Microstructure and tribological performance of laser cladding Co-Based laser coatings with h-BN and Fe addition

To enhance the hardness and wear resistance of SS400 structural steel while mitigating coating crack defects, this study employs laser cladding technology to fabricate two distinct coatings: Stellite 1+Fe and Stellite 1+Fe+h-BN, applied to the surface of SS400 structural steel. The microstructure, hardness, and wear-resistant performances of these coatings are systematically characterized by using scanning electron microscope, hardness tester, and friction and wear machine. The results demonstrate that implementing thermal insulation measures during the laser cladding process, along with using the same powder as the substrate, effectively reduces the crack sensitivity of the coating. Consequently, a high-quality coating, devoid of cracks and porosity defects, is achieved. Contributions to hardness enhancement include diffusion strengthening, fine grain strengthening, and solid solution strengthening of Cr carbides in the coating. Additionally, the in situ generation of CrB and CrN in the hBN-containing coatings further contributes to hardness improvement. The attained hardness values for Stellite 1+Fe and Stellite 1+Fe+h-BN are 572.88 HV0.5 and 427.30 HV0.5, respectively, representing 2.29 times and 1.71 times the substrate hardness, respectively. Both coatings significantly enhance the wear resistance of the substrate. However, the primary wear mechanism shifts from adhesive wear to abrasive wear after the addition of hBN. This transition is accompanied by a reduction in the average coefficient of friction of the coatings from 0.390 to 0.220. Additionally, the wear rate decreases from 0.193x10- 3 mm3/Nm to 0.069x10- 3 mm3/Nm, attributed to the favorable self-lubricating performance of h-BN. Consequently, the Stellite 1+Fe+h-BN coating exhibits superior wear resistance compared to the Stellite 1+Fe coating.