Preparation,structure And Magnetic Properties Of Fe-Ni-Co-B-Si-Cu-Zr Amorphous And Nanocrystalline Alloys

As one of the magnetic materials,amorphous and nanocrystalline alloys have attracted more and more attentions in the fields of science and technological applications owing to their excellent magnetic properties.Great progress has been made both in basic research and practical application for the amorphous and nanocrystalline alloys.In aspect of the basic research,the theoretical knowledge of magnetism has been deeply studied,and the trinciples of composition design have been explored,which laid a good foundation for the practical application of amorphous and nanocrystalline alloys.In aspect of the practical application,the preparation technology has been optimized,and the new technologies have been developed,which made the amorphous and nanocrystalline alloys been used in wider fields.More and more amorphous and nanocrystalline alloys have been widely used in the fields of transformers,sensors,magnetic shielding,data storage,microwave communication and electronic information.Comparing with the traditional magnetic materials,amorphous and nanocrystalline alloys possess their own advantages,but there are still disadvantages.Therefore,further research for amorphous and nanocrystalline alloys is necessary.The composition is the prerequisite for materials to obtain their desired magnetic properties by controling the preparation process,and the microstructure of the materials,such as size,proportion and distribution of the phases,can be controlled by adjusting the preparation process.For the amorphous and nanocrystalline alloys,the change of any elements in the alloys will lead to a great change of the microstructure.In particular,the ferromagnetic elements of Fe,Co and Ni are the key to determine whether the alloys can be obtained the desired magnetic properties by adjusting the preparation process.The addition or change of the content for the three elements will greatly influence the microstructure and magnetic properties of alloys.Therefore,the effect of composition control of the Fe,Co and Ni on structure and magnetic properties has become the research focus of amorphous and nanocrystalline alloys.In this work,the effect of composition control of Fe,Ni and Co on microstructure,thermal behavior,phase transition and magnetic properties for Fe-Ni-Co-B-Si-Cu-Zr amorphous and nanocrystalline alloys system was systematically studied,and the interrelation of the composition,structure and magnetic properties for the alloys was analyzed.It will provide a scientific basis for the research and development of amorphous and nanocrystalline magnetic materials.Firstly,the(Fe_xNi_yCo_z)₈₀B₁₀Si₂Cu₁Zr₇(x+y+z=1)alloys were prepared by melt-spinning technique.By investigating the microstructure of the as-spun alloys,it was found that the alloys in this system show a good glass forming ability.The thermal behavior and crystalline phases of the alloys were investigated,and the pseudoternary diagrams of the(Fe_xNi_yCo_z)₈₀B₁₀Si₂Cu₁Zr₇ alloys on characteristic temperatures and crystalline phases were constructed.The results show that,the crystallization process of the alloys changes from two-step to one-step crystallization with the increasing Ni content.The crystallization process of some Ni-rich alloys is one-step crystallization,which means that the multiple crystalline phases simultaneously precipitated in one crystallization process.For other alloys,the crystallization process is two-step crystallization,including primary and secondary crystallizations.The primary crystallization corresponds to the precipitation of bcc-(Fe,Ni,Co)and/or fcc-(Ni,Fe,Co)phases,and the primary crystallization temperature(T_x1)significantly increases with the increasing Fe content,making Fe-rich amorphous alloys possess a good thermal stability.The secondary crystallization temperature(T_x2)increases with the increasing Fe and Co content,which makes the residual amorphous matrix of the Fe-rich and Co-rich alloys after primary crystallization shows a good thermal stability.In addition,the Fe-rich and Co-rich alloys show a larger temperature range between T_x1 and T_x2than 172?,which is not only beneficial for the alloys to precipitate only the primary crystalline phases in a larger temperature range,but also can prevent the secondary crystallization.Secondly,magnetic properties of the as-spun and annealed(Fe_xNi_yCo_z)₈₀B₁₀Si₂Cu₁Zr₇(x+y+z=1)alloys with different ratios of Fe,Ni and Co were investigated,and the pseudoternary diagrams of(Fe_xNi_yCo_z)₈₀B₁₀Si₂Cu₁Zr₇ alloys on saturation magnetization(M_s)and coercivity(H_c)were constructed.For the as-spun alloys,their H_cshows a lower value than 45 A/m owning to the amorphous structure,and the Fe-rich and Co-rich alloys show a ferromagnetic state,whereas magnetic state of Ni-rich alloys changes from ferromagnetic state to paramagnetic state,and then shows a diamagnetic state with the increasing Ni content.For the annealed alloys,the ferromagnetic exchange coupling was enhanced owning to the precipitation of nanocrystals,making the alloys in the whole range of composition show a ferromagnetic state.It is also due to the difference of the nanocrystals in structure,size and magnetic anisotropy,causing the H_c of the alloys changes greatly with the ratios of Fe,Ni and Co.In addition,it was found that M_s shows a significantly larger increase with increasing Fe content,and(Co+Ni):Fe=3:7 is the optimal composition for the maximum M_s when y is a value in the range of 0?0.2.Moreover,Fe-rich alloys exhibit good soft magnetic properties.Thirdly,the mechanism of coercivity for(Ni_0.5Fe_0.5-zCo_z)₈₀B₁₀Si₂Cu₁Zr₇alloys in the(Fe_xNi_yCo_z)₈₀B₁₀Si₂Cu₁Zr₇alloys system was investigated.The results show that,magnetocrystalline anisotropy disappeared owing to the amorphous structure of the as-spun alloys,which makes the H_c of the alloys keeps in range of 5?14 A/m.However,nanocrystals precipitated in the annealed alloys,and the increase of Co content not only changed the magnetocrystalline anisotropy and grain size of nanocrystals,but also caused a lattice distortion in some of the alloys,which makes the H_c of the alloys changes dramatically in the range of 40?1529 A/m with the increasing Co content.Especially for the alloys with z=0.2and z=0.3,serious lattice distortion is the dominant factor for their higher H_c value than 1000A/m.Lastly,the(Fe_0.7Ni_0.1Co_0.2)_80+xB_10-xSi₂Cu₁Zr₇alloys were prepared by melt-spinning technique,and the effect of increasing Fe,Ni and Co content(decreasing B content)on microstructure,thermal behavior and soft magnetic properties of the alloys was investigated.It was found that the as-spun alloys maintain an amorphous structure in the range of x=0?8.The increasing Fe,Ni and Co content(decreasing B content)not only promoted the precipitation of primary crystalline bcc-Fe(Ni,Co)phases,but also reduced the secondary crystallization.As a result,the primary crystallization temperature(T_x1)gradually decreases,whereas the secondary crystallization temperature(T_x2)generally increases,causing the temperature range between T_x1 and T_x2 increases from 191? to 247?.It is benefit to the precipitation of a single and stable bcc-Fe(Ni,Co)phase,making the alloys maintain good soft magnetic properties in a larger temperature range.Especially for the alloys with x=7 and x=8,only bcc-Fe(Ni,Co)phases precipitated in the alloys after annealing at a higher temperature for a long time,making the alloys keep good soft magnetic properties at a higher temperature for a long time.