2005 Fiscal Year Final Research Report Summary
The Characteristics and Mechanisms of Ultra-Fine Grained Structure Formation during Severe Large Deformation.
| Project/Area Number |
16560627
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Material processing/treatments
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| Research Institution | The University of Electro-Communications |
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Principal Investigator |
SAKAI Taku The University of Electro-Communications, Faculty of EC, Professor, 電気通信学部, 教授 (40017364)
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| Project Period (FY) |
2004 – 2005
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| Keywords | Hot working / Warm and cold working / Multidirectional forging / Microshear band / kink bands / Grain fragmentation / Continuous recrystallization / Fine-grained structure |
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| Research Abstract |
The process and mechanisms of fine-grained structure formation during severe large deformation was studied in multi-Directional forging (MDF) and a single pass compression at ambient and high temperatures by using Al, Mg and Fe alloys. The relationships between deformation characteristics and evolution process of microstructures were analyzed, and the main results obtained were summarized as follows.
1.The volume fraction of new fine-grained structure evolved by MDF increases more rapidly with deformation compared with that in a single pass compression. Increase in a strain per each MDF results in rapid evolution of finer grained structure in lower strain.
2.During a single pass compression, in contrast, new grains are developed only along the original grain boundaries and fine layered microstructures are formed in the grain interiors.
3.Several kinds of deformation bands such as microshear and kink bands are generated in grain interiors in above a critical strain. The density and the misorientations of their boundaries increase with straining, leading to fragmentation of original grain interiors and finally formation of new fine-grains. The process of such strain-induced grain formation is concluded to be controlled by in-situ or continuous dynamic recrystallization.
4.Deformation bands are developed in various directions in three-dimensional space during MDF, leading to formation of fine-grained structures in large strain. This means that MDF is one of effective methods for fine-grained structure formation.
5.Annealing of such strain-induced grain structure can not be controlled by conventional discontinuous recrystallization including nucleation and growth of new grains, but also by in-situ or continuous static recrystallization, in which grain growth takes place accompanied with recovery.
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