Low-cycle fatigue life and plasticity mechanisms of a Fe−15Mn−10Cr−8Ni−4Si seismic damping alloy under cyclic loading at various temperatures

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 ( N _f) and the associated plasticity mechanisms of the FMS alloy were evaluated between 253 and 393 K. The longest N _f of 18,029 cycles was obtained at 333 K (at the total strain amplitude of 1%). 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 ( M _s ^σ and M _d, respectively). At temperatures below M _s ^σ, the N _f exceeded 5,000 cycles, where ε-martensite was dominant and a long period stacking ordered structure was formed. The longest N _f values of over 10,000 cycles were obtained in the dual γ/ε-phase formed between M _s ^σ and M _d, while N _f decreased rapidly as the deformation temperature increased beyond M _d. 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– 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 (Δ G ^γ→ε ) and the stacking fault energy of austenite (Γ _SFE). The superior N _f was associated with the cyclic strain-induced martensitic transformation when Δ G ^γ→ε was between –50 and 100 Jmol ⁻¹, while reversible martensitic transformation relied on a Δ G ^γ→ε of ∽0 Jmol ⁻¹.