrain, and dislocation density on the critical stress, the transformation zone width, and thereby, the fracture toughness.