Formation,Nanocrystalline Regulation And Magnetism Of New Manganese-Based Amorphous Alloys

Amorphous alloys are a new type of metal materials that lack the periodic arrangement of atoms in crystalline materials,long-range disordered atomic structures,and no grain boundaries.The alloys usually exhibit unique and excellent physical and chemical properties.Moreover,the nanocrystalline/amorphous alloys formed from amorphous precursors often show new properties and functions due to the effect of heterostructures and nano-effects.In recent years,many amorphous alloy systems have been developed by researchers,showing unique properties and potential applications in the field of materials science.Mn is a transition metal element with exotic structure and magnetism,the Mn-based alloys have more various magnetic structures and exhibit peculiar magnetic phenomenon.However,researching on manganese（Mn）-based amorphous alloys is rarely reported among these alloys.In view of the current demand for the development and application of new metastable amorphous/nanocrystalline alloys in China,the present work would like to develop new Mn-based amorphous alloy ribbons and investigate the alloys’crystallization behaviors and formed nanocrystalline phases and magnetic properties,exploring the possible special properties in the new Mn-based amorphous/nanocrystalline alloys.A series of novel manganese-based Mn-Si-B,Mn-Si-B-（Cu,Ag）-（Nb,Mo）,Mn-Fe-Si-B-EM,Mn-Cr-Fe-Si-B-Zr amorphous alloys were produced by the copper roller melt spinning technique.The phase evolution behaviors and formed nanocrystalline phases of the amorphous alloys were studied by crystallized annealing.Besides,we also conducted magnetic characterization for the Mn-based amorphous nanocrystalline alloy to reveal their magnetic transition behaviors.The researching contents and conclusions are as follows:（1）Considering amorphous formation and the various exotic magnetic properties among silicide,Si and B were chosen to introduce Mn-Si-B alloy system to develop new Mn-based amorphous alloys.The Mn_balSi_10~27B_7~10compositions can achieve amorphous structure by melt spinning method.In the Mn-Si-B amorphous alloy system,Si composition has a great influence on the crystallization behavior and the formed phases upon annealing.When the Si content is 10～15 at.%,the Mn_balSi_10~15B_7~10 amorphous alloys show one-stage crystallization behavior,simultaneously formedα-Mn（Si）,Mn6Si,and Mn₂B after crystallized annealing;when Si is 20 at.%,the amorphous alloy shows one-stage crystallization,formedα-Mn（Si）,Mn₃Si,and Mn₂B after annealing.When Si is 25 at.%,the alloy shows two-stage crystallization,T_x1and T_x2are 538℃and 596℃,respectively,corresponding to the formation of Mn₅Si₃and Mn₂B.（2）In Mn-Si-B-（Cu,Ag）-（Nb,Zr,Mo）alloy system,the Mn₇₄Si₁₃B₉Cu₁M₃（M=Zr,Nb,Mo）amorphous alloys show one-stage crystallization,formed multi-phases ofa-Mn（Si）,Mn₆Si,Mn₉Si₂ and Mn₂B upon annealing.The Mn₆₄Si₂₅B₇M₁Nb₃（M=Cu,Ag）amorphous alloys exhibit three-stage crystallization events,which form Mn₅Si₃,Mn₃Si and boride,respectively.The crystallization phase transformation of Mn₆₄Si₂₅B₇M₁Nb₃（M=Cu,Ag）amorphous alloys can be expressed as:Amorphous（Amor.）→Mn₅Si₃+Amor.→Mn₅Si₃+Mn₃Si+Amor.