The effects of phase constitution on magnetic and mechanical properties of FeCoNi(CuAl)x (x = 0–1.2) high-entropy alloys

Abstract

In the present work, the effects of phase constitution on the magnetic and mechanical properties of FeCoNi(CuAl)x (x = 0–1.2, in molar ratios) high-entropy alloys (HEAs) have been investigated by using vibrating sample magnetometer (VSM), mechanical tester combined with X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and differential scanning calorimeter (DSC). From the experimental results, the crystallographic structures of FeCoNi(CuAl)x HEAs transform from single face-centered cubic (FCC) phase for 0 ≤ x ≤ 0.6 to body-centered cubic (BCC) phase combined with minor FCC phase for 0.9 ≤ x ≤ 1.2, whereas FCC plus BCC duplex phases are found in the range of 0.7 ≤ x < 0.9. TEM images of FeCoNi(CuAl)0.8 alloy show large numbers of FCC Cu-rich nano-precipitates disperse in the BCC matrix. Furthermore, it is found that the saturation magnetization (Ms) of HEAs with FCC plus BCC duplex structures abnormally increase with the additions of Cu and Al in contrast to single-phase HEAs, showing a linear decrease in Ms. On the other hand, annealing at 573–673 K can lead to a remarkable increase in Ms for FCC plus BCC duplex-phase HEAs other than the single-phase HEAs with almost unchanged Ms. Specifically, annealing under a given condition can lead to the occurrence of phase transition from FCC to BCC phase for FeCoNi(CuAl)0.8 HEAs, resulting in a substantial increase in the Ms from 78.9 Am2/kg to 93.1 Am2/kg and yield strength from 536.7 MPa to 1141.1 MPa. The outreach of the present work might provide a promising way to develop HEAs with a combination of superior magnetic and mechanical properties.