Preparation And Wave-absorbing Properties Of AlCoFeCr System High-entropy Alloys

With the tremendous development of wireless communication technology in military and civilian applications,wave-absorbing materials play an important role in various applications such as military stealth technology,precise positioning systems,and electromagnetic interference protection.High-entropy alloys（HEA）are promising materials for application as microwave absorbents owing to their durability in harsh environments and multiple mechanisms for the attenuation of electromagnetic fields.In this paper,Al Co Fe Cr system high-entropy alloy powders were prepared by mechanical alloying,and the phase structure,microscopic morphology,magnetic properties,and electromagnetic properties of the alloy powder were analyzed.The wave-absorbing properties and wave-absorbing mechanisms of three high-entropy alloy powders in the Al Co Fe Cr system,Al_1.5Co₄Fe₂Cr,Al_1.5Co₄Fe₂Cr Cu_x,and Al_1.5Co₄Fe₂Cr/RGO,were investigated.The results of the study showed that:（1）The Al_1.5Co₄Fe₂Cr high-entropy alloy powders have soft magnetic properties and exhibit a single BCC phase structure.The Al_1.5Co₄Fe₂Cr high-entropy alloy powders prepared by ball milling at 70 h and 350 rpm,respectively,had highε″andμ″values and exhibited good electromagnetic absorption ability.Annealing leads to a reduction in the internal stress of the alloy powders and an increase in grain size and crystallinity,resulting in a further increase in magnetic loss capacity.After annealing,the impedance matching is optimized.The minimum reflection loss of the annealed Al_1.5Co₄Fe₂Cr alloy powders prepared by ball milling for 70 h increased from-20.30 d B to-26.13 d B at 1.40 mm thickness,and the effective absorbing bandwidth increased from 3.29 GHz to 4.55 GHz and reached 6.40 GHz at 1.60 mm thickness,achieving the best match between thickness and bandwidth.（2）The phase structure of Al_1.5Co₄Fe₂Cr Cu_x high-entropy alloy powders prepared by ball-milling for 70 h is a simple BCC phase and an FCC phase.The alloy powders have high saturation magnetization strength（M_s）and low coercivity（H_c）as well asε″andμ″values.The increase in Cu content leads to a decrease in M_s value and an increase in H_c value.When the molarity of Cu is 1,the Al_1.5Co₄Fe₂Cr Cu high-entropy alloy powders exhibit good wave absorption properties.The dispersion makes the agglomeration of Al_1.5Co₄Fe₂Cr Cu_x alloy powders weaker,which helps enhance the electromagnetic absorption performance of the alloy powders.（3）Al_1.5Co₄Fe₂Cr/RGO alloy powders are soft magnetic powders.The phase structure is a simple solid solution BCC phase,and the phase appearance appears as irregular flakes,grains,and ellipsoidal shapes.Compared with the alloy powders before compounding RGO,the complex dielectric constantε′value of the powders after compounding RGO increases,and the dielectric loss capability is enhanced.With the increase of ball milling speed,ε′value,μ′value,andμ″value all show the trend of increasing and then decreasing.The minimum reflection loss of Al_1.5Co₄Fe₂Cr/RGO alloy powders increased in absolute value,and the wave-absorption performance was enhanced when the ball milling speed was 350 rpm.