Preparation And Properties Of FeCoNi Based High Entropy Amorphous Soft Magnetic Alloys

High entropy alloys（HEAs）are multi-component new alloys,and the multiple principal elements in equal or near equal atomic percent（at.%）ranging from 5 to 35.Due to its unique compositional rules,the microstructure and excellent mechanical properties have received extensive attention in the field of advanced metal materials.Scholars have payed attention to the mechanical properties of high-entropy alloys.It is worth noting that most of the previous researches are focused on its mechanical properties rather than the magnetic properties.Considering that the high raw material cost and bad temperature stability of high-entropy alloy,it is hard to generalize the use of high-entropy alloy.In order to realize the commercial application of high-entropy alloy,it is necessary to increase the service life and improve the comprehensive properties of high-entropy alloys.In view of the above problems,the thermodynamic properties,corrosion resistance and magnetic properties of Fe₂₄Co₂₄Ni₂₄Si₁₃B₉M₆,Fe₂₇Co₂₇Ni₂₇Si₉B₉RE₁ and Fe₂₇Co₂₇Ni₂₇Si_10-xB₉La_x alloys were investigated in this work.In the meantime,the mechanical properties of Fe₂₇Co₂₇Ni₂₇Si_10-xB₉La_x high-entropy alloys were investigated.（1）The effects of alloying elements Cr,Mo,Nb and V on its structure,thermodynamic properties,corrosion resistance and magnetic properties of six-element Fe₂₄Co₂₄Ni₂₄Si₁₃B₉M₆high-energy amorphous soft magnetic alloys are studied.According to the results of experiments,the alloy presents a completely amorphous structure with an entrainment speed of45 m/s.The addition of metal elements Cr,Mo,Nb and V can effectively improve the thermal stability and amorphous forming ability of the high entropy alloys.There is a significant enhancement in the amorphous forming ability of the alloy with the addition of Nb in high entropy alloys,and its T_rg reached 0.636.The addition of Mo lead to a greatest influence on the primary crystallization temperature(T_x1)and the secondary crystallization temperature(T_x2)of the alloy,and its T_x2 had reached 631°C.Treated high entropy alloys with 0.1 mol/L NaCl solution,the self-corrosion voltage and corrosion current density of alloy with Cr is-0.27 V and1.25×10^-66 A/cm² respectively,which has the best corrosion resistance.The high entropy alloys with V has the lowest saturation magnetic induction（B_s）,Mo alloy has a maximum T_c of 250°C,and the ordinary Co-based amorphous alloy has a curie temperature（T_c）of 200°C.In the dynamic M-T curve of V-based alloy,two T_c existed.The one is at the amorphous phase’s T_c and the other is the T_c of the crystallization phase.The T_c of the crystal phase of the Cr-based alloy exceeds 700°C and the T_c of the ordinary Fe-based amorphous nanocrystalline alloy is range from 550°C to 600°C.The ultra-high T_c of the crystallization phase provides an experimental basis for Fe₂₄Co₂₄Ni₂₄Si₁₃B₉M₆ series alloy working in high temperature environment.（2）In the Fe₂₇Co₂₇Ni₂₇ Si₉B₉RE₁ alloys,the addition of rare earth element lead to a slightly increase in the T_x1 and a great increase on the T_x2 of the alloys.Compared with the alloys with rare earth-free element,the addition of rare earth Nd lead to T_x2 reach 547°C with an increasement of 30°C.In terms of corrosion resistance,the addition of rare earth element Pr significantly improve the corrosion resistance of the alloys,while adding rare earth Nd can deteriorate the corrosion resistance of the alloys.In basis on the study on the magnetic properties of the alloy,adding rare earth element La can slightly reduce the coercivity of the alloys.The heat treatment is beneficial to increase the B_s.When the temperature of heat treatment is near the crystallization temperature,the B_s of the alloys increased in a certain extent,but the other soft magnetic properties of the alloy deteriorated significantly.（3）Preparing Fe₂₇Co₂₇Ni₂₇Si_10-xB₉La_x alloys by replacing some amount of non-metallic elements Si with rare earth La,it is found that adding a small amount of rare earth element La can inhibit the growth of alloy crystal grains and the precipitation of intermetallic compounds.The thermodynamic study of the alloy shows that the relationship between the T_x1,T_x2 and the rare earth.When the content of rare earth La is 0.51 at.%,the high entropy alloys have a maximum T_x1 of 424°C,and the maximum T_x2 of 549°C occurred with the La content of 0.87at.%.The B_s of Fe₂₇Co₂₇Ni₂₇Si_9.4B₉La_0.6 alloy reaches to 1.25 T with high temperature annealing of 580°C for 5 minutes.In addition to the addition of trace rare earth can also improve the fracture strength and toughness of as-cast alloys.