Effect of rotating magnetic field on microstructure and tribological properties of laser cladded nickel-based coatings

Nickel-based coatings were prepared by laser cladding assisted with rotating magnetic field on mild steel substrates. The effects of rotating magnetic field on the defects, microstructure, residual stress, microhardness, and wear resistance of the coatings were studied. Results revealed that the rotating magnetic field reduced pores and cracks of the nickel-based coatings. The nickel-based coatings are main composed of γ-(Ni, M), CrB, M23C6, and NbC phases. The average grain size of the coating decreased from 0.67 μm2 to 0.49 μm2 with rotating magnetic field assistance. The number of large-angle grain boundaries was increased too. At the same time, the residual stress in the coating was significantly reduced by the rotating magnetic field. Therefore, the cracking tendency of the coating was reduced. The average microhardness of the nickel-based coating increased from 422.5 HV0.2 to 515.5 HV0.2 due to fine-grain strengthening. The wear mechanisms of the coatings were mix of abrasive wear and adhesive wear. With rotating magnetic field assistance, the wear resistance of the coating was greatly enhanced. The wear rate of the coating reduced 83.7% from 85.2 μm3/(N∗m) to 13.9 μm3/(N∗m). The wear weight loss reduced 87% from 13.8 mg to 1.8 mg.