Effects of aging treatment on martensitic transformation of Fe-Ni-Co-Al-Ta-B alloys

The Fe-Ni-Co-Al-Ta-B (notated as NCATB) SMA recently reported by Tanaka et al. exhibits a huge superelastic strain of over 13% through the carefully adjusting martensite transformation from non-thermoelastic to thermoelastic and introduction of a strong recrystallization {0 3 5}(1 0 0) texture by thermomechanical treatment. However, the superelasticity mechanism of this promising novel alloy is still not very clear. In this paper, the effects of aging treatment on martensitic transformation of the metastable NCATB alloy were investigated by means of hardness tests, XRD, 3DAP, and DMA. The hardness tests demonstrated a conventional aging hardening process when the samples were aged isothermally at 923 K. The 3DAP results indicated that the main composition of the gamma' precipitates was Ni, Al and Ta. The DMA results showed that the martensite transformation became more easily with increasing aging time. When the samples were aged at 923 K for 24 h, a premartensitic transformation was also observed in the DMA tests. (C) 2012 Elsevier B.V. All rights reserved.