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 → ε martensitic transformation. The effect of temperature on the low-cycle fatigue life (Nf) and the associated plasticity mechanisms of the FMS alloy were evaluated between 253 and 393 K. The longest Nf of 18,029 cycles was obtained at 333 K (at the total strain amplitude of 1%). The Nf 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 Md, respectively). At temperatures below Msσ, the Nf exceeded 5,000 cycles, where ε-martensite was dominant and a long period stacking ordered structure was formed. The longest Nfvalues of over 10,000 cycles were obtained in the dual γ/ε-phase formed between Msσ and Md, while Nf decreased rapidly as the deformation temperature increased beyond Md. The effect of temperature on the Nf of the FMS alloy was comparable to that of Fe–28Mn–6Si–5Cr shape memory alloy, and to the chemical composition dependence of Nf of Fe–30Mn–(6 – x)Si–xAl (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→ε) and the stacking fault energy of austenite (ΓSFE). The superior Nf was associated with the cyclic strain-induced martensitic transformation when ΔGγ→ε was between –50 and 100 Jmol−1, while reversible martensitic transformation relied on a ΔGγ→ε of ∽0 Jmol−1.