Study On Nd₂₀Pr₂₀RE₂₀Fe₂₀Co₁₀Al₁₀ （RE=La/Ce/Y） High-entropy Alloy With Hard Magnetic Properties

As a new kind of material,high entropy alloy（HEA）has attracted much attention because of its unique structure and special properties.Magnetic HEAs usually exhibit soft magnetic property.However,there are few investigations on HEAs with hard magnetic property.Hard magnetic materials are widely used and are essential functional materials in industrial production.It is of great significance to develop HEAs with hard magnetic properties.New hard magnetic Nd₂₀Pr₂₀RE₂₀Fe₂₀Co₁₀Al₁₀（RE=La/Ce/Y）HEAs were developed by replacing Nd elements in Nd₆₀Fe₂₀Co₁₀Al₁₀bulk amorphous alloy（BAA）with Pr and La/Ce/Y elements.The microstructure and composition of the new HEAs were detected by X ray diffraction（XRD）,scanning electron microscope（SEM）,transmission electron microscope（TEM）;the magnetic and mechanical properties of the new alloys were tested by vibrating sample magnetometer（VSM）and Tribo indenter.Meanwhile,the coercive force(H_cj)mechanism and magnetic viscous behavior of the alloys are analyzed.The main research work and conclusions in this thesis are as follows:（1）The Nd₂₀Pr₂₀RE₂₀Fe₂₀Co₁₀Al₁₀（RE=La/Ce/Y）alloys show hard magnetic properties,indicating the new hard magnetic HEAs have been successfully prepared.The Nd₂₀Pr₂₀La₂₀Fe₂₀Co₁₀Al₁₀ alloy shows the best comprehensive magnetic properties of three alloys,the coercivity(H_cj),saturation magnetization（M_s）and curie temperature（T_C）are 280 k A/m,13.94 Am²/kg and 467.9 K,respectively.（2）The mechanical properties of Nd₂₀Pr₂₀RE₂₀Fe₂₀Co₁₀Al₁₀（RE=La/Ce/Y）alloy have been studied.The Nd₂₀Pr₂₀Y₂₀Fe₂₀Co₁₀Al₁₀ alloy shows the highest elastic modulus（E_r）and Hardness,which is 63.7 GPa and 4.8 GPa,respectively.The Nd₂₀Pr₂₀La₂₀Fe₂₀Co₁₀Al₁₀ alloy shows the lowest E_r and Hardness,which is 58.7 GPa and 3.7 GPa,respectively.（3）Three new alloys are all composed of two kinds of amorphous phases with compositional fluctuation and crystalline phase.The two amorphous phases of Nd₂₀Pr₂₀La₂₀Fe₂₀Co₁₀Al₁₀ and Nd₂₀Pr₂₀Ce₂₀Fe₂₀Co₁₀Al₁₀ alloys are distributed alternately,and there are some nanocrystals on the amorphous matrix.The two amorphous phases of Nd₂₀Pr₂₀Y₂₀Fe₂₀Co₁₀Al₁₀ alloy are separated,and large size grains are exist on the amorphous matrix.（4）The coercivity of Nd₂₀Pr₂₀La₂₀Fe₂₀Co₁₀Al₁₀ and Nd₂₀Pr₂₀Ce₂₀Fe₂₀Co₁₀Al₁₀ alloys come from the combination of magnetic interaction and strong domain walls pinning;but the H_cj of Nd₂₀Pr₂₀Y₂₀Fe₂₀Co₁₀Al₁₀ alloy only comes from the domain walls pinning.The magnetic interaction comes from two kinds of amorphous phases in the alloy.The pinning center of the domain walls pinning is the nanocrystals embedded on the amorphous matrix.（5）The magnetic viscosity behavior of Nd₂₀Pr₂₀RE₂₀Fe₂₀Co₁₀Al₁₀（RE=La/Ce/Y）alloys were studied,and the thermal fluctuation field（Hf）,activation volume（ν_a）,domain wall width（δ_w）and the maximum pinning force per unit pinning center（f）were calculated.It was found that if the size of the nanocrystals are similar to theδ_w,the f will be high,and the H_cj of the alloy are higher.