Effect of Nb addition on microstructure and properties of laser cladding NiCrBSi coatings

NiCrBSi coatings with different Nb additions have been prepared by laser cladding. The microstructure, phase composition, hardness, and wear resistance of the coatings were studied by scanning electron microscopy (SEM), electron probe microanalyser (EPMA), X-ray diffraction (XRD), microhardness tester and M-200 wear tester. The results show that the phases in the NiCrBSi coating without Nb addition include gamma-Ni, Cr23C6, Cr7C3, Ni3B, Ni3Si2 and CrB. The NbC phase appears in coatings after the addition of Nb element. When the addition of Nb is 2 wt-%, the NbC particles with a size of about 1.2 mu m were found in the coating, and the amount of NbC is about 1.8 vol.-%. With the increase of Nb addition, the size and amount of NbC in the coatings also increased. When the addition of Nb is 6 wt-%, the size of NbC is about 2.3-6.1 mu m and the morphology of NbC changed from particle to quadrangular and petaloid shaped. In addition, when the addition of Nb is 2 wt-%, the hardness and wear resistance of the coating are the best, and the wear resistance of the coating is 104% higher than that without Nb addition.