Effect of Scanning Path on Residual Stress and Tribological Properties of Multi-pass Laser Cladding Layers

Laser cladding technology is widely used in the field of surface protection and remanufacturing because of its advantages, such as metallurgical bonding between the cladding layer and substrate, high processing efficiency, low dilution rate, and high energy input. It improves the wear resistance and corrosion resistance of the substrate, as well as the life of the cladding layer of the parts. However, instantaneous melting and rapid solidification of the melt pool during the laser cladding process lead to uneven stress within the cladding layer. It has been shown that even if the basic parameters are the same, the scanning paths and scanning time intervals of different lasers significantly influence the temperature distribution, and an uneven temperature distribution further leads to an uneven distribution of thermal stresses, which can cause coating quality issues. To analyze the effect of the scanning paths on the residual stress and tribological properties of the multi-pass laser cladding layer, a multi-pass laser cladding layer of Inconel 718 was prepared on 316L stainless steel using different scanning paths, and the distribution of residual stress in the cladding layer was investigated based on the thermoelastic-plastic model and the residual stress analyzer. The microstructure and hardness distribution of the cladding layer were studied using an X-ray diffractometer, a metallurgical microscope, and a hardness testing system. The tribological properties of the cladding were evaluated using a comprehensive material surface property tester and a laser confocal microscope. The results show that, owing to the difference in temperature cycling during the cladding process, the reciprocating scanning path has the shortest interval between each cladding pass and the lowest surface residual stress. The isotropic and dispersive scanning paths exhibit intermediate surface residual stress levels, while the shrinkage scanning path, which has the largest accumulation of heat in the central region of the cladding layer, exhibits the highest surface residual stress. The isotropic scanning path results in the most homogeneous microstructure due to the differences in temperature cycling during the process. In terms of microstructure, the isotropic scanning path exhibits the most uniform microstructure. Due to the consistent time intervals between each fusion cladding pass, the cooling process remains stable, resulting in minimal changes in crystal size from the cladding layer to the fusion zone. The shrinkage path has the largest accumulation of heat in the fusion cladding layer, and the low cooling rate allowed the crystals more time to grow, which resulted in significant changes in the size of the crystals at the bottom. Owing to the differences between the primary arm spacing and the volume fraction of the Laves phase in the fused cladding, the isotropic scanning path has a uniform distribution with a low content of the Laves phase and the lowest abrasion rate of the fused cladding layer. The reciprocating and dispersive scanning paths have intermediate abrasion rates, while the shrinkage-type scanning path has the highest abrasion rate due to its larger number of Laves phases. Therefore, a reciprocating scanning path should be selected for multi-pass cladding to reduce residual stresses in the cladding layer, and an isotropic scanning path should be selected to reduce the wear rate of the cladding layer. The results of the different scanning paths are expected to provide a theoretical basis for the selection of process parameters in the fields of surface protection and remanufacturing.