Stepwise regulation of phase structure and strength–ductility synergy in FeCrNi-based medium-entropy alloys via Cu and Ti

Based on the design concept of “low-cost, Co-free, and multiscale,” we successfully fabricated an as-cast (Fe40Cr35Ni20Cu5)97Ti3 alloy through a Cu–Ti stepwise alloying strategy. The alloy exhibits a dual-phase FCC/BCC matrix containing nanoscale precipitates within the BCC phase. Our study reveals that the addition of 5 at. % Cu increases the FCC phase fraction, enhancing the elongation from 18% to 32%, while inducing core–shell structured nanophases within the BCC matrix and maintaining the yield strength at 560–600 MPa. The subsequent addition of 3 at. % Ti increases the BCC phase fraction, further strengthening the matrix, and transforms the core–shell structures into homogeneously distributed nanoparticles. Through this synergistic control over phase fraction and precipitate characteristics, the as-cast alloy achieves a yield strength of 1043 MPa, a tensile strength of 1337 MPa, and an elongation of 12%. This work deepens the understanding of the synergistic regulation of Cu and Ti on microstructure and mechanical properties and provides guidance for developing high-performance Co-free casting alloys.