Effect of Y₂O₃ content on microstructure and properties of Ni-based self-lubricating composite coating

In order to improve the wear resistance and corrosion resistance of sucker rod surface, Ni-based self-lubricating composite coating with Y2O3 was successfully prepared on 35CrMo steel substrate by high frequency induction heating cladding technology. The coating structure is uniform and dense, and there are no obvious defects such as pores and cracks. The microstructure of the coating layer was studied by means of metallographic microscope, scanning electron microscope and X-ray diffractometer. The hardness, wear resistance and corrosion resistance of the coating layer were tested by microhardness testers, friction and wear testers and electrochemical workstations. The results show that the main phases of the composite coating are γ- (Ni, Fe), Ni3Fe, CrB, TiC and Cr23C6. When the addition amount of Y2O3 is 2%, the average microhardness of the composite coating is the highest, which is 805.1 HV0.2; under the same wear conditions, the wear resistance of 2% Y2O3 composite coating is the best. The average friction coefficient and wear loss are reduced by 16.27% and 20.35% respectively compared with the composite coating without rare earth, and 37.55% and 48.02% respectively compared with the substrate. The wear mechanism of the composite coating is mainly severe adhesive wear, and there is a small amount of oxidation wear. With the increase of Y2O3 content, the self-corrosion potential of the composite coating fluctuates in a small range, and its self-corrosion current density decreases first and then increases. The self-corrosion potential of the composite coating containing 2% Y2O3 is more positive (–0.4316 V), and the self-corrosion current density is the smallest (3.9579 µA · cm−2), and its corrosion resistance is the best.