To determine the influence of the BaF₂-CaF₂ eutectic addition amount on the microstructure, microhardness, and dry sliding frictional and wear properties/maintenance properties of the ZrB₂/NiCr composite coating obtained by laser cladding. The composite coatings with BaF₂-CaF₂ addition amounts of 0, 0.5, 1, 1.5, and 2 wt.% were fabricated on the surface of 304L stainless steel using the coaxial