Effects of Thermally Induced Cyclic γ ↔ ε Transformation on Shape Memory Effect of a Quenched FeMnSiCrNi Alloy

Abstract

The effects of thermally induced cyclic g $ e transformation on microstructures and shape memory effect (SME) are investigated in a quenched Fe14Mn5.5Si8.0Cr5.0Ni alloy. The results show that the annealing at 773 K remarkably improves the SME in the quenched alloy. One thermal cycling between 290 and 773 K remarkably increases the SME, but the further thermal cycling hardly improves the SME. The reason is that the amount of thermal e martensite remarkably reduces after annealing at 773 K, but it hardly changes with the further increase of thermal cycling between 290 and 773 K. The pre-existing thermal e martensite not only prevents the occurrence of stress-induced e martensitic transformation but also promotes the formation of a 0 martensite. ADVANCED ENGINEERING MATERIALS 2013, 15, No. 8

Origin of shape memory effect in Co–Ni alloys undergoing fcc⇌hcp martensitic transformation

“…It can be expected that the strengthening of matrix by other methods, such as solution, dispersion and grain refinement hardening, will improve their SME. 16 2) The pre-existing thermal hcp martensite can strengthen the matrix of the Co-30.3Ni alloy and thus promotes the formation of the stress-induced hcp martensite. This is the reason that the SME in the Co-30.3Ni alloy increases with the rise in the amount of thermal hcp martensite.…”

“…Because a good shape memory effect (SME) can been obtained in Fe-Mn-Si-based alloys showing the same martensitic transformation [10][11][12][13][14][15][16], thus, it can been expected that a good SME should be obtained in the Co-Ni alloys. On the other hand, both the fcc and the hcp phases are ferromagnetic in the Co-Ni alloys [1], but, in contrast, they are both paramagnetic in the Fe-Mn-Si-based alloys [10].…”