Effect Of Refractory Metal Addition On The Formation And Properties Of FeCoNiBSi High-Entropy Bulk Metallic Glass

Metallic glasses（MGs）have high strength,high elasticity and excellent corrosion resistance due to the structural characteristics of long-range disordered atomic arrangement,and exhibit unique advantages as new structural or functional materials.However,the MGs are metastable materials,and when the temperature is higher than the crystallization temperature,they will crystallize and fail,which limits the application at high temperatures.Due to the multi-principal high-entropy effect,high-entropy metallic glasses（HE-MGs）show better thermal stability and ability against crystallization than traditional MGs composed of one dominant component.Increase of the entropy is an effective method to enhance the thermal stability and slow down the crystallization rate of the MGs.In addition,addition of refractory metals（RMs）or metalloids to the MGs has also been found to be effective to improve the thermal stability and strength.In order to further improve the thermal stability and expand the application of the MGs to high temperature field,in this work,the RMs like W,Mo,Nb,and Ta were added into a Fe₃₀Co₂₅Ni₂₀(B_0.7Si_0.3)₂₅ HE-MG developed in the previous stage,the effects of the RMs on the thermal properties,glass-forming ability（GFA）,mechanical properties,corrosion resistance and magnetic properties of the HE-MGs were investigated,the mechanism of the RMs addition to enhance the thermal stability and GFA was discussed,and the effect of annealing on the structure,mechanical properties and magnetic properties of a Fe₃₀Co₂₅Ni₁₅Ta₅(B_0.7Si_0.3)₂₅ HE-MG were investigated.The main findings are as follows:1.Adding of 5 at.%W,Mo,Nb,and Ta,respectively,to the Fe₃₀Co₂₅Ni₂₀(B_0.7Si_0.3)₂₅HE-MG can improve the thermal stability and GFA.Among them,the Fe₃₀Co₂₅Ni₁₅Ta₅(B_0.7Si_0.3)₂₅ HE-MG has the highest glass transition temperature（T_g）,crystallization onset temperature（T_x）,and the critical diameter for glass formation（d_c）,and its T_g,T_x and supercooled liquid region（ΔT_x）are 818 K,867 K,and 49 K,respectively,which are much higher than those of 772 K,805 K,and 33 K,respeceively for the Fe₃₀Co₂₅Ni₂₀(B_0.7Si_0.3)₂₅,and the d_c increases from 1 mm to 2.5 mm.The improvement of thermal stability and GFA of alloy by RM element originates from the formation of Fe23C6-type complex competing crystal phase and the increase of atomic size mismatch and chemical affinity between alloy components.2.The addition of the RMs improves the strength and corrosion resistance of the Fe₃₀Co₂₅Ni₂₀(B_0.7Si_0.3)₂₅ high-entropy bulk metallic glass（HE-BMG）.The yield strength（ζ_y）of the Fe₃₀Co₂₅Ni₁₅Ta₅(B_0.7Si_0.3)₂₅ HE-BMG increases from 3225 MPa to 4189 MPa,accompanied by a certain compressive plasticity,and the Vickers microhardness（Hv）increases from 941 to 1309.The self-corrosion potential of the HE-BMG in 3%Na Cl solution increases from-0.32 V to-0.12 V,the corrosion current density decreases from 8.2×10^-7A/cm² to 2.5×10^-7 A/cm²,and the corrosion rate reduces from 9.0×10^-3 mm/a to 1.6×10^-3mm/a.In addition,Fe₃₀Co₂₅Ni₁₅RM₅(B_0.7Si_0.3)₂₅ HE-MGs exhibit soft magnetic properties with saturation magnetic inductionof 0.72-0.76 T and coercive force of 1.4-2.8 Am^-1.3.No obvious crystal diffraction peaks were observed in the XRD spectrum of the Fe₃₀Co₂₅Ni₁₅Ta₅(B_0.7Si_0.3)₂₅ HE-BMG after isothermal annealing at 817-867 K for 15 min.Combined with the DSC results,it is speculated that the nanocrystals with a volume fraction of below 7%were precipitated after isothermally annealing at 842 K for 15 min.At this time,the Hv andζ_y of the alloy are 1469 and 4261 MPa,respectively,which are 160 and 72 MPa greater than those of the as-quenched alloy,respectively.The volume fraction of nanocrystalline phase was 12%after annealed at 817 K for 30 min,and the Hv andζ_y of the alloy are 1478 and 4276 MPa,respectively.