Microstructure And Properties Of FeCoCrNiMnN_x High-entropy Alloys Prepared By Powder Metallurgy

FeCoCrNiMn high-entropy alloy(HEA)has a simple crystal structure and good plasticity and toughness,but existing relatively low strength,then added with N element in order to improve the strength.The alloy prepared by the powder metallurgy has many advantages,such as fine grains,uniform composition and high utilization of raw materials,therefore FeCoCrNiMnNx(x=0,0.1,0.2,0.3,mol)HEAs were prepared by this method in this paper.Effects of N addition on microstructure and mechanical properties of FeCoCrNiMn HEA were investigated by X-ray diffraction,scanning electron microscope,transmission electron microscope,universal material testing machine and electrochemical workstation etc.The results show:During the mechanical alloying process of FeCoCrNiMnNx HEAs,the alloying elements were gradually alloyed and formed as face-center(FCC)solid solutions within 45h of milling.After the vacuum hot pressing sintering(VHPS),the microstructure of alloys were basically the same,which contained FCC matrix phases with traces of M23C6carbides(M=Cr,Fe,Co),a phases and Cr2N phases.Meanwhile,it also found some nano twins.Sintering temperature has an important effect on the microstructure and mechanical properties of FeCoCrNiMn HEA.In the temperature range(900??1000?)sintering,the alloys have been fully sintered,and its microstructure show that the bulk light areas with low Cr content are FCC phases as a matrix,while the irregular dark areas with high Cr content are precipitations.As the sintering temperature increased,the hardness of the alloys first increased and then decreased,accompanied by a gradual increase in plasticity.From the considerations of comprehensive mechanical performance,the optimum sintering temperature of this alloy is 900?.N element has a significant strengthening effect on FeCoCrNiMn HEA.As N content of the alloys increased,the yield strength,compressive strength and hardness gradually increased,accompanied by a decrease in plasticity,and the wear resistance also gradually increased,where the wear mechanism was slight flaking wear and abrasive wear.Adding N element is helpful to improve the high temperature oxidation resistance of FeCoCrNiMn HEA.The oxidation rate of the alloys decreased with the increase of N content;At800'C,the surface oxide layer of the alloys mainly consisted of Mn3O4 and a small amount of MnCr2O4;At 900?,the surface oxide layer of the alloys were dominated by Mn3O4;At 1000?,the surface oxide layer of the alloys occurred flaking,and there are also the other oxides such as CrO and Cr2O3 in addition to Mn3O4,MnCr2O4.In 3.5w.t%NaCl solution,FeCoCrNiMnN0.2HEA has the smallest corrosion current density;In 3.5w.t%NaOH solution,FeCoCrNiMnN0.3 HEA has the smallest corrosion current density;In 1 mol/L H2SO4 solution,the corrosion potential of the alloys first increased and then decreased with the increase of N content,FeCoCrNiMnN0.1 HEA has the smallest corrosion current density,which exhibits the best corrosion resistance.