Microstructure and magnetic properties of NiCrMoAl/WC coatings by laser cladding: Effect of WC metallurgical behaviors

The NiCrMoAl/WC composite coatings with different contents of WC particles were deposited on P550 steel by laser cladding. The microstructure and magnetic properties of the coatings were characterized by SEM, EDS, XRD and VSM. The magnetism of phases was calculated by the first-principles based on the density functional theory. The results show that the coatings are mainly composed of γ-Ni, WC, W2C, Ni2W4C, Ni3Mo3C, Mo2C and Al4C3. The relative permeability of the coatings increases from 1.002 to 1.080 with the increase of WC percentage from 24 wt% to 60 wt%. The phases of WC, W2C, Ni2W4C and Al4C3 are non-magnetic, Ni3Mo3C and Mo2C are weakly magnetic according to the calculations. The weak magnetism of Ni3Mo3C originates mainly from the strongly correlated interaction of 3d electrons in Ni atoms, whereas that of Mo2C originates mainly from the d-state electrons of Mo atoms. The weak magnetism of the coatings (WC ≥ 48 wt%)is related to the metallurgy behaviors of WC particles. The C elements resulting from the decomposition of WC particles can be diffused into the Ni-based alloy, thus resulting in the formation of weakly magnetic phases in the cladding layer, such as Ni3Mo3C and Mo2C.