Preparation, Properties And Structure Of Fe-Y-B Based Bulk Metallic Glasses

Fe-based metallic glasses have attracted much attention for cheap cost,high mechanical properties,excellent sofimagnetic properties and corrosion resistance. However,their industrial application is largely restricted for intrinsic brittleness or poor glass forming ability(GFA) of ferromagnetic Fe-based metallic glasses.Thus it is important to develop Fe-based bulk metallic glasses(BMGs) with both excellent GFA and good sofimagnetic properties.First of all,a new quaternary Fe-M-Y-B(M=Si,Ti,Zr,Cr,AI,Co,Ni,W,Mo and Nb) BMGs system was developed on the basis of Fe-Y-B ternary alloy.It is found that minor addition of Me(Me=W,Mo and Nb) enhance GFA largely,which could be attributed to the optimization of atomic radius distribution and the formation of reinforced backbone structure to increase the thermal stability of supercooled liquid. The maximum size of fully glassy rods increases from 2mm for Fe₇₂Y₆B₂₂ to 4mm for Fe₆₈W₄Y₆B₂₂ and 5ram for Fe₆₈Mo₄Y₆B₂₂ and Fe₆₈Nb₄Y₆B(22).Moreover,the new-developed BMGs demonstrate excellent mechanical and good sofimagnetic properties,i.e.,high compression strength of 4011MPa,low coercive force of 1.6A/m and saturated magnetization of 0.77T for Fe₆₈W₄Y₆B₂₂ glassy rods.Secondly,the quinary Fe-Mo-Y-B-M(M=Co,Ni,Ti,Zr,Er,Dy and Cr) BMGs alloy system was developed based on the composition of Fe₆₈Mo₄Y₆B₂₂.It is found that minor addition of all these elements except for Cr deteriorates the GFA in the investigated composition range,while the substitution of 1at.%Cr for Y enhance the GFA.Using copper mould casting,glassy cylindrical rods with 6mm in diameter were successfully synthesized with the nominal composition of Fe₆₈Mo₄Cr₁Y₅B₂₂.At the same time,minor addition of Cr is capable of improving the corrosion resistance of glassy alloy in 3%NaCI and 0.5M Na₂SO₄ solution.Additionally,anomalous glass transition in the supercooled liquid region of Fe-Mo-Y-B BMGs was carefully elucidated using differential scanning calorimetry (DSC) and extended X-ray absorption fine structure(EXAFS) methods.It is concluded that the anomalous inflection could be due to the overlapping of endothermic peak characteristic of glass transition and exothermal peak characteristic of structural evolution of chemical short-range ordering.The chemical short-range ordering might be attributed to strong interaction between metal atoms(Mo,Y and Fe) and metalloid atoms(B),combined with repulsive force between Mo and Y.From the aspect of local atomic structure,the effect of minor Y addition on the glass formation ability was investigated utilizing EXAFS simulation.It is proposed that in Fe-Y-B ternay alloy,Y atoms with large atomic radius tend to occupy the 8c site in complex Fe₂₃B₆ structure and constrain the precipitation of simple crystalline phase,i.e.,FeaB.When Y content is close to the maximum value of 8c site provided by Fe₂₃B₆,excessive internal stress and lattice distortion introduced by Y atoms might lead to the instability of Fe₂₃B₆ competition crystalline phase and enhance the stability of supercooled liquid,eventually favoring the formation of amorphous state during solidification.