Effects of Slight Alloying Addition on Fe-Mn-Si-based Shape Memory Alloys

• Main Authors: Tzu-Pin Wang, 王姿蘋
• Other Authors: none
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/81288850417998036049

博士 === 逢甲大學 === 材料科學所 === 98 === 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. Experimental results show that the shape memory effect can be effectively improved by slight addition of Re element. In this study, the Fe69Mn25Si6Re0.11 alloy can exhibit a shape recovery of 96~97%. The annealing treatment at 500~600ºC for the hot-rolled alloys can increase significantly their shape recovery ability. The results show that the SME can be effectively improved by slight addition of rare earth (RE) element. The chromium element can produce grain boundary through the heat treatment. It is important to understand the annealing effects on the shape recovery of these Fe-Mn-Si-Cr alloys. Addition of chromium element could restrain ε martensite and increase corrosion resistance. The phase transformation temperatures for these three specimens were determined by using DSC and reduced martensite start (Ms) temperatures about 60 ℃. This may raise ? austenite matrix. Slight addition of R.E. element can improve the shape memory performance of Fe-Mn-Si and Fe-Mn-Si-Cr alloys and restrain grain boundary. This can increase ε/γ ratios and martensitic transformation temperatures. The Fe-Mn-Si-Cr-RE alloy is the lowest energy and steadiest in these three specimens alloys. It was found that the energy of △HM=5.20J/g and △HA=3.93J/g are lowest in three alloys. Meanwhile, more elements were add, the most entropy cause, and further to make the total Gibbs free energy lowest. This indicates that these secondy precipitates can act as the effective nuclei to enhance the formation of ε martensite, and hence increase the ability of shape recovery. The shape recovery can even reach 97% for the Fe-Mn-Si-Cr-RE specimens. The different strain (0.0%~8.0%) to induced phase transformation was observed by transmission electron microscopy (TEM) and the mechanism of the memory shape effect was also discussed in this study. The results show that the phase of the alloy contained matrix austenite (γ) and thermal-induced martensite two phase structure. When various strain applied on the alloy, it would induce the phase of stress induced martensite (SIM). When the strain is 0.1%, a single orientation stacking faults group can be observed. When the strain is 2.0%, the phase of SIM is main stacking faults group in one orientation. However, the content of main orientation stacking faults group density would increase. When the strain is increasing to about 4%, besides mention above, secondary orientation stacking faults also produce due to adjust higher strain. When the strain is higher than 4%, the phase of SIM would induce many dislocations. The stacking faults broad would increase when the element of Re add into the matrix. The stacking faults group density would increase at the same strain.