Specimen size dependence of strength and fracture toughness of extrinsically brittle metals

2015 Fiscal Year Final Research Report

• Project/Area Number: 26630347
• Research Category: Grant-in-Aid for Challenging Exploratory Research
• Allocation Type: Multi-year Fund
• Research Field: Structural/Functional materials
• Research Institution: Kyoto University
• Principal Investigator: Okamoto Norihiko 京都大学, 工学(系)研究科(研究院), 助教 (60505692)
• Project Period (FY): 2014-04-01 – 2016-03-31
• Keywords: 微小寸法試料 / サイズ依存性 / 集束イオンビーム(FIB)法 / ナノ結晶 / 超微細粒多結晶 / 銅 / パルス電析法

Outline of Final Research Achievements

Although most pure metals such as aluminum, copper and so on are intrinsically ductile, they are known to become brittle when the crystal grain size is considerably reduced. It had remained an open question if these extrinsically brittle metals exhibit any specimen size dependence of strength and fracture toughness. In the present research, we have performed compression tests and bending tests for micrometer-sized specimens of nanocrystalline copper fabricated by pulsed electrodeposition. We have revealed that when the crystal grain size is reduced down to 34 nm, where the dislocation motion is difficult, the specimen size dependence of strength disappears in contrast to the coarse grained polycrystalline copper, and that the brittle fracture behavior, which is observed when the bulk nanocrystalline copper is bent, disappears and turns to be ductile when the specimen size is reduced to the micrometer size.

Free Research Field

金属材料，金属物性