Fatigue crack growth behavior of the quaternary 3d transition metal high entropy alloy CoCrFeNi

[Display omitted] •Fatigue crack growth behavior of CoCrFeNi characterized.•Presence of crack stepping during fatigue crack growth identified.•At high ΔK, localized areas of deformation twinning was observed. CoCrFeNi, a 3d transition metal high entropy alloy, has shown promising mechanical and corrosion resistance properties. CoCrFeNi was subjected to tension–tension fatigue at room temperature and the steady-state fatigue crack growth characteristics and underlying deformation mechanisms were investigated. CoCrFeNi exhibited good steady-state fatigue crack growth resistance with the Paris law exponent at the lower end of the ductile metals range, m ≈ 2.5, regardless of load ratio. TEM analysis performed at different locations revealed that the plastic deformation mechanism changed from dislocation slip to the addition of nano-twinning as ΔK increased over crack life.