Microstructure And Properties Of AlCrMnFeNiCu_x High-entropy Alloys

As a new type of alloy,high entropy alloy has attracted much attention.It has great advantages in strength,hardness,wear resistance,corrosion resistance,high temperature oxidation resistance and other aspects,and has great application potential in turbine blades,nuclear fusion reactor and marine equipment.Based on the excellent properties of high-entropy alloy,AlCrMnFeNiCu_x（x=1.0,0.8,0.6）high-entropy alloys were prepared by vacuum arc melting technology.The effects of Cu content and annealing temperature on microstructure evolution,mechanical properties,friction and wear and corrosion resistance of high-entropy alloy were studied,respectively.The main results are as follows:In terms of microstructure evolution,the microstructure of AlCrMnFeNiCu_xhigh-entropy alloys after annealing at different temperatures were studied by XRD,SEM,EDS and TEM.It is found that the alloys after annealing are composed of two different BCC structures（Fe-Cr phase and Al-Ni phase）and one FCC structure（Cu-rich phase）,which are reflected in the morphology of dendritic region and interdendritic region.With the increase of annealing temperature,amplitude-modulated decomposition takes place first and then spinodal decomposition diffusion takes place.After annealing at the high temperature,Cu-rich phase is precipitated in the dendrite region as nanoscale precipitated phase.In terms of mechanical properties and friction and wear behavior,the hardness of AlCrMnFeNiCu_xhigh-entropy alloys increase first and then decreases with the increase of annealing temperature.With the decrease of Cu content,the hardness of Al Cr Mn Fe Ni Cu_0.6alloy increases slightly.Among them,Al Cr Mn Fe Ni Cu_0.6alloy after 400°C annealing for 4h,the results show that BCC volume fraction phase increases,FCC phase volume fraction decreases,and the hardness reaches the highest 486 HV.After annealing at 1000°C for 4 h,the nanoscale Cu-rich precipitates on the dendrite and hinders dislocation movement,leading to the improvement of the compressive strength and ductility of the alloy.The friction and wear results show that annealing temperature has little effect on the dry friction coefficient of the alloy,but with the increase of annealing temperature,the wear resistance of the alloy decreases.Al Cr Mn Fe Ni Cu_0.6alloy annealed at 400°C has the best wear resistance,with the wear rate of 1.1×10^-3mm³·N^-1·m^-1.The wear mechanisms are abrasive wear,adhesive wear and oxidation wear.In terms of corrosion resistance,AlCrMnFeNiCu_xhigh-entropy alloy in 3.5 wt.%Na Cl solution,Cl^-is easily adsorbed on the surface of the passivation film,and accumulates in the Cu-rich region to damage the passivation film.The corrosion types of the alloy surface are pitting corrosion and electrocouple corrosion.Among them,the three alloys show the best corrosion resistance after annealing at 400°C for 4 h.Al Cr Mn Fe Ni Cu_0.6alloy has the highest corrosion potential and the corrosion current density decreases by an order of magnitude compared with other alloys.In 0.5 mol/L H₂SO₄solution,the impedance profiles of Al Cr Mn Fe Ni Cu_0.8and Al Cr Mn Fe Ni Cu_0.6alloys annealed at 400°C and 1000°C show obvious inductive reactance arcs,indicating that the surface of Al Cr Mn Fe Ni Cu_0.8and Al Cr Mn Fe Ni Cu_0.6alloys is partially or completely active,and the pitting morphology of dendrite region appears under inductance.In addition,the uneven phase distribution in the alloy leads to galvanic corrosion.In the above two corrosion systems,passivation region exists in the polarization curve.XPS results show that the main components of passivation film are Al,Cr and Ni oxides,which play the positive role in the formation of passivation film.