T. Sawaguchi et al. / Scripta Materialia 99 (2015) 49–52
Designing Fe–Mn–Si alloys with improved low-cycle fatigue lives
Takahiro Sawaguchi, Ilya Nikulin, Kazuyuki Ogawa, Kaoru Sekido, Susumu Takamori, Tadakatsu
Maruyama, Yuya Chiba, Atsumichi Kushibe, Yasuhiko Inoue and Kaneaki Tsuzaki
Paper6Survey
Advisor : 戴子堯
Reporter : 李懋靖
Department of Mechanical Engineering
& Institute of Nanotechnology,
Southern Taiwan University of Science and Technology,
Tainan, TAIWAN
Date ﹕2015/12/29
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Outline
Introduction
Design
Experiment
Conclusion
Introduction
Recently, Sawaguchi et al. proposed that Fe–Mn–Si based alloys can be used for
the seismic damping of architectural constructions.
Seismic metallic dampers absorb the vibrations of buildings through elastoplastic
deformation;however, severe deformations cause fatigue in the damper metal.
An Fe–Mn–Si-based alloy with the chemical composition of Fe–28Mn–5Cr–6Si–
0.5NbC (in wt.%) was reported to exhibit a stable damping capacity associated
with reversible martensitic transformations under cyclic push–pull loading.
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Introduction
This stable deformation behaviour with enhanced fatigue properties makes
such alloys highly suited for use in seismic dampers, in particular against longduration ground motion.
For this purpose, we attempted to develop new Fe–Mn–Si-based alloys with
enhanced low-cycle fatigue (LCF) lives,N𝑓 .
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Design
The central idea behind the design concept is the reversibility
of the plasticity mechanisms characteristic of low-SFE alloys.
Figure 1 illustrates schematic models of the reversible
dislocation motions associated with (a, b) a deformationinduced 𝛾 − 𝜀 martensitic transformation,
(c,d) deformation 𝛾-twinning and (e, f) extended dislocation
gliding.
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Design
Figure 1. Schematic diagrams of the reversible group motion of the dislocations in (a, c, e)
tension and (b, d, f) compression. (a, b)
Deformation-induced 𝜀-martensitic transformation, (c, d) mechanical 𝛾-twinning, (e, f)
extended dislocation gliding.
The dashed and solid lines represent {111} planes of the 𝛾-crystal and stacking faults,
respectively.
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Experiment
Table 1. Chemical compositions, the number of cycles to fatigue fracture, 𝑁f , the stress
amplitude and the hysteresis energy at 𝑁f /2, ∆𝜎/2Nf/2 and ∆𝑊Nf/2 , respectively.
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Experiment
Figure 2. The composition dependence of LCF and its thermodynamic
properties.
(a–d) 𝑁f , (measured), (e–h) SFE (calculated) and (i–l) volume fractions
(measured) of the 𝜀- and 𝛼(𝛼’)-phases before deformation (f(𝜀)INT and
f(𝛼)INT) and after fatigue fracture (f(𝜀)FF and f(𝛼)FF).
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Experiment
Figure 3. Post-fatigue-fracture microstructures of the Fe–Mn–Cr–Ni–Si alloys.
EBSD phase maps (step size: 0.4 𝜇m) and TEM images for (a,d) s = 0, (b, e) s = 4 and (c, f) s = 6.
The areas in white and grey in the EBSD images are the 𝛾- and 𝜀-phases, respectively, and blue lines
represent low-angle boundaries (misorientation ranging from 2 to 15).
Cubes and hexagons in the figures represent the orientations of the 𝛾- and 𝜀-phases.
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Conclusion
In conclusion, we propose two design criteria for improving the
LCF lives of Fe–Mn–Si-based alloys:
first,a thermodynamic balance between 𝛾- and 𝜀-phases is essential to promote the reversible movement of Shockley partials;and secondly, a moderate planarity of dislocation motion
aided by solute atoms is needed for further improvement.
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Thanks for your attention !!
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