Structural Regulation And Soft Magnetic Properties Of Fe-Co-Ni-Al-(Si,Mn,Ga)high Entropy Alloys

As a hot research direction in recent years,high-entropy alloys（HEAs）have many excellent properties when compared with traditional alloys.The mechanical properties such as hardness,compression,tension,serration behavior,fatigue and nanoindentation of HEAs have been well studied.In addition,the HEAs also have such excellent functional properties as electrical properties（including superconductivity）,magnetic properties,electrochemical properties and hydrogen storage properties,etc.,showing a broad application prospect.Compared with the most widely used soft magnetic material silicon steel,the soft magnetic high entropy alloy has high resistivity,which can reduce the energy loss in transformers.Compared with amorphous and nanocrystalline soft magnetic materials,high-entropy soft magnetic alloys are easier to manufacture,and the range of composition and magnetic parameters is more adjustable.Higher resistivity makes magnetic high entropy alloys more attractive when manufacturing high frequency magnetic devices.However,the performance parameters of high-entropy soft magnetic alloys need to be further optimized because the coercivity of the currently studied soft magnetic high-entropy alloys are still relatively high,about 100～30000 A/m,compared with conventional silicon steels.Moreover,the high frequency behavior of soft magnetic high entropy alloys is largely unknown.In this study,we have prepared five-element high-entropy alloys with several different systems based on CoFeNi ternary alloys adding Al、Si、Mn and Ga elements by melting and casting.Adding nonmagnetic elements to the CoFeNi ternary alloy will reduce the saturation magnetic induction of the alloy.By adjusting the composition,the obtained microstructure and its effect on magnetic properties were studied.The saturation magnetic induction of high-entropy soft magnetic alloys in CoFeNiAlSi system is high whereas the coercivity is low.Among them,(Co₃₀Fe₄₅Ni₂₅)_0.8(Al₄₀Si₆₀)_0.2 HEA has a single-phased body center cubic（BCC）structure,and the compressive yield strength is1636 MPa.The high-entropy soft magnetic alloy also has a good combination of electrical and magnetic properties:resistivity（R）is 68.0μΩ·cm,saturation induction strength（B_m）is1.24 Tesla,coercivity（H_c）is 59.7 A/m.In addition,to studying the static magnetic properties of high entropy alloys,the relationship between saturation magnetic induction,operating frequency and total power loss of high entropy alloys is also studied to understand the contribution of static hysteresis loss,classical eddy current loss and excessive eddy current loss to total power loss.The results show that the power loss of(Co₃₀Fe₄₅Ni₂₅)_0.8(Al₄₀Si₆₀)_0.2 HEA is better than that of Fe-Si alloy containing 3 wt%Si at operating frequency above 200 Hz,the total power loss of x=0 alloy is the lowest when the frequency is less than 150 Hz,the total power loss of x=0.2 alloy is the lowest when the frequency is between 150 and 1000 Hz.When the frequency is greater than 1000 Hz,x=0.15 alloy exhibits minimal energy loss,which is mainly due to the combination of static hysteresis loss,classical eddy current loss and excessive eddy current loss.