1998 Fiscal Year Final Research Report Summary
Superplasticity of Non-Equilibrium Materials
| Project/Area Number |
08242107
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| Research Category |
Grant-in-Aid for Scientific Research on Priority Areas
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| Allocation Type | Single-year Grants |
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| Research Institution | Osaka University |
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Principal Investigator |
UMAKOSHI Yuukichi Graduate School of Eng., Osaka University, Prof., 工学部, 教授 (00029216)
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| Co-Investigator(Kenkyū-buntansha) |
KAWAMURA Yoshihito Tohoku Univ. Institute for Mater. Research, Assoc. Prof., 金属材料研究所, 助教授 (30250814)
HIGASHI Kenji Osaka Pref. Univ. Dept. of Metallorgy and Mater. Sci., Prof., 工学部, 教授 (50173133)
HASEGAWA Tadashi Tokyo Univ. of Agriculture and Tech., Fac. of Eng., Prof., 工学部, 教授 (50005328)
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| Project Period (FY) |
1996 – 1998
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| Keywords | high strain rate superplasticity / boundary sliding / dislocation / amorphous alloys / intermetallic compounds / deformation / elongation / fracture |
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| Research Abstract |
Superplastic phenomena in non-equilibrium materials were examined focusing on several factors such as (a) the relation between grain boundary structures and boundary sliding, (b) effect of cavitation on superplastic elongation, and (c) effect of multiplication and annihilation of dislocations. The controlling factors and deformation mechanisms of superplasticity were determined. In addition, new forming processes were developed for industrial applications. The main results obtained during this research term from 1996 to 1998 are as follows.
(1) A special accommodation process to relax the stress concentration at grain boundaries and interfaces is required for high strain rate superplasticity which appeared in ultra fine grained alloys and composites. A liquid phase acts as an accommodation helper. A suitable condition for high strain rate superplasticity was obtained focusing on the strain rate, temperature and the microstructures containing critical size and volume fraction of disperse
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d particles. An appropriate working process is proposed for industrial applications. (2) In micro duplex alloys, small particles not only suppressed the grain growth but also acted as nucleation sources for dislocation multiplication. The motion, multiplication and annihilation of dislocations are very important for high strain rate superplasticity in addition to the grain boundry sliding. (3) On the basis of the dependence of cavitation on the strain rate, temperature and stress-strain curves in Al-Mg-Cu composites consolidated after mechanical griding, effect of grain boundary sliding and deformation in grains on superplasticity was quantitatively evaluated. (4) In Al-Ti intermetallic compound single crystals containing unstable small phases, a new superplastic phenomenon which was independent of the grain boundary sliding was found. The interaction between dislocations and the small secondary phase induced the frequent climb motion and uniform deformation, resulting in the stress accommodation and huge elongation. (5) The characteristics in superplasticity of Pd-, La- and Zr-based amorphous alloys were examined in a wide supercooled liquid region. The superplasticity occurred at a low flow stress of several MPa, 0.6〜0.7 of melting temperature and high strain rate and high m-value of 1 for a Newtonian viscous flow. A new mechanism for the superplasticity was proposed based on the superviscoplasticity. New amorphous alloys showing superplasticity were developed. (6) Industrial technology for working and forming materials using superplasticity was developed and new materials showing superior mechanical and magnetic properties were developed. Less
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