Research On Mechanism And Property Of Laser High Entropy Alloying Coatings On Several Alloys

In this paper,high entropy alloy?HEA?coatings were prepared by laser surface alloying on commonly used conventional alloys in industrial fields,such as Fe-base alloy,Ni-base alloy and cp Cu.The constituent phases,microstructure,chemical composition,hardness,cavitation erosion resistance,electrochemical corrosion resistance,wear resistance and high temperature oxidation resistance of the before-and after-heat treated HEAs coatings were investigated by XRD,SEM,EDS,microhardness tester,nanoindentation tester,ultrasonic vibrator measurement,potentiodynamic polarization measurement,friction-wear tester and Muffle furnace,respectively.Meanwhile,the formations of simple solid solution and the rules of phase evolution in HEAs were also explored,aiming at researching and developing novel laser protective coatings with high properties.Experimental results can be drawn as follows:FeCoCrAlCu HEA coating was synthesized on Q235 steel by laser surface alloying.The coating with good metallurgical bonding to the substrate was dense,free of holes or any other metallurgical defects.The FeCoCrAlCu HEA coating,600?-10h and 700?-10h heat treated HEA coatings were composed of BCC solid solution.?-FeCr phases were precipitated in the800?-10h heat treated HEA coatings.The microhardness of the FeCoCrAlCu HEA coating,600?-10h,700?-10h,800?-10h heat treated HEA coatings was 820HV,660HV,520HV and690HV,respectively.The cavitation erosion resistance?Re?of the samples was 2.0,3.1,2.4and 2.5 respectively,indicating that the 600?-10h heat treated HEA coatings exhibited the highest cavitation erosion resistance.FeCoCrAlNiTi,FeCoCrAlNiTi-xTiC and FeCoCrAlNiTi-xCeO₂ HEA coatings were synthesized on 304 stainless steel by laser surface alloying.The FeCoCrAlNiTi HEA coating exhibited FCC+BCC solid solution.The 700?-10h heat treated HEA coatings still exhibited FCC+BCC solid solution,while some intermetallic compounds were precipitated in the 800?-10h and 900?-10h heat treated HEA coatings.The microhardness of the FeCoCrAlNiTi HEA coating,700?-10h,800?-10h,900?-10h heat treated HEA coatings was 630HV,642HV,698HV and 727HV,respectively.The cavitation erosion resistance in 3.5%NaCl solution of the substrate,FeCoCrAlNiTi HEA coating,700?-10h,800?-10h,900?-10h heat treated HEA coatings was only 20%,68%,61%,29%,26%that of the samples in distilled water.The constituent phases of the FeCoCrAlNiTi-x TiC and FeCoCrAlNiTi-xCeO₂ HEA coatings were unchanged before and after heat treatment,and the matrix of the coatings was still FCC+BCC solid solution.The specific wear rate of the FeCoCrAlNiTi,10wt%TiC,30wt%TiC,10wt%TiC-700?,30wt%TiC-700?HEA coatings was 2.437×10^-4 mm³/N m,6.529×10^-5mm³/N m,2.636×10^-5 mm³/N m,1.098×10^-4 mm³/N m,3.542×10^-5 mm³/N m,respectively.The specific wear rate of the 0.5wt%CeO₂,1wt%CeO₂,0.5wt%CeO₂-700?,1wt%CeO₂-700?HEA coatings was 6.44×10^-5 mm³/N m,2.748×10^-5 mm³/N m,8.244×10^-5mm³/N m,3.985×10^-5 mm³/N m,respectively.FeCoCrAlCuNiV_x HEA coatings were synthesized on Ni201 by laser surface alloying.With the increase of V content,HEA coatings have evolved from FCC structure?x=0,0.2?to FCC+BCC structure?x=0.5,0.8,1.0?.After the HEA coatings were heat treated at 700?-10h,the constituent phases of the HEA coatings?x=0,0.2?have evolved from FCC structure to FCC+BCC structure and the HEA coatings?x=0.5,0.8?were unchanged,while some intermetallic compounds were precipitated in the HEA coating?x=1.0?.The oxidation kinetics of the HEA coatings followed a parabolic law,and the HEA coatings?x=0.2,0.5?exhibited the highest high temperature oxidation resistance.FeCoCrAlCu-X_0.5?X=Si,Mo,Ti?HEA coatings were synthesized on cp Cu by laser surface alloying.The constituent phases of the HEA coating for X=Si exhibited FCC+BCC solid solution,while some intermetallic compounds were precipitated in the HEA coatings for X=Mo and Ti.After the HEA coatings were heat treated at 700?-10h,the constituent phases of the HEA coatings for X=Si and Ti were unchanged,while?-FeCr phases were precipitated in the HEA coating for X=Mo.The addition of Mo element can obviously refine the microstructure of the HEA coatings.The HEA coating for X=Mo exhibited a lower elastic modulus and a higher nano-hardness.The HEA coating for X=Si exhibited the lowest corrosion current density,indicating the highest corrosion resistance among the tested samples.Based on mixing entropy(?S_mix),mixing enthalpy(?H_mix),atom-size difference???,valence electron concentration?VEC?and parameter?,the formation rules of simple solid solution in HEAs were systematically investigated.The results showed that the formation of simple solid solution in HEAs cannot be rationalized solely by the high mixing entropy effects.In order to form simple solid solution phases in HEAs,the following conditions have to be satisfied simultaneously below:?S_mix?11.53 J/K mol,-16.48??H_mix?3.2 kJ mol^-1,??1.18,?<6.19.A value of VEC between 7.14 and 8.12 will contribute to the formation of FCC+BCC solid solutions,the BCC phases were stable when VEC<7.14,whereas the FCC phases were found to be stable when VEC>8.12.