Mechanism of training effect in the ferrous shape memory alloys associated with gamma->epsilon martensitic transformation.
Grant-in-Aid for Scientific Research (C).
|Research Institution||Kyoto University|
TSUZAKI Kaneaki Kyoto Univ., Faculty of Eng., Associate Professor, 工学部, 助教授 (40179990)
|Project Fiscal Year
1990 – 1991
Completed(Fiscal Year 1991)
|Budget Amount *help
¥1,700,000 (Direct Cost : ¥1,700,000)
Fiscal Year 1991 : ¥100,000 (Direct Cost : ¥100,000)
Fiscal Year 1990 : ¥1,600,000 (Direct Cost : ¥1,600,000)
|Keywords||Shape memory alloys / gamma->epsilon martensitic transformation / Fe-Mn-Si alloys / Cyclic transformation / Reverse transformation / Training effect / Fe-Mn alloys / Stress-induced epsilon martensite / 形状記憶合金 / γ→εマルテンサイト変態 / FeーMnーSi合金 / 繰り返し変態 / 逆変態 / トレ-ニング効果 / FeーMn合金 / 応力誘起εマルテンサイト / 形状回復率 / εマルテンサイト変態 / マルテンサイト変態 / 形状記憶効果 / 応力誘起マルテンサイト変態|
gamma->epsilon forward and epsilon->gamma reverse transformations and cyclic transformation in Fe-Mn-Si alloys have been investigated. The main findings are as follows.
(1)The change in transformation temperature and microstructure by thermal cycling between room temperature and 573K(above Af)was observed in an Fe-24%Mn-6%Si alloy of which Ms was higher than room temperature. Unlike the case of Fe-24%Mn, Ms hardly changed by the thermal cycling in the Fe-Mn-Si alloy. Moreover, the Fe-Mn-Si alloy showed the good reproducebility of gamma martensite plates, i e., microstructure memory. Furthermore, lattice defects such as dislocations were scarcely observed in the austenite after the thermal cycling. These results strongly suggest that the movement of transformation dislocations is reversible during gamma->epsilon transformations in the Fe-Si-Mn alloy.
(2)Microstructural observation of stress-induced epsilon martensite formed by tensile deformation at room temperature was performed in an Fe
-33%Mn-6%Si alloy of which Ms was just below room temperature. It was confirmed by TEM observation that an epsilon plate formed by the operation of one kind of partial dislocations. A large amount of stacking faults were observed in the untransformed austenite. These stacking faults may act as nucleation sites in the following forward transformation after the annealing above Af. The reversion of stress-induced martensite started at a lower temperature and finished at a higher temperature compared with that of thermally-induced martensite.
(3)The change in shape recovery by the addition of thermal cycling between 77K and 873K to the Fe-33%Mn-6%Si alloy was observed. The shape recovery was not improved by the thermal cycling, indicating that the gamma->epsilon cyclic transformation per se was not associated with the improvement of shape recovery by the training treatment.
It was concluded from the above results that the role of the training effect is to introduce lattice defects into austenite which act as the nucleation sites in the following transformation.
Research Output (7results)