In this paper, Fe-based and Co-based alloy powders were chosen to perform laser cladding on wheel materials through conventional laser cladding (CLC) and ultra-high-speed laser cladding (UHSLC) processes, respectively. The microstructures, element distribution, phase composition and hardness of the Fe-based alloy and Co-based alloy coating layers using the CLC and UHSLC processes were compared and analysed. The results show that the CLC and UHSLC alloy coatings were dense and free of defects such as pores and cracks. Compared with the CLC alloy coating, the grain size of the UHSLC alloy coating was smaller, the coating composition was close to the powder design composition, and the distribution of Cr within and between the grains was more uniform. The Fe-based coating was mainly composed of (Fe, Ni) and Cr₇C₃, and the Co-based coating was mainly composed of γ-Co and Cr₂₃C₆. It was found that the cooling rate of the CLC alloy coating was smaller than that of the USHLC, and the hardness of the CLC alloy coating was less than that of the USHLC. The average hardness of the UHSLC Fe-based and Co-based alloy coatings was 709 HV and 525 HV, respectively. The average hardness of the CLC Fe-based and Co-based alloy coatings was 615 HV and 493 HV, respectively. The rolling friction and wear tests were carried out with the CLC-treated and UHSLC-treated wheel specimens on the GPM-30 rolling contact fatigue testing machine. The results showed that the wear rate of the UHSLC alloy coating on the wheel specimens was significantly lower than that of the CLC alloy coating on the wheel specimens. The wear rates of the UHSLC Fe-based and Co-based alloy coatings on the wheel specimens were reduced by 40.7% and 73.8%, respectively. It was demonstrated that the wear resistance of the USHLC alloy coatings was better than those of the CLC alloy coatings. The CLC alloy coating exhibited more severe fatigue damage with small cracks. Furthermore, the damage of the UHSLC alloy coating was relatively minor, with slight spalling. The Co-based alloy coating exhibited superior wear properties with the same laser cladding process.

The wheel pair is a key component of the subway. Routes of subway conditions are more complex, while frequent starting and braking are more likely to cause wheel damage. To improve the sliding tribological properties of subway wheels, this article focused on laser-cladding technology to repair the wheel. Ni-based and Fe-based alloy coatings were prepared. The microstructure of the coatings was studied by SEM, EDS, XRD, and 3D optical morphology. The mechanical properties of the coating were studied by the Vickers microhardness tester and MFT-EC4000 reciprocating electrochemical friction and wear tester. There are mainly γ(Ni, Fe), Cr₇C₃, Cr₂₃C_6, and other phases in the Ni-based coating, and there are mainly γ-Fe, (Fe, Ni), (Fe-Cr-Ni) solid solution and other phases in the Fe-based coating. The hardness of the Ni-based coating is 250 HV_0.7, which is essentially the same as the hardness of the substrate. The hardness of the Fe-based coating reaches a maximum of 715HV_0.7. The hardness of the Fe-based coating is 2.86 times higher than the hardness of the substrate. The Fe-based coating is strengthened by the solid solution due to the existence of the solid-solution phase. The Ni-based coating in high-temperature performance is general. Its hardness and friction performance were also ordinary. The results of the study can provide theoretical and technical guidance for the application of laser-cladding technology on subway wheels.