Study On Preparation,Microstructure,and Properties Of High Entropy Alloys CoCrFeNi-M

TheCoCrFeNi-M alloys consisting of transition elements Fe,Co,Cr and Ni are the most attracting HEA system with excellent properties such as high strength,low temperature performance,soft magnetic property,oxidation resistance,wear resistance,corrosion resistance and radiation resistance.As novel structural and functional materials,these alloys are have potential applications in metallurgy engineering,electric power,marine and other engineering fields.Transition element molybdenum(Mo),metallic element aluminum(Al),and rare earth element yttrium(Y)have different mixing enthalpies with those of the elements in FeCoCrNi.In this work,the elements Al,Mo and Y were selecte to design and prepare high strength HEAsCoCrFeNi_z-M(Al_x,Mo_y,Y_w)with(FCC+BCC)structures and excellent corrosion resistance.The HEA ingots were prepared by vacuum arc melting and the HEA coatings were prepared by laser cladding.The Metallurgical effects of the three elements on the elements in FeCoCrNi were studied,and the effects of the nano precipitates on microstructure,mechanical property,and corrosion resistance were studied.The main research results are as follows.(1)Based on first principles and Monte Carlo method,the cell models of the multicomponentCoCrFeNi-M(Al,Cu,Mo)alloys were established by using special quasi-stochastic structure and periodic maximum entropy stochastic structure.Elements of Al,Cu,and Mo were added intoCoCrFeNi alloys,respectively.Their effects on the element distribution and the short-range-order factor of the system were discussed.The effects of the combined addition of Mo and Al on the near-range ordered distribution of the atoms inCoCrFeNi-M alloy were studied,and the HEAsCoCrFeNi-M(Al,Mo)were determined to be the main alloy system for metallurgical experiments.(2)The metallurgical effects of elements Al,Mo,and Y in the alloys were studied.The results show that fine duel-phase(FCC+B2)with uniform composition can be obtained when both Al and Mo elements are added into the FeCoCrNi-M alloys.The AlCoCrFeNi_zY_wingots with trace addition of rare earth element Y have a(FCC+B2)eutectic structure with a lamellar spacing of about 1?m.(3)The nano phase precipitation and strengthening mechanisms due to Al,Mo,and Y additions in FeCoCrNi_z-M(Al_x,Mo_y,Y_w)ingots were studied.The results show that the Mo addition promoted nano precipitation in FCC phase and B2 phase,which caused an increase in compressive strength by 93.18%,compressive ductility by 24.19%.The FeCoCrNi_2.1Al Y_wingots with trace Y addition have a(FCC+B2)eutectic structure.When Y<0.1%,the dissolved Y can distort lattice,refine microstructure,and increase yielding strength.When 0.5%?Y?1.0%,double yielding occurred at a compressive deformation of about 2.5%,causing an increase in yielding strength by 40%.(4)The powers of HEAs FeCoCrNi_z-M(Al_x,Mo_y)were designed and used to prepare high strength corrosion resistant coatings by laser cladding technology on the surface of Q235B hot rolled steel plate.The metallurgical reaction of the powder with steel and the microstructure and properties of the coatings were studied.The microstructure and mechanical testing results show that the coating is(FCC+B2)eutectic structure with an average hardness of about 310HV.The coating is metallurgically bonded to the substrate,the microhardness of the bonding zone is 33.33%higher than that of the substrate,and the coating has good corrosion resistance.The coating structure of AlCoCrFe Mo Ni_2.2is(FCC+BCC+B2),the average hardness of the coating is 490 HV,and corrosion resistance of the coating is good.The hardness of the coating and substrate joint is about 150HV which is 42.86%higher than that of the substrate.It is found that the Al_1.2CoCrFeNi_2.1and AlCoCrFe Mo Ni_2.2coatings with(FCC+BCC(or B2))structure have high strength,toughness and corrosion resistance.