| High-entropy alloys (HEAs) are new kinds of multi-component alloys that were developed in recent years. Differing from traditional alloys, HEAs were loosely defined as the alloys that consist of five or more kinds of elements with equal- or near equal-molar fractions. And through reasonable designed, HEAs can exhibit many special properties, like high strength, high hardness, superconductivity, excellent magnetic property, wear-resistance and corrosion resistance. At present, many HEAs are developed based on AlCoCrFeNi system alloy. Above all, the microstructures and properties have been studied in this paper, through the methods of soft-magnetic B element and hard-magnetic Fe element addition on the AlCoCrFeNi system high-entropy alloy.The HEAs ingots of AlCoCrFeNiBx (x=0,0.01,0.02...0.09,0.1), AlCoCrFeNiBx (x=0, 0.1,0.25,0.5,0.75,1.0) and AlCoCrFexNi (r=0.2,0.4,0.6...2.0) system multi-component HEAs were prepared by vacuum arc furnace under a Zr-gettered high-purity argon atmosphere. X-ray diffractometer (XRD, Shimadzu XRD-6000) with Cu Ka radiation, scanning electron microscope with energy dispersive spectrometry (SEM, Zeiss supra55), compressive properties tester, Vickers microhardness tester model (MH-60) and JDM-13T vibrating sample magnetometer were used for further research of the alloys. The experimental results are as follows:(1) AlCoCrFeNiBx (x=0,0.01,0.02...0.09,0.1) HEAs:as the B contents increasing, the microstructure changed from BCC+B2 mixing structures to BCC+B2+FCC mixing structures. The HEAs exhibited equiaxed-grain morphology, then turned to dendrite structure when x exceeds 0.01. And Grains were obviously refined. With the increase of B contents, the hardness also exhibited a tendency of first increasing from HV486.7 to HV502.4, and then declining to HV460.7. The compressive fracture strength firstly showed a trend of increasing, and then, when x exceeded 0.08, declined. The coercive forces and the specific saturation magnetizations of the alloys decreased as B contents addition, the decreasing coercive forces showed a better soft magnetic behavior.(2) AlCoCrFeNiBx (x=0,0.1,0.25,0.5,0.75,1.0) HEAs:The AlCoCrFeNi high entropy alloy exhibited equiaxed-grain morphology, then turned to dendrite structure when B content, x=0.1. The microstructures changed from B2+BCC structures to B2+BCC+FCC structures, finally formed B2+BCC+FCC and borides mixing structures. And the hardness declined from HV486.0 to HV460.7, then rose to HV615.7 as the addition of B element. The lowest hardness value was obtained when x=0.1. The compressive fracture strength shows a distinct decrease with B addition. The maximum compression strength was 2227 MPa when x=0. But when x reached 0.75, the samples fractured during the elastic deformation due to the formation of hard and brittle borides. The coercive forces and the specific saturation magnetizations of the alloys decreased as the contents B element increased. The decreasing coercive forces showed a better soft magnetic behavior.(3) AlCoCrFexNi (x=0.2,0.4,0.6...2.0) HEAs:as Fe contents increasing, the microstructures changed from Cr3Ni2+B2+BCC structures to B2+BCC mixing structures as x exceeds 0.8. And the hardness declined from HV637.2 to HV460.2 as the addition of Fe element. The lowest hardness value was obtained when x=2.0. When x=0.2, the alloy exhibited dendrites morphology, but as Fe contents increased, the AlCoCrFexNi system HEAs all turned to equiaxed-grains morphology. There were little changes for the fracture strength, but an increase for plastic property. It should be attributed to the decrease of lattice distortion. |
PDF Full Text Request