Microstructure And Properties Of AlCrFe₂Ni₂B_x High-entropy Alloy

High-entropy alloys（HEAs）are an emerging class of alloys with multiple elements as primary elements,which have received wide attention from researchers because of their excellent mechanical properties,such as high strength,high hardness,high corrosion resistance and irradiation resistance.In this paper,the cobalt-free Al Cr Fe₂Ni₂ HEA is used as the research object.Although its strength-plasticity match is good,it still has the problem of low yield strength,so the addition of B element is chosen to enhance the yield strength.And systematically explores the microstructure,mechanical properties,and corrosion resistance of the Al Cr Fe2Ni2Bx（x=0,0.01,0.02,0.04,0.08,0.1,0.2,0.5）HEAs.The results of the tissue analysis showed that the phase composition of the alloy did not change with the increase of B element content,but there was obvious boride precipitation;the microstructure was transformed from a tissue with obvious grain boundaries to a dendritic tissue,and the interdendritic region increased with the increase of B element content.This transformation process is accompanied by a significant refinement of the grain size.The results of room-temperature and low-temperature mechanical tests showed that the yield strength of the Al Cr Fe₂Ni₂B_x HEAs increases with the increase of B element content at room temperature,and when the B element content is added to x=0.08,the Al Cr Fe₂Ni₂B_0.08 alloy shows the most excellent overall mechanical properties,with a yield strength of about 937 MPa,which is about 32%higher than that of the Al Cr Fe₂Ni₂ alloy without B element.At 173 K,with the increase of B element content,the yield strength of the Al Cr Fe₂Ni₂B_x HEAs showed the same trend as that at room temperature,but the yield strength of Al Cr Fe₂Ni₂B_0.08 alloy increased to about 1338MPa,which was about 43%higher than that at room temperature environment;The yield strength of Al Cr Fe₂Ni₂B_0.08 HEA is about 1641 MPa at 77K,which is about 16%higher than that at 173 K and about 75%higher than that in the room temperature environment.This is due to the interaction force between the soft FCC phase and the hard BCC phase within the alloy due to the inconsistent deformation during the deformation process as the temperature decreases,with the soft FCC phase providing deformation and the hard BCC phase providing strength,enabling the material to have both high strength and high plasticity,thus achieving a perfect match between strength and plasticity.The results of the corrosion resistance tests showed that the Al Cr Fe₂Ni₂ alloy showed the worst corrosion resistance in 3.5%Na Cl solution,with the largest corrosion current density of 2.466×10^-7μA/cm² and the smallest charge transfer resistance of1.598×10⁵Ω·cm².With the increase of B element content,the corrosion resistance of the Al Cr Fe₂Ni₂B_x HEAs were enhanced,and when it was increased to x=0.1,the Al Cr Fe₂Ni₂B_0.1 alloy showed the most excellent corrosion resistance,with the smallest corrosion current density of 2.011×10^-8μA/cm² and the largest charge transfer resistance of 2.595×10⁶Ω·cm².Continuing to increase the content of element B,the corrosion resistance decreases,but is still higher than that of the alloy without the addition of B element.