Effect of Nb components on the microstructure and mechanical properties of high-entropy alloy coatings

CoCrFeNiTi_0.8Nb_y (y = 0.25, 0.5, 0.75, 1.0) coatings were prepared on the surface of Q235 steel using laser cladding. The phase structure and microstructure of the coatings were analyzed by optical microscope (OM), X-ray diffractometer (XRD), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The hardness and wear resistance of the coatings were tested by micro-Vickers hardness tester and friction wear tester. The results show that the microstructure shows a typical dendritic crystal structure, and the addition of Nb elements decreases the size of the grains; by increasing the content of Nb elements, the crystal structure of the high-entropy alloy coatings consists of BCC phases, a small amount of FCC phases, and Fe₂(Ti, Nb)-type Laves phases; the microhardness of the coatings is improved by the combined effect of fine-grained reinforcement, solid solution strengthening, and the strengthening of the second phase; The presence of the intermediate phase can hinder the plough cutting process to a certain extent, which improves the wear resistance of the coating; CoCrFeNiTi_0.8Nb_0.75 coating has the best hardness and wear resistance, the hardness of 710 HV, about 4 times that of the substrate, and the coating has the smallest amount of abrasion, and the abrasion marks are relatively flat.