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 Fe_(100−x-y)Cr_(x)Ni_(y)austenitic stainless steels.Cr-rich body-centered-cubic(bcc)precipitates and heterogeneous structure were introduced by cold rolling and annealing at 800℃.Rolling at 700℃ 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.