Microstructural Evolution and Mechanical Behavior of Co-Free (Fe40Ni30Cr20Al10)100-x Ti x High-Entropy Alloys

In this work, microstructural evolution and mechanical behavior of Co-free (Fe40Ni30Cr20Al10)(100-x )Ti (x) (x = 0, 2, 4, 6, and 8 at%) high-entropy alloys (HEAs) are investigated. All as-cast HEAs consist of face-centered-cubic (FCC)- and body-centered-cubic (BCC)-structured phases, wherein the BCC-structured phase is composed of disordered BCC (A2) and ordered BCC (B2) phases. The HEAs show FCC dendrite and BCC inter-dendrite microstructure when x <= 4. As the Ti content increases to 6 and 8 at%, the microstructure evolves from dendrite structures to complex lamellar structures, leading to a significant loss in ductility. With the increase of Ti, the strength is enhanced with the sacrifice of ductility. The (Fe40Ni30Cr20Al10)(96)Ti-4 alloy exhibits promising combinations of strength and ductility, displaying a yield strength of 680 MPa, an ultimate tensile strength of 1132 MPa, and a total elongation of 16.6%. The simple FCC + BCC dendrite microstructure and optimal content of the BCC-structured region containing A2 + B2 phases are responsible for the excellent tensile properties of the as-cast (Fe40Ni30Cr20Al10)(96)Ti(4 )HEA. In this work, it is suggested that good combinations of strength and ductility of low-cost Co-free FeNiCrAl-based HEAs can be achieved by tailoring Ti addition.