Composition Design,microstructure And Properties Of Fe_xNiCo(Al/Si)_y High Entropy Alloys

In recent years,the microstructure and mechanical properties have been studied extensively.However,the function properties have not been explored extensively.Soft magnetic high-entropy alloys(HEAs)were designed through reasonable element selection,composition design and annealing process optimization in order to balance the soft magnetic and mechanical properties.These HEAs ensure that it wiil not fail in extreme service conditions.In this paper,the Al and Si were added into to the single-phase FCC structure Fe Ni Co matrix alloy,and Al or Si were added into to the dual-phase FCC+PC structure Fe₂Ni Co matrix alloy.There sereies of alloys with a excellent combination of strength-plasticity and soft magnetic properties were designed.A total of 17 as-cast HEAs are:(Fe_1/3Ni_1/3Co_1/3)_100-x(Al_1/4Si_3/4)_x,Fe₂Ni Co Si_x,Fe₂Ni Co(Al Si)_x.The as-cast(Fe_1/3Ni_1/3Co_1/3)₈₅(Al_1/4Si_3/4)₁₅ and Fe₂Ni Co(Al Si)_0.4 have been showed excellent comprehensive performance.They were annealed at 600?and 800?respectively in order to improve their performance.The microstructure morphology,crystal structure,mechanical properties,magnetic properties and thermal expansion properties were analyzed in this paper,the main findings are as follows:With the increase of Al and Si,the structure of(Fe_1/3Ni_1/3Co_1/3)_100-x(Al_1/4Si_3/4)_x HEAs gradually changed from FCC phase to FCC+BCC phase;the structure of Fe₂Ni Co Si_x HEAs changed from FCC+PC phase to FCC+BCC phase;while the Fe₂Ni Co(Al Si)_x HEAs transformed from FCC+PC structure to FCC+BCC structure,and finally a single-phase BCC structure.In these series of alloys,element segregation was observed and the microstructure showed typical coarse dendritic.These HEAs have high saturation magnetization and low coercivity,showing excellent soft magnetic properties.With the increase of Al and Si elements,the yield strength of(Fe_1/3Ni_1/3Co_1/3)_100-x(Al_1/4Si_3/4)_xand Fe₂Ni Co Si_xHEAs increased significantly,and the plasticity decreased,but they did not show a linear change.The saturation magnetization and resistivity of two series of alloys showed a downward trend,but the coercivity of the Fe₂Ni Co Si_xHEAs gradually declined,while the other series of alloys showed an increasing trend.However,the yield strength of Fe₂Ni Co(Al Si)_x HEAs increased almost linearly and the plasticity decreased;the values of saturation magnetization decreased linearly,the electrical resistivity increased linarly and the values of coercivity fluctuate.In the same temperature range and heating rate,when the alloy is FCC+BCC dual-phase solid solution alloy,the thermal expansion coefficient shows a positive correlation,which is lower than that of BCC single-phase solid solution alloy.The Fe₂Ni Co(Al Si)_0.4 HEA showed excellent comprehensive performance.After annealing at 600?and 800?,(Fe_1/3Ni_1/3Co_1/3)₈₅(Al_1/4Si_3/4)₁₅and Fe₂Ni Co(Al Si)_0.4HEAs have not undergone significant phase transformation,and their compressive yield strength significantly improved,while plasticity decreased.After the heat treatment,The(Fe_1/3Ni_1/3Co_1/3)₈₅(Al_1/4Si_3/4)₁₅HEA was annealed at 800?,fine needle-like phases or dot-like phases appeared at this temperature.The saturation magnetization and resistivity increased significantly,and the coercivity decreased slightly,showing a certain overall performance improvement.The Fe₂Ni Co(Al Si)_0.4HEA exhibits the oppsite soft magnetic properties of the above alloys,which shows a deteriorating tendency of overall performance.