Effects of Slight Re Addition on the Fe-Mn-Si Based Shape Memory Alloys
Date Issued
2007
Date
2007
Author(s)
Lo, Pang-Chieh
DOI
zh-TW
Abstract
The use of Fe-Mn-Si based shape memory alloys is important to the petroleum pipe industry because of low prize、good workability and shape memory effect (SME). In this study, we added slight Rhenium (Re) in Fe-Mn-Si based alloys and annealed in different temperatures. We analyzed the microstructure, hardness, composition, and other phenomenons after Re added. Finally, we tried to improve the SME by thermo-mechanical treatment.The experiment results showed that the recovery ratio of Fe-25Mn-6Si-5Cr-0.11Re achieve 97% under the condition of 700℃ annealing. Adding amount of Re and annealing temperatures are the main reasons which addect the SME. When Re added over 0.15wt.%, it generally causes the low recovery ratio. The best annealing treatment range is 600℃ to 800℃. Once treatment over 800℃, Fe-Mn-Si based alloys began to recrystallize and decrease hardness.The phase transformation causes the shape recovery. X-ray diffraction showed that γ and ε proportion changed after Re added. Ratio of γ and ε can explain the condition of low SME. The ratio ε╱γ dropped after added 0.11wt.% Re in the alloys. To the contrary, after added over 0.15wt.% Re, ε╱γ was too high to harm the SME.The second phase particle formed at the grain boundaries after heat treatment. This phase can be found obviously from 600℃ to 800℃ heat treatment and it has similar mechanical properties to the matrix. From the study, the second phase affected SME slightly.Shape memory effect can be improved by thermo-mechanical treatment. The stress-strain curve of Fe-25Mn-6Si-5Cr will change from “cyclic hardening” to “cyclic softening” after 0.11wt.% Re added. When the curve presents “cyclic softening”, it means the shape recovery will increase with training times. The recovery ratio can achieve 100% after 4~6 training times.
Subjects
Fe-Mn-Si形狀記憶合金
錸(Re)元素
熱機訓練
Fe-Mn-Si based shape memory alloys
Rhenium(Re)
themo-mechanical training
Type
thesis
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