Preparation And Properties Of Soft Magnetic Co-based Co-Fe-B-P-C Bulk Metallic Glasses

Co-based amorphous alloy has excellent soft magnetic properties such as low coercivity,low iron loss and high permeability under high frequency application conditions,which greatly meets the demand of modern power electronic devices for energy saving and high frequency development,and thus has attracted great attention.However,due to its relatively low glass forming ability（GFA）,Co-based amorphous alloys cannot meet the requirements of some soft magnetic materials for shape and size,which limits their application.Using the viscous flow characteristics of bulk amorphous（BMGs）in the supercooled liquid region（ΔT_x）,not only the size limitation can be broken through by hot pressing or spark plasma sintering,but also the high-performance components can be batch processed by superplastic processing technology.At present,the saturation magnetic induction（B_s）of Co-based BMGs with largeΔT_x and high GFA that meet the superplastic processing technology is low due to the large addition of pre-transition metals and rare earth elements.The low B_s is not conducive to the development of miniaturization of components.Therefore,it is very important to develop Co-based BMGs with largeΔT_x,high GFA and high B_s.In order to develop Co-based BMGs with the above properties,in this paper,the alloying method was adopted,and the Co₇₅B₁₀P_7.5C_7.5 alloy with excellent soft magnetic properties was used as the basic component.The strong magnetic element Fe was added to increase the alloy B_s and improve theΔT_x and GFA of the alloy.By adjusting the content of metalloid elements to optimize the composition,the Co-based bulk amorphous alloy with largeΔT_x and high B_s was successfully prepared.On this basis,the GFA andΔT_x of the alloy are further expanded by adding Mo element.In this paper,the effects of alloy element content on the thermal stability,GFA,magnetic properties and mechanical properties of the Co-Fe-B-P-C alloy were investigated,and the supercooled liquid stability of the amorphous alloy and the GFA enhancement mechanism were discussed.The results are as follows:（1）The replacement of Co in Co₇₅B₁₀P_7.5C_7.5 alloy with Fe effectively improves the stability of undercooled liquid and GFA.In the Co_75-xFe_xB₁₀P_7.5C_7.5（x=0–35）alloy,obvious glass transition occurs when x=10,and theΔT_x of the alloy increases to 47 K with the increase of x.When x≥20 alloy can be prepared amorphous bar,and when x≥30 alloy GFA maximum,（critical diameter）dc can reach 1.2 mm.（2）By investigating the crystallization behavior of the alloy at elevated temperature,Fe addition changed the crystallization behavior of Co_75-xFe_xB₁₀P_7.5C_7.5（x=0–35）amorphous alloy.When x=0,the initial crystallization phase of the alloy was fcc-Co phase.With the increase of Fe content,the initial crystallization phase gradually changed into B₂CCo₁₁ phase and Fe₂₃（B,C）₆+Co Fe+Fe₃B mixed phase.The complication of the initial crystallization phase was beneficial to improve the stability of the supercooled liquid of the alloy.（3）Co_75-xFe_xB₁₀P_7.5C_7.5（x=20–35）BMGs have excellent soft magnetic properties,and their B_s and H_c are 1.04–1.21 T and 2.9–7.2 A/m,respectively.This series of alloys also showed good mechanical properties,with yield strength（σ_y）and plastic strain（ε_p）between3243–3665 MPa and 0.1%–2.1%,respectively.In addition,the minimum viscosity of the amorphous alloy withΔT_x more than 40 K can reach 3×10⁹ Pa·s,and its low viscosity,largeΔT_x and S value show that the alloy has good superplastic processing potential.（4）For Co₄₅Fe₃₀（B,P,C）₂₅ alloys,bulk amorphous can be prepared in the composition region of B content of 5%-10%,P content of 7.5%-10%,C content of 7.5%-10%,andΔT_xis more than 40 K.TheΔT_x,T_rg,γvalues of this series of amorphous alloys have good correspondence with the change trend of d_c with composition,that is,the amorphous alloys with larger GFA have better thermal stability.（5）For Co_45-xFe₃₀B₁₀P_7.5C_7.5Mo_x（x=0–6）alloys,the addition of Mo improves the stability of supercooled liquid and increases the GFA of the alloy.TheΔT_x and d_c of x=4 alloy reach 63 K and 2.0 mm,respectively.At the same time,with the increase of Mo content,theσ_yand H_v of the alloy increased gradually,and the B_s,H_c,andε_p decreased gradually.Among them,the B_s,H_c,σ_y,ε_p and H_v of Co₄₁Fe₃₀B₁₀P_7.5C_7.5Mo₄ alloy were 0.91 T,1.7 A/m,3769MPa,1.3%and 795,respectively.