Effects Of Similar Element Substitution On Microstructure And Magnetic Properties Of Fe-Nb-B Nanocrystalline Alloys

Under the development of low-carbon economy,power electronic equipment is developing in the direction of energy saving and miniaturization.Soft magnetic materials with high saturation magnetic induction（B_s）and low iron loss are highly desired.Fe-based nanocrystalline soft magnetic alloys have attracted extensive attention due to their excellent magnetic properties.Among them,Fe-M-B（M=Zr,Nb,Hf）（Nanoperm）nanocrystalline alloys exhibit B_s exceeding 1.5 T,and excellent comprehensive soft magnetic properties such as low coercivity（H_c）and low iron loss.It can form a fine nanocrystalline structure under low pressure,and is expected to become a candidate material for a new type of iron core to realize industrialization.However,the amorphous forming ability（AFA）of this series of alloys is poor.Insufficient AFA will lead to crystallization of the quenched precursor,abnormal grain growth during the annealing process,poor magnetic softness after nanometerization,and also increase the precursor.The brittleness of the ribbons makes it difficult to wind.Therefore,it is of great significance to develop Fe-based nanocrystalline soft magnetic alloys with both high AFA and high B_s.In this paper,the effects of similar elements P,Hf,Co replacing B,Nb,Fe on the amorphous formation ability,thermal stability,microstructure and soft magnetic properties of Fe-Nb-B alloys were investigated and studied,and the different elements were explained.The mechanism of the effect of substitution on the thermal stability of the amorphous alloys,the microstructure and soft magnetic properties of the nanocrystalline alloys.The main findings are as follows:（1）Fe_91-xNb_xB₉（x=5-8）alloy has poor AFA,and the melt-spun ribbons all have different degrees of crystallization.With the increase of Nb content from 5 to 8 at.%,the T_x1and T_x2 of the quenched alloy increased from 664 K and 975 K to 782 K and 1075 K,respectively.Nb can effectively improve the thermal stability of the amorphous phase.Increasing the Nb content can reduce the H_c of Fe_91-xNb_xB₉ nanocrystalline alloys,but at the same time reduce B_s.When the Nb content is 7 at.%,its B_s and H_c are 1.50 T and 20.0 A/m,respectively,and have good comprehensive soft magnetic properties.（2）The substitution of 2-6 at.%of P for B in Fe₈₄Nb₇B_9-xP_x（x=0-6）alloys can effectively increase AFA,and the quenched band transforms from a partially crystalline state to a fully amorphous state.With the increase of P content from 0 to 6 at.%,the T_x1 and T_x2 of the quenched alloy decreased from 774 K and 1078 K to 716 K and 955 K,respectively.The increase of P content decreased the thermal stability of the alloy.2-4 at.%of P replaces B,the D_α-Fe of Fe₈₄Nb₇B_9-xP_x nanocrystalline alloy is reduced to 11-12 nm,its V_cry is increased to 53.1-57.9%,and the H_c of the alloy is reduced to 12.8-15.3 A/m,B_s increased to 1.55-1.57 T.However,increasing the P content to 6 at.%coarsens theα-Fe grains and reduces the soft magnetic properties.（3）The melt-spun ribbons of Fe₈₄Nb_7-xHf_xB₅P₄（x=0-3.5）alloys are all fully amorphous.As the Hf content increases from 0 to 3.5 at.%,the T_x1 and T_x2 of the amorphous alloys are increased from 744 K and 1001 K to 778 K and 1028 K,respectively.An appropriate amount of Hf instead of Nb increased the thermal stability of the amorphous phase.With the increase of Hf content from 0 to 3.5 at.%,the D_α-Fe of the nanocrystalline alloys decreased from 12 to 9nm,and the V_cry decreased from 57.6%to 55.3%.An appropriate amount of Hf replaces Nb further refine the grain size of the alloy.Increasing the Hf content can reduce the H_c of this series of nanocrystalline alloys,while the B_s is slightly reduced.When the Hf content is 3.5at.%,its B_s and H_c are 1.55 T and 11.2 A/m,respectively.（4）For amorphous Fe_84-xCo_xNb_3.5Hf_3.5B₅P₄（x=0-10）alloys,as the Co content increases from 0 to 10 at.%,the T_x1 and T_x2 of this amorphous alloys was slightly reduced from 778 K and 1028 K to 770 K and 1025 K,respectively.The replacement of Fe by Co slightly reduced the thermal stability of the amorphous phase.As the Co content increased from 0 to 10 at.%,the D_α-Fe of the nanocrystalline alloys increased slightly from 9 to 11 nm,and the V_cry slightly increased from 55.3 to 56.9%.With the increase of Co content,the B_s and H_c of the nanocrystalline alloys increased from 1.55 T and 11.2 A/m to 1.64 T and 35.9 A/m,respectively.