→Mn₅Si₃+Mn₆Si+Mn₂B.（3）In Mn-Fe-Si-B-EM（EM=Zr,Nb,V）alloy system,Mn₅₅Fe₁₅Si₂₀B₇EM₃（EM=Zr,Nb,V）amorphous alloys exhibit two-stage crystallization,T_x1 precipitatesa-Mn and Mn-Si phases,T_x2is Mn₂B.For EM=Zr,Nb,the phase evolution during annealing crystallization is expressed as:Amor.→α-Mn+Amor.→α-Mn+Mn₆Si+Amor.→α-Mn+Mn₆Si+Mn₃Si+Amor.→α-Mn+Mn₆Si+Mn₃Si+Mn₂B;for EM=V alloys,it is expressed as:Amor.→α-Mn+Mn₃Si+Amor.→α-Mn+Mn₃Si+Mn₆Si+Amor.→α-Mn+Mn₆Si+Mn₃Si+Mn₂B.For the tuning Si/B ratio Mn₅₅Fe_35-xSi_xB₇Zr₃（x=10,13,15,17,20,22,25）alloys,x=15～25at.%,the alloys are completely amorphous state sample with two-stage crystallization,T_x1 is600℃～650℃,T_x2 is 670℃～720℃.After annealed at around T_x1,Mn₅₅Fe_35-xSi_xB₇Zr₃（x=10,13,15,17,20,22,25）formed one or several phases ofα-Mn,Mn Si _X（R ornphase）,Mn₃Si and Mn₅Si₃;for x=17,mainly precipitated Mn₃Si,for x=22,formed single Mn₅Si₃ phase.（4）Mn₃₀Cr₂₀Fe₂₀Si₂₀B₇Zr₃（HEA-1#）and Mn₂₅Cr₂₅Fe₂₅Si₁₅B₇Zr₃（HEA-2#）amorphous alloys exhibit two-stage crystallization,T_x1 of them are 663℃and 652℃,respectively,showing good thermal stability.After annealed at 600℃～730℃,the formed phase evolution behavior of HEA-1#is expressed as:Amor.→fcc+Mn Si_x+Amor.→bcc+Mn Si_x+Amor.→bcc+Mn Si_x+M₂B;HEA-2#is expressed as:Amor.→fcc+Amor.→fcc+Mn Si_x.（5）The Mn-Si-B amorphous alloy has spin glass transition behavior,and the spin glass transition temperature（T_f）is 22～23K.With the increase of Si/B,the magnetization（M）of Mn₇₈Si_22-xB_x（x=7,8,9）amorphous alloys increases around T_f,meanwhile the maximum peak broadens,indicating the alloys have more obvious spin glass transition characteristics.The Mn_93-xSi_xB₇（x=15,20,25）amorphous alloys also exhibit increasingly spin-glass behavior with increasing Si/Mn.Below T_f,it is difficult for Mn-based amorphous alloys containing spin-glass phases to magnetize to saturation.（6）For Mn-Si-B-（Cu,Nb）,Mn-Fe-Si-B-EM（EM=Zr,Nb,V）,multi-metal components Mn-Cr-Fe-Si-B-Zr,the magnetic transformation analysis of amorphous nanocrystalline alloys shows that the alloys in the amorphous state gradually transfer from the spin glass phase（SG）state to the paramagnetic state（PM）with the increase of temperature,and the magnetic phase transition can be expressed as:SG→PM;for the nanocrystalline/amorphous composite structure samples with one or two nanocrystalline phases of Mn₅Si₃,Mn₅Si₃+Mn₃Si,a-Mn+Mn₃Si,a-Mn+Mn₃S,fcc+Mn Si_x formed by annealing,in which the magnetic transition behavior has undergone a fundamental change,from the SG state to the ferromagnetic（FM）state through the spin glass transition,and then into the PM state after maintaining the FM state in a wide temperature range,and its magnetic phase transition:SG→FM→PM.（7）The MFM magnetic domain structure analysis at room temperature shows that the magnetic domain structure distribution on the surface of the Mn₅₅Fe₁₅Si₂₀B₇Zr₃ alloy ribbons in the amorphous state is disordered without a specific shape,while the magnetic domain structure of the annealed nanocrystalline alloy is thin and uniform with no specific shape.The distribution of magnetic domains of Mn₂₅Cr₂₅Fe₂₅Si₁₅B₇Zr₃ nanocrystalline alloy has a spherical cluster-like magnetic domain structure,and the magnetic moments in the center and surrounding are opposite.