Comparative study on the microstructure and mechanical properties of Ni625 alloy deposited by conventional and ultra-high-speed laser cladding for the repairing of EA4T railway axle steel

This study compares the microstructure and mechanical properties of Ni625 alloy coatings produced by conventional laser cladding (CLC) and ultra-high-speed laser cladding (UHSLC) for the repair of EA4T railway axle steel. The results demonstrate that the UHSLC process, characterized by lower heat input and faster cooling rates, significantly improves cladding efficiency and reduces the size of the heat-affected zone (HAZ) in the substrate compared to CLC under typical processing conditions. The UHSLC coating exhibits more uniform and finer grains, with a significantly lower dilution rate compared to the CLC specimen. The hardness of the UHSLC coating is higher, approximately 300 HV, compared to 275 HV for the CLC coating. In tensile testing, the ultimate tensile strength and yield strength of the UHSLC specimen are closer to the base material, and the fracture mode shows ductile-brittle mixed characteristics. In contrast, the CLC specimens are more prone to crack initiation at the coating-substrate interface, exhibiting higher brittleness and larger residual stresses. The UHSLC process demonstrates significant advantages over the CLC process by refining the grain structure, reducing the size of the HAZ, and lowering residual stresses. These benefits provide a theoretical foundation for the selection and optimization of parameters in subsequent modification processes for railway axle steel.