添加微量Re對Fe-Mn-Si基形狀記憶合金影響之研究

Abstract

Fe-Mn-Si基形狀記憶合金具有加工性良好、價格低廉等特性，在套筒元件的接合與應用具有其優勢。本實驗於具有良好形狀記憶能力的Fe-Mn-Si基合金中，嘗試添加微量錸(Re)元素，經過不同熱處理後，進行形狀記憶效應與微結構之檢測分析，並針對其中幾組合金作熱機訓練與相關效應之探討。實驗結果顯示：各組不同比例合金中以Fe-25Mn-6Si-5Cr合金添加0.11 wt. %的錸元素、經熱輥壓與600~700℃兩小時的退火處理後，其形狀回復率表現最好。熱滾狀態下之合金，內部有過多差排存在，且其ε�γ偏高，而當退火溫度高於800℃時發生再結晶而使基地強度下降，這些因素將造成合金形狀回復率之降低。Fe-25Mn-6Si-5Cr合金在回復溫度500℃、最大拉伸應變為2%、3%下進行熱機訓練，應力-應變曲線為循環硬化，形狀回復率隨著循環次數的增加而遞減。Fe-25Mn-6Si-5Cr-0.11Re在同樣條件下進行熱機訓練，其應力-應變曲線為循環軟化，形狀回復率隨著循環次數的增加而遞增，經六次熱機訓練後即接近100%之形狀回復。

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.