Preparation And Properties Of High-stability Iron-based Bulk Metallic Glass

Fe-based bulk metallic glasses have the characteristics of high strength,low cost,good corrosion resistance and soft magnetic properties,which make them have a broad application prospect in the field of structural and functional materials.However,Fe-based metallic glasses are metastable materials from the thermodynamics,and will inevitably lose their unique properties due to the structural evolution in the long-term service environment.Therefore,how to maintain the structural stability of Fe-based metallic glasses to expand their application area is an important subject in this field.In addition,Fe-based metallic glasses also have relatively poor glass forming ability.To overcome these difficult problems,the development of Fe-based bulk metallic glasses with few components is one of the most promising ideas.The occurrence of new Fe-based bulk metallic glasses with few components not only can enrich the type of Fe-based metallic glasses,but also helps to understand the formation mechanism of metallic glass.Therefore,the development of new Fe-based bulk metallic glasses with low component and high stability have long been the focus of attention in the field,which has important scientific significance and practical value.It is well known that there is a positive correlation between the thermal stability of metallic glass and its melting point.Among the Fe-based metallic glasses,the Fe B type metallic glasses always have a relatively high thermal stability.Therefore,the introduction of high melting point elements into the Fe B metallic glass is expected to develop high stability Fe-based metallic glasses.Based on this,the new Fe-W-B ternary Fe-based bulk metallic glasses with the reasonable composition design was developed.The structure,thermal stability,mechanical behavior and corrossion resistance of these alloys were then systematically investigated by X-ray diffraction（XRD）,optical microscope（OM）,scanning electron microscope（SEM）,transmission electron microscope（TEM）,differential heat analyzer（DTA）,microhardness tester,electrochemical workstation and universal material testing machine.According to these detailed investigations,the following important results have been obtained:1.Through reasonable composition design,the new ternary Fe-W-B bulk metallic glasses have been developed.The specific components with the critical size of 1mm are:Fe₅₉W₂₃B₁₈,Fe₆₁W₂₀B₁₉,Fe₆₃W₁₉B₁₈,Fe₆₄W₁₉B₁₇,Fe₆₆W₁₈B₁₆.The Fe-W-B bulk metallic glasses have the highest thermal stability in the ternary system of Fe-based bulk metallic glasses（the glass transition temperature T_g was 923 K,the onset crystallization temperature T_xalso exceeded 970 K）,meanwhile it had the high hardness of 1400 HV.This is mainly attributed to the strong chemical bonds formed by the W element with other elements,thus effectively stabilize the atomic structure of metallic glass.The corrosion current density of Fe₆₄W₁₉B₁₇ alloy was 2.15×10^-5A/cm² and the passivation region was close to 2 V.The analysis shows that the passivation film is composed of Fe O and WO₃.2.The effect of Cr replacing Fe on the stability of Fe-W-B bulk metallic glasses was systematically studied.The results show that with the increase of Cr（x=0.05,0.1,0.15,0.2）,the glass forming ability of Fe-W-B alloy was decreased,but the thermal stability and corrosion resistance were improved obviously,which the T_g was954 K,T_xwas 994 K,and the hardness exceeded 1500 HV of the(Fe_0.9Cr_0.1)₅₉W₂₃B₁₈bulk metallic glass.Compared with Fe,Cr tends to form strong Cr-B bond with B due to its lower electronegativity,which makes Fe Cr WB alloy have high thermal stability and hardness.In addition,the corrosion resistance of the alloy was significantly improved by Cr replacement.The improvement of corrosion resistance is mainly attributed to the formation of Cr oxide Cr₂O₃ during the corrosion process,which promotes the formation of the more compact passivation film and further hinders the ionic exchange during the corrosion process.3.Fe_1-xCo_x-W-B（x=0.1,0.2,0.3,0.4,0.5）bulk metallic glasses were prepared by replacing Fe with similar element Co.It was found that the glass forming ability was gradually improved with the increase of Co,and the critical diameter of(Fe_0.5Co_0.5)₅₉W₂₃B₁₈ alloy was better than 1.5 mm.However,the glass formation ability of the Fe-W-B bulk metallic glasses were greatly reduced when the Fe element was substituted by similar Ni element,even for the Fe_0.9Ni_0.1-W-B alloy with x=0.1.The analysis shows that this is mainly caused by the difference of competitive crystalline phases brought by the addition of Co and Ni.The addition of Co promotes the precipitation of Co WB,Co W₂B₂ and other phases,and increases the types of competitive phases.For Fe Ni WB alloy,the main crystalline phase precipitated is fcc-（Fe,Ni）phase with simple structure,and the complexity of atomic arrangement is obviously reduced.Therefore,atoms are more likely to diffuse and rearrange in the solidification process of alloy melt,which worsens the glass forming ability.In addition,it has been found that Co can improve the corrosion behavior of Fe-W-B bulk metallic glasses,which is mainly attributed to the hindrance of charge transfer and the inhibition of diffusion by the Co oxide generated during the corrosion process.However,the corrosion resistance of the Ni replaced alloy deteriorates due to the precipitation of a large number of crystalline phases,which destroys the structural homogeneity of the alloys.The new Fe-W-B ternary metallic glasses developed in this work possess high thermal stability,hardness and good corrosion resistance due to the introduction of a large amount of refractory metal W（～20 at.%）,which not only enriches the understanding of the formation mechanism of Fe-based bulk metallic glass,but also provides a reference for the development of long-term service of metallic glass in high temperature,complex media and other harsh environments.