Y. Tanaka, Y. Himuro, T. Omori, R. Kainuma, Y. Sutou, K. Ishida, K. Yamauchi, Tohoku University, Sendai, Japan
Fe-based shape memory(SM) alloys, such as Fe-Mn-Si[1] and Fe-Ni[2] based alloys, are commercially attractive systems for the practical applications because they are much cheaper and show better workability than Ni-Ti based SM alloys. In particular, Fe-Mn-Si based SM alloys, which exhibit the SM effect associated with γ(FCC) to ε(HCP)martensitic transformation, have been extensively studied and they have been applied for the pipe joining. However, in the Fe-based SM alloys, superelasticity(SE) have not been obtained, which is limited for the practical application.
Recently the present authors have found that Fe-Ni-Co-Al-based alloys undergoes γ(FCC) to α'(BCT) thermoelastic martensitic transformation and exhibits a perfect SM effect, when the alloys are heat-treated under the specific condition and fine particle of ordered g’ (L12-type) phase are precipitated coherently in the austenite matrix. Furthermore, microstructural SE behavior, i.e., a reversible microstructural change during fore- and reverse- transformations due to cycle tensile stress, was confirmed by in-situ observation with optical microscopy and a tensile SE strain of about 1% was obtained at room temperature in the Fe-Ni-Co-Al-based alloys.
[1] A. Sato, E. Chishima, K. Soma, T. Mori, Acta Metall. 30 (1982) 1177.
[2] T. Maki, K. Kobayashi, M. Minayo, I. Tamura, Scr. Metall. 18 (1984) 1105.
Summary: Fe-Ni-Co-Al alloy exhibits the excellent superelaciticity of over 10% by alloying and controlling the microstructure.
