Microstructure And Properties Of Laser Cladding CoCrFeMnNiC_x High Entropy Alloy Coating

High entropy alloy CoCrFeMnNi has been widely concerned for its special simple FCC solid solution structure,impurity phase which is not inclined to form intermetallic compounds,excellent mechanical properties,wear resistance and corrosion resistance.In this paper,the coating material CoCrFeMnNi C_xwith good cladding performance,mechanical properties and wear resistance is formed by the combination of theoretical derivation and experimental verification,and the nano carbon ball is used as additive to mix the two into the high entropy alloy CoCrFeMnNi powder.Firstly,the thermodynamic conditions of crystal structure,atomic size,electronegativity and enthalpy of mixing entropy are studied by theoretical calculation.By summarizing the previous preparation technology and strengthening methods of CoCrFeMnNi high entropy alloy,the parameters of this experiment are determined as laser power(3.7 k W and 4.2 k W),laser scanning speed(120 mm/min,200 mm/min,350 mm/min,400 mm/min)and the composition of the coating material CoCrFeMnNi C_x(x=0,0.03,0.06,0.09,0.12 and 0.15).After the coating is prepared,the phase structure,microstructure and element distribution of the coating are analyzed and tested by macroscopic observation,XRD,OM,SEM,EDS,EPMA,and the mechanical and wear resistance of the coating are tested by microhardness tester,friction tester and electrochemical workstation.The results show that the change of laser process parameters has no obvious effect on the phase structure,but with the increase of laser power or the decrease of scanning speed,the dilution rate of coating increases,the microstructure becomes thick,and some columnar crystal areas are replaced by cellular crystal region,and the hardness of coating decreases rapidly.Generally speaking,the faster the scanning speed,the higher the hardness of the coating,the better the wear resistance.However,the coating coating has poor cladding performance and uneven surface quality due to the fast laser scanning speed,which makes the wear resistance of the coating obtained at 400mm/min is poor.The C content has a certain influence on the macro morphology of laser cladding coating.With the increase of C content,the coating coating performance becomes poor,the surface quality of the coating becomes poor and the bonding with the substrate is not tight,but the dilution rate of the coating decreases.With the increase of C content from 0 to 0.09,M₂₃C₆phase of carbides was produced and gradually increased in the coating,but when the C content increased from 0.09 to 0.15,the M₂₃C₆phase disappeared from XRD.The microstructure of the coating becomes smaller first and then becomes coarse with the increase of C content.At the same time,when the C content increases to0.12 and 0.15,the upper middle part of the coating is originally the dendrite at the cellular crystal position.When the C content is 0.03?0.09,the main form of C element is M₂₃C₆carbide formed with metal elements Fe and Cr,and it is mainly distributed at the grain boundary;when the C content is 0.12 and 0.15,the C element mainly exists in the form of single substance.When C atom is not added,the average hardness of cladding layer is lower,183.2 HV_0.2;with the increase of C content,the hardness of coating increases gradually,and the average hardness of cladding layer reaches the maximum value 223.48 HV_0.2when x=0.09;then,the hardness of coating begins to decrease gradually with the addition of C atom.At x=0.15,the hardness reaches 195.04 HV_0.2.The wear resistance of high entropy alloy shows the tendency of first strengthening and then weakening with the increase of C content,and the alloy shows a strong wear resistance in a short time when the C content is 0.15.No matter how much C content,the high entropy alloy has obvious passivation effect,which shows that it has good corrosion resistance.With the increase of C content,the corrosion resistance of CoCrFeMnNi Cx high entropy alloy is enhanced first and then weakened,and the minimum corrosion rate of 0.027 mm/a is obtained when the C content x=0.09.