1998 Fiscal Year Final Research Report Summary
Fatigue of Superplastic-Nanocrystals
| Project/Area Number |
09650715
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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 |
Physical properties of metals
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| Research Institution | Kanazawa University |
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Principal Investigator |
VINOGRADOV Alexei Kanazawa University, Department of Mechanical Systems Engineering, Associate Professor, 工学部, 助教授 (10283102)
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| Co-Investigator(Kenkyū-buntansha) |
HASHIMOTO Satoshi Kyoto University, Department of Engineering Physics and Mechanics, Associate Pro, 工学研究科, 助教授 (50127122)
KITAGAWA Kazuo Kanazawa University, Department of Mechanical Systems Engineering, Professor, 工学部, 教授 (30019757)
KANEKO Yoshihisa Kanazawa University, Department of Mechanical Systems Engineering, Research Asso, 工学部, 助手 (40283098)
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| Project Period (FY) |
1997 – 1998
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| Keywords | Ultrafine Grained Material / UFG / Superplasticity / Fatigue / Cyclic Deformation |
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| Research Abstract |
In order to investigate fatigue mechanisms of ultrafine grained materials showing superplasticity at room temperature, we have examined cyclic stress-strain response of (1) single crystal specimens, (2) ultrafine grained copper produced by "Equal Channel Angular Extrusion (ECAE)" method, and (3) Pb-62%Sn and Zn-22%AI alloy fine-grained by the ECAE method.
Fundamental aspects of the cyclic response in crystalline materials were investigated in single- and tr-crystal specimens of copper, Fe-Cr alloy and Fe-Ni-Cr alloy. The single crystal experiments revealed that fatigue deformation gives rise to formations of "persistent slip bands" (PSBs) at a certain range of plastic strain amplitude. The formation of the PSBs induced a drastic changes in Bauschinger energy parameter. In the fatigue tests on the tricrystal specimens, it was experimentally shown that residual stresses between adjoining grains is one-of sources for the Bauschinger effect in the crystalline materials.
in the cyclic deforma
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tion tests on ultrafine grained copper to characterize basic feature of fatigued nano-crystals, following results were obtained. The stress amplitude of the copper fined-grained by the ECAE method became up to 250 MPa. The Bauschinger effect was also significantly high. However, this kind of excellent property of the ultrafine grained copper was very sensitive to heat treatment : both the Stress amplitude and the Bauschinger effect were apparently reduced by an annealing at 200ﾟC.
In the monotonic tensile tests, both the Pb-Sn and Zn-Al specimens showed large elongations even at room temperature. These two materials also showed significant strain-rate dependence of flow stress. In the cyclic deformation tests, the stress amplitudes in the Pb-Sn and Zn-Al alloys were almost saturated from the beginning of the experiments, although a cyclic hardening curve of the annealed copper was divided clearly into the hardening and saturation stages. The stress amplitude and the Bauschinger effect in the Zn-Al alloy apparently increased with increasing strain rate. On the other hand, the Pb-Sn alloy revealed no strain rate dependence of the stress amplitude and the Bauschinger effect. This tendency obtained in the cyclically deformed Pb-Sn alloy is completely different from the result in the monotonic- test. (The cyclic response of the annealed copper was -. independent of the strain rate as well as the yield stress under monotonic deformation.) The absence of the strain-rate dependence in the cyclically deformed Pb-Sn alloy can be attributed to the missing of thermally activated processes which are dominant in the monotonic deformation : the applied plastic strain was probably accommodated substantially by dislocation motion because the plastic strain amplitude is very low with compared to the monotonic deformation. On the other hand, the cyclic deformation in the Zn-Al alloy may involve the thermally activated processes such as dislocation climb and grain boundary diffusion. It is feasible that the plastic strain can not be accommodated only by the dislocation motion because the grain size of the Zn-Al was very small. Less
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