Low-Cycle Fatigue Life and Plasticity Mechanisms of a Fe−15Mn−10Cr−8Ni−4Si Seismic Damping Alloy Under Cyclic Loading at Various Temperatures

Abstract

A recently developed Fe−15Mn−10Cr−8Ni−4Si (FMS) seismic damping alloy has a superior fatigue life at room temperature due to reversible dislocation motion associated with the γ → e martensitic transformation. The effect of temperature on the low-cycle fatigue life (N f) and the associated plasticity mechanisms of the FMS alloy were evaluated between 253 and 393 K. The longest (N f of 15,644 was obtained at 313 K. The (N f was dependent on the plasticity mechanisms, which were subdivided into three temperature regions with respect to the upper temperature limits for stress-assisted and strain-induced martensitic transformation (Msσ and Mdσ, respectively). At temperatures below Msσ, the Nf exceeded 5,000 cycles, where e-martensite was dominant and a long period stacking ordered structure was formed. The longest Nf values of over 10,000 cycles were obtained in the dual γ/e-phase formed between Mdσ and Mdσ, while Nf decreased rapidly as the deformation temperature increased beyond Mdσ. The effect of temperature on the N f of the FMS alloy was comparable to that of Fe–28Mn–6Si–5Cr shape memory alloy, and to the chemical composition dependence of N f of Fe–30Mn–(6 – x)Si–x Al (x= 0-6) transformation- and twinning-induced plasticity (TRIP/TWIP) steels. A new set of thermodynamic parameters was established to calculate the Gibbs free energy difference between the phases (ΔGγ→e) and the stacking fault energy of austenite (ΓSFE). The superior N f was associated with the cyclic strain-induced martensitic transformation when ΔGγ→e was between –50 and 100 Jmol-1, while reversible martensitic transformation relied on a ΔGγ→e of ~0 Jmol-1.