Impact of Nb and Zr on the precipitation evolution of Laves phase and the properties of laser cladding coating of AlCoCrFeNi high entropy alloy

Abstract

The impact of Nb, Zr, and their synergies on the phase composition, wear and high oxidation resistance of a high entropy laser cladding coating consisting of AlCoCrFeNi on Q235 steel was thoroughly investigated in this work. From our analysis, it was demonstrated that the addition of Nb and Zr promoted the formation of the Laves phase except the BCC phase, and a small amount of MC phase was formed in the coatings containing Zr. Although both of them can refine the grain to different degrees, the grain refinement degree was the highest when they were added together. The solid solution strengthening, fine crystal strengthening, and Laves phase precipitation strengthening induced by the addition of Nb and Zr can significantly improve the microhardness of the coating, which was 1.1–1.5 times that of S1-S3 coatings. The formation of ternary Laves phase, grain refinement, and increase of the microhardness enhanced the plastic deformation and micro-cutting resistance of S4 coating, and the wear resistance was 1.3–2.5 times that of S1-S3 coatings. The unstable oxide Nb2O5 produced by the addition of Nb led to a reduction in the stability of the oxide layer. However, when the two were added cooperatively, the formation of unstable oxide Nb2O5 was reduced by the presence of Zr. Moreover, grain refinement was induced by the collaboration of the two making the protective oxide layer form faster, and stronger bonding with the coating, the high temperature oxidation resistance was significantly improved, which was 1.3–4.3 times that of S1-S3 coatings.