Effects of plasticity-induced martensitic transformation and grain refinement on the evolution of microstructure and mechanical properties of a metastable high entropy alloy

•Structures of metastable austenite (γ) and stable sigma (σ) and martensite (ε) in Fe42Mn28Co10Cr15Si5 alloy are characterized.•Content of phases and grain structure were tailored by rolling and friction stir processing to enhance strength.•Tremendous microstructural flexibility exhibited by the alloy facilitated fabrication of the alloy with strength of 1850 MPa.•Strain to fracture of the material is greater with a larger amount of the γ phase and a slower rate of γ→ε transformation.•Rate of transformation increases with the initial content on γ and preferential texture relative to compression direction.