Effect of the Nb content on the microstructure evolution and properties of the CrFeCoNiNbx layers prepared by laser cladding

Abstract

Marine engineering components, such as ship stern shafts, are often subject to local overload, wear and seawater erosion. In order to improve the performance and service life of marine engineering components, the CrFeCoNiNb x ( x = 0, 0.25, 0.5, 0.75 and 1) high-entropy alloy (HEA) coating were prepared on the 42CrMo substrate by laser cladding. The microstructure, microhardness, wear behaviour and the corrosion resistance of the prepared HEA coatings with different Nb contents were evaluated. Results show that the cladding layer of CrFeCoNiNb0 is composed of single dendrites with a small amount of short rod-shaped protrusions distributed along the dendrites. The addition of Nb promotes growing of the original dendrite structures into interdendritic structures with internal substructures retained. Apart from the variations in the microstructure, the formation of the Laves phase, which is both hard and corrosion resistant, is also an important factor in the performance of the cladding. This variation leads to the increase of the microhardness of the cladding layer, accompanying with the improvement of wear resistance property. Notably, the improvement of microhardness is ascribed to the combined contribution from the refinement strengthening, the solid-solution strengthening and the dispersion strengthening by Laves phase. The improvement of the corrosion resistance is mainly attributed to dense passivation film formed by the Cr and Nb on the surface of the cladding layer. The above results suggest that the CrFeCoNiNb x cladding layer could achieve synergistic interaction between the mechanical properties and the corrosion resistance on stern shaft surface.