Effect of laser claddings of Fe-based alloy powder with different concentrations of WS2 on the mechanical and tribological properties of railway wheel

Laser cladding could be applied on railway wheels to improve their service lives. Fe-based alloy powder is widely used as the laser cladding material due to its good self-fluxing ability and low price. However, the friction coefficients and wear rates of Fe-based alloy laser claddings are high. WS2 is used as the additive for common laser cladding treatment, while it has not been used for claddings on railway wheels. Understanding the influence of WS2 concentration on the mechanical and tribological properties of Fe-based alloy laser claddings on railway wheels has significance for extending the application of laser treatment on railway transit. Therefore, laser claddings of Fe-based alloy powders with different contents of WS2 powder (0, 2%, 4%, 6%, 8%) were produced on the railway CL60 wheel material. Rolling-sliding tests were conducted on a twin-disc tribometer using the uncladded and cladded wheel samples against an uncladded U71Mn rail sample. The results indicated that the microstructure of laser claddings was composed of dendritic and eutectic phases. With the increase in the WS2 content from 0 to 6%, the size of dendritic phases was decreased from around 20 μm to less than 10 μm. With 8% WS2, the size of dendritic phases was increased to around 10–20 μm. Laser claddings of Fe-based alloy powders with WS2 included (Fe, Ni) and (Fe, Si) solid solutions, hard carbide (Cr7C3), Ni–Cr–Fe, and CrS phases. The hardness was increased to 730–820 HV0.5 and residual stresses were changed to be compressive state. Rolling contact fatigue (RCF) cracks preferentially initiated and developed along the boundary between dendritic and eutectic phases. The smallest wear rate and shortest RCF cracks occurred on the cladding from powders with 6% WS2. Thus, the optimum content of WS2 in the Fe-based alloy powder was 6% for laser cladding on the railway wheel material.