Synthesis And Properties Of Co-based (Co,Fe)–(La,Y)–B Bulk Metallic Glasses

Co-based metallic glasses have comprehensive soft magnetic properties including high permeability,low coercivity(H_c),low core loss and magnetostrictive coefficient,especially the excellent high-frequency soft magnetic properties,which exhibit a good promise for applications in the field of electronics and communication technology.However,the glass-forming ability(GFA)of Co-based metallic glasses is poor which limits the applications.Considering the advantage of superplasticity in the supercooled liquid region(?T_x)of the BMGs,not only large-sized BMG materials but also mass production of micro-magnetic components can be obtained.However,the metallic glass which is suitable for the superplastic forming processes should have a wide?T_x and a high GFA.At present,the reported Co-based BMGs with large?T_x contain a quantity of early transition metals(ETM),which results in a severely decrease in the saturation magnetic flux density(B_s).Therefore,it is of great significance to develop the Co-based BMGs with high B_s and large?T_x.In this work,the effects of Y and La contents on the thermal stability,GFA and magnetic properties of Co₇₅B₂₅ metallic glass have been investigated,and the thermal stability and magnetic properties of Co_71.5RE_3.5B₂₅metallic glass with different rare earth elements(RE)were investigated.Subsequent substitution of Co by Fe and La by Y on the thermal stability,GFA and magnetic properties of Co-RE-B(RE=La,Y)and Co-Fe-La-B alloys were investigated,respectively.The relationship among the composition with magnetic properties and GFA of alloys was also discussed.The main findings are as follows:1.For the Co-RE-B metallic glasses,except for the light rare earth elements(LRE)La and Pr alloys,which have no glass transition phenomenon,the other alloys have obvious?T_x,and the heavy rare earth elements(HRE)alloys have larger undercooled liquid stability,the?T_xof which is between 25 K-33 K.In addition,the Co-HRE-B alloys also have larger GFA,and the critical thickness(t_c)of Co_71.5Y_3.5B₂₅ and Co_71.5La_3.5B₂₅ metallic glass is 240?m and 50?m,respectively.2.With the increase of RE content,the B_s of Co_75-xRE_xB₂₅(RE=La,Y)alloys decreases gradually,and the H_c decreases first and then increases,reaches to the minimum when x=3.5.For Co_71.5RE_3.5B₂₅ metallic glasses,the B_s of alloys containing different RE is similar,but the alloys containing HRE have lower H_c,below 3.0 A/m.3.Substitution of Co by Fe in Co-RE-B metallic glasses can significantly improve the stability and GFA of supercooled liquid.With the increase of Fe content,the?T_x of(Co_1-yFe_y)_71.5RE_3.5B₂₅(RE=La,Y)alloy gradually increases from 0 and 33 K to 34 K and 64 K,respectively.The BMGs can be produced in(Co_1-yFe_y)_75-xY_xB₂₅(y=0.2-0.5,x=3-5)alloys,within the?T_x and critical diameter(d_c)of(Co_0.7Fe_0.3)₇₁Y₄B₂₅ are 51 K and 1.5 mm,respectively.4.With the increase of Fe content,the B_s and H_c of(Co_1-yFe_y)_71.5RE_3.5B₂₅(RE=La,Y)metallic glasses tend to increase gradually.With the increase of Y content,the B_s of(Co_0.7Fe_0.3)_75-xY_xB₂₅ alloys gradually decreases,while the H_c decreases first and then increases.Among them,the(Co_0.7Fe_0.3)_71.5Y_3.5B₂₅ alloy has the lowest H_c,and the B_s reaches to 1.0 T.Co-Fe-Y-B BMGs also have good mechanical properties,which the compressive yield strength(?_c,y)ranges from 3793 to 4152 MPa and the plastic deformation(?_c,p)can reach to0.9%,the Vickers hardness(H_v)ranges from 1072 to 1336.5.For the(Co_0.7Fe_0.3)_71.5La_3.5-xY_xB₂₅(x=0-3.5)metallic glasses,with the x increases from0 to 3.5,the?T_x increases gradually from 29 K to 50 K,and the GFA also increases gradually.With the increase of Y content,the B_s has little change,while the H_c gradually decreased from7.5 A/m to 5.4 A/m.