Microscopic toughening mechanism toward the nano-micro hierachical microstructural design for high toughness and high strength

2017 Fiscal Year Final Research Report

• Project/Area Number: 16K14411
• Research Category: Grant-in-Aid for Challenging Exploratory Research
• Allocation Type: Multi-year Fund
• Research Field: Structural/Functional materials
• Research Institution: Tokyo Institute of Technology
• Principal Investigator: Wakai Fumihiro 東京工業大学, 科学技術創成研究院, 教授 (30293062)
• Project Period (FY): 2016-04-01 – 2018-03-31
• Keywords: 破壊靱性 / 強度 / ミクロ力学試験 / セラミックス / ナノ結晶材料 / 靱性強化機構

Outline of Final Research Achievements

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 andtoughness 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 micrometers, and reached to a plateau value of10.9 MPa m1/2. The results clearly showed this novel toughening mechanism can achieve both excellent strength and toughness.

Free Research Field

無機材料：物性