Microstructural Evolution and Mechanical Behavior of Co‐Free (Fe₄₀Ni₃₀Cr₂₀Al₁₀)_100−xTi_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)₉₆Ti₄ 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)₉₆Ti₄ 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.