| The high entropy alloy(HEA)breaks the ratio idea of traditional alloys,a new type of alloy is prepared by the method of equal atomic ratio or near.It has attracted a great deal of research interest and has a bright future,because of its new design concept,unique structure and excellent mechanical properties,good corrosion resistance,wear resistance and electromagnetic properties.In this paper,CoCrFeNi,CoCrFeNiWx and CoCrFeNi Mox(x=0.2,0.5)HEAs were prepared by arc melting method,the effects of pre-deformation treatment and element addition on the microstructure,morphology,composition,corrosion resistance and mechanical properties of CoCrFeNi HEAs were studied by using XRD,DSC,FESEM,microhardness tester,electrochemical workstation,and MTS universal testing machine etc.It is hoped that HEAs with excellent mechanical properties and corrosion resistance can be obtained through the new process design and the introduction of new components.The main results are as follows:1.The as cast CoCrFeNi HEA has a single FCC solid solution structure,and the micro-morphology is a typical dendritic structure.In the aspect of mechanical properties,as cast CoCrFeNi HEA shows excellent plastic deformation ability,but the yield strength and microhardness are lower,which are 167 MPa and 168.9 HV,respectively.It was found that,the CoCrFeNi HEAs with 20% and 50% of the pre-pressing shape variables still maintain a single FCC solid solution structure,while the phase structure of the alloy treated with 80% pre-pressing has been changed obviously,from a single FCC solid solution to a FeNi3 type intermetallic phase(FCC structure).Proper pre-deformation treatment can improve the electrochemical corrosion resistance of CoCrFeNi HEA in seawater,the pitting corrosion potential of the 80% pre-pressing alloys is up to 0.978 V,which is significantly higher than 0.157 V of the as cast CoCrFeNi HEA,and there are two typical passivation,which shows excellent pitting resistance.In addition,proper pre-deformation treatment can improve the mechanical properties of as cast CoCrFeNi HEA,the yield strength of thealloys with 20% and 50% pre-pressing treatment respectively up to 544 MPa and 784 MPa,which are significantly higher than that of as cast CoCrFeNi HEA,and increased by 233% and 380%,respectively.2.The addition of W0.2 and Mo0.2 make CoCrFeNiW0.2/Mo0.2 HEAs remain single FCC solid solution structure,on account of a small amount of W and Mo can be completely dissolved in the alloy lattice,which can not cause the phase structure change.With the further promotion of W and Mo content,CoCrFeNiW0.5/Mo0.5 HEAs are respectively precipitated with W rich and Mo rich intermetallic phases on the basis FCC solid solution structure,the new precipitated intermetallic phases are distributed along the interdendritic.The addition of W and Mo elements can improve the electrochemical corrosion resistance of CoCrFeNi HEA in seawater,the secondary passivation phenomenon appeared in CoCrFeNiW0.5/Mo0.2 HEAs.In addition,the CoCrFeNiW0.5 HEA shows the best corrosion resistance,the pitting potential reached1.112 V,which was significantly higher than that of the as cast CoCrFeNi HEA of0.157 V;the passivation range is increased from 1.155 V to 2.291 V,and the stability of the passive film is greatly improved.Adding W and Mo elements can significantly improve the hardness and the yield strength of CoCrFeNi HEA,the enhancement of mechanical properties of W0.2 and Mo0.2 alloys is related to solid solution strengthening,while the strengthening mechanism of W0.5 and Mo0.5 alloys are solid solution strengthening and second phase strengthening.Among them,the microhardness of Mo0.5 added HEA reach 356 HV,the yield strength and ultimate compressive strength are respectively 604 MPa and 1724 MPa,and the ultimate strain is up to 49.1%,which shows excellent comprehensive mechanical properties. |
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