Effect of Annealing on Microstructure, Mechanical Properties and Thermal Conductivity of (Ni₅Al₂)_100-xFe_x (x = 35, 40, 45 and 50) Eutectic Medium Entropy Alloys

In this paper, dual-phase (Ni₅Al₂)_100-xFe_x (x = 35, 40, 45 and 50) eutectic medium entropy alloys (EMEAs) were prepared by vacuum arc melting. Also, the effect of annealing treatment on microstructure and properties of the alloys was further investigated. Results show that the eutectic microstructure of (Ni₅Al₂)_100-xFe_x EMEAs consisted of FCC and BCC phases at as-cast state and ordered L1₂ phase precipitated from FCC phase after annealing at 700 °C for 1 h, which induced the abnormal increments of strength and thermal conductivity after annealing. For as-cast (Ni₅Al₂)₅₅Fe₄₅ EMEA, the tensile strength and elongation were 991 MPa and 24.1%, respectively. After annealing, its tensile strength and elongation were 1279 MPa and 22.4%, respectively. For as-cast (Ni₅Al₂)₆₀Fe₄₀ EMEA, the thermal conductivity at room temperature, 200, 400 and 600 °C was 10.83, 13.06, 15.95 and 18.94 W/(m·K), respectively. After annealing, its thermal conductivity at room temperature, 200, 400 and 600 °C was 23.92, 25.12, 26.51 and 31.39 W/(m·K), respectively.