Tuning Cr-rich nanoprecipitation and heterogeneous structure in equiatomic CrFeNi medium-entropy stainless alloys

High-/medium-entropy stainless alloys (HESAs/MESAs) are a new kind of alloys with great potential to combine excellent properties from high-/medium-entropy alloys (HEAs/MEAs) and stainless steels. A CrFeNi MESA was chosen to investigate its microstructures and mechanical behaviors. After homogenization, the strength and ductility of CrFeNi MESAs with single-phase face-centered-cubic (fcc) structure were higher compared with those of Fe100−x–yCrxNiy austenitic stainless steels. Cr-rich body-centered-cubic (bcc) precipitates and heterogeneous structure were introduced by cold rolling and annealing at 800 °C. Rolling at 700 °C results in higher dislocation density and the occurrence of lamellar Cr-rich bcc precipitates. High-density dislocations and fcc grains with heterogeneous structure, together with Cr-rich bcc precipitates, contribute to a yield strength improvement of about 50 MPa, and appreciable tensile yield strength of ~ 540 MPa and fracture strain of ~ 20% are obtained. It reveals that not only compositional variations but also grain size and phase structure tuning can be utilized for achieving desired mechanical properties.