Microstructure and wear resistance of multi-layer graphene doped AlCoCrFeNi2.1 high-entropy alloy self-lubricating coating prepared by laser cladding

Abstract

A novel AlCoCrFeNi_2.1 high-entropy alloy self-lubricating coating was prepared by multilayer graphene (MLG) enhancement. The AlCoCrFeNi_2.1-MLG (3 wt%) high-entropy alloy self-lubricating coating was prepared on AISI1045 steel using laser cladding by introducing lubricant named MLG. The microstructure, phase structure, wear resistance and corrosion performance of the AlCoCrFeNi_2.1-MLG coating were studied. It is shown that the microstructure of the AlCoCrFeNi_2.1-MLG coating has typical dendritic (DR) and interdendritic (ID) structures, with the dendrites consisting of high density M₂₃C₆ phase precipitation and FCC phase distributed in the interdendritic region. With the addition of MLG, the average hardness of the AlCoCrFeNi_2.1 coating increases from 306.71 HV to 486.68 HV (an increase of 58.68 %). The average coefficient of friction decreases from 0.59 to 0.48 (a reduction of 22.92 %). The wear rate decreases from 1.678 × 10^{- 6} mm³·N^{− 1} m⁻¹ to 0.825 × 10^{- 6} mm³·N^{− 1} m^{− 1} (a reduction of 50.83 %). This is due to the formation of a lubricant film in the AlCoCrFeNi_2.1-MLG coating. The wear mechanism changes from plastic deformation and abrasive debris wear to slight delamination and spalling of the lubricant film. However, the corrosion performance of the AlCoCrFeNi_2.1-MLG coating is slightly reduced by the occurrence of micro-electro-coupling corrosion on the corroded surface. The M₂₃C₆ phase is used as the anode and the FCC phase is used as the cathode. The subsequent generation of a passivation film prevents the appearance of severe electro-coupling corrosion. The wear resistance of the AlCoCrFeNi_2.1-MLG coating is substantially improved while taking into account the corrosion performance. This study provides important values for laser cladding of self-lubricating composite coatings of high-entropy alloys.