The astonishing effect of Si addition on low-cycle fatigue life in a metastable high-entropy alloy

Abstract

The effect of Si content on the tensile and cyclic deformation behavior of Fe50-xMn30Co10Cr10Six (x = 0–6) as a metastable high-entropy alloy (HEA) was investigated in this study. Heat treatment at 1100 °C for 30 min led to a single-phase microstructure (γ) with a face-centered cubic crystal structure and an average grain size of ∼50 μm in the cold-rolled specimens. The similar tensile properties and the same amount of ε after tensile tests in 0Si and 4Si alloys show that up to 4 at. % of Si the deformation mechanisms were not significantly affected. However, the cyclic deformation behavior was very sensitive to the Si content. The initial cyclic hardening decreased by adding Si and the cyclic softening stage was replaced by stress saturation or secondary hardening. Moreover, the γ to ε-martensite phase transformation that is accompanied by contraction in the unit cell volume of γ was facilitated by adding Si in cyclic loads. These phenomena resulted in the fatigue lives more than 10000 cycles at Δεt= 0.7% that were not reported up to now at this strain amplitude in HEAs. Although the stacking fault energy might be lowered by adding Si, the fatigue life enhancement by adding Si attributes more to the beneficial effect of Si on the reversibility of γ↔ε phase transformation.