トレーニング処理によるFe-32Mn-6Si合金の形状記憶効果の向上とその異方性

抄録

The improvement of shape memory effect due to the austenite (γ)_??_epsilon (ε) martensitic transformations and the development of its anisotropy by training treatment were studied by using an Fe-32Mn-6Si alloy. The training treatment of five times repetitions of 2% tensile deformation at 300K and heating up to 723K was given to the solution-treated samples. By this treatment, lots of stacking faults are introduced in the samples. The test specimens were cut from the trained plates either parallel (0°sample) or vertical (90°one) with respect to the training direction.
In the 0° samples the pre-existing stacking faults are found to be very effective not only to produce the stress-induced ε martensite but also to increase the γ strength against usual slip. A seemingly one thick ε plate has been revealed to consist of nano-scale γ/ε lamellar structure which is preferable to hold the back stress. The shape recovery improved due to the reversible motion of Shockley is partial dislocations assisted by this back stress. The recovery stress for backward motion of Shockley partial dislocations during the ε→γ reversion is found to increase markedly by the training treatment.
On the other hand, in the 90°samples, the pre-existing stacking faults are of no use to enhance the stress-induced εmartensitic transformation and they rather hinder the transformation. Intersections of ε/ε plates and/or ε plates/stacking faults were frequently observed. Since the γ is almost equally strengthened in the 0° and 90°samples by the training, the slight increase in the shape recovery strains in the 90°samples compared with the non-treated samples is presumably resulted from the existence of higher back stress.