Effect of niobium content on microstructure and wear and corrosion resistance of laser-clad FeCo0.5CrNi1.5B0.5Nbx coatings on ductile iron

Abstract

Ductile iron with a high carbon content is highly susceptible to the precipitation of brittle carbides during the cladding process, which makes it challenging to achieve the desired formability of the coating. In this study, FeCo0.5CrNi1.5B0.5Nbx (x = 0.1, 0.2, 0.3, and 0.4) high-entropy alloy coatings were designed using theoretical calculations and prepared on ductile iron through laser cladding. The effect of niobium (Nb) content on the microstructure evolution and phase composition of the coating was explored to determine the alloy component with the highest wear and corrosion resistance. All of the prepared coatings consisted of face-centered cubic (FCC) phases, along with Nb(C, B2) and Laves phases. With the increase in Nb content, the intensity of the diffraction peaks of NbC significantly increased compared to those of the other precipitates due to element diffusion. Nb0.3 coatings, which had the highest hardness, H/E, and H3/E2 values due to the most suitable percentage of FCC and hard phases, presented the lowest average friction coefficients of 0.48, 0.49, and 0.50, as well as the minimum wear volume of 0.64 × 108, 2.06 × 108, and 5.04 × 108 μm3 under loads of 10, 30, and 50 N, respectively. The wear mechanism of all the coatings was dominated by adhesive wear and oxidation wear under loads of 10 N and 30 N, while it changed to abrasive wear under a load of 50 N. Furthermore, Nb0.3 coatings also showed superior corrosion resistance due to the positive influence of the optimal Nb content on the oxide film. The Ecorr values were − 395 mV and − 337 mV, and the Icorr values were 0.21 × 10−6 A/cm2 and 1.10 × 10−6 A/cm2 in NaCl (3.5 wt%) and HCl (0.5 mol/L) solutions, respectively.