| Project/Area Number |
14550693
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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 |
Structural/Functional materials
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| Research Institution | Ritsumeikan University |
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Principal Investigator |
AMEYAMA Kei Ritsumeikan Univ., Fac Science and Engineering, Professor, 理工学部, 教授 (10184243)
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| Project Period (FY) |
2002 – 2003
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| Project Status |
Completed (Fiscal Year 2003)
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| Budget Amount *help |
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 2003: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2002: ¥2,300,000 (Direct Cost: ¥2,300,000)
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| Keywords | Powder Metallurgy / Steels / Mechanical Alloying / Nano structure / Stacking Fault Energy / Phase Transformation / Austenitic Stainless Steel / NIckel / 超強化工 / ステンレス鋼 / 超微細結晶粒 / ナノ構造制御 / 微細組織 / SUS316 / フェライト |
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| Research Abstract |
Formation mechanism and microstructure of severe plastic deformed materials such as 5U5316L austenitic stainless steels and Nickel are studied. Mechanical Milling (MM) process is one of the severe plastic deformation (SPD) process which enables to produce an ultra fine grain structure. By the TEM, formation of an equiaxed grain structure with high dislocation density and its grain size of less than 100 nm are observed. The SADP demonstrates that the microstructure consists of FCC and BCC crystal structures. These FCC and BCC grains show almost the same grain size, however, the image of the BCC grain is more spherical and more clear than that of the FCC grain. In other words, compared to the BCC grain the FCC grain has more irregular grain boundary and more complex strain contrast. The Vickers hardness tests of as homogenized, as milled and annealed (at 358 K (85 degree C) for 5 mm or 1 hr) powders indicates a large decrease in the hardness after annealing at 358 K. The results strongly suggest that there must exist of a huge number of vacancies to cause such a low temperature recovery. These results also imply that the BCC phase appears by means of a diffusionless transformation. Although the austenite phase in the 5U5316L steel is meta-stable at the room temperature, it hardly transforms to martensite phase even by a heavy deformation. Thus, the BCC phase is considered to form by a massive-like ferrite transformation. The spherical shape of the ferrite grain is attributed by the nucleation and growth of the massive ferrite grain. The increase of lattice defects, which leads to low temperature recovery, and formation of the irregular grain boundary structure result in increase of driving force for the transformation of austenite to ferrite.
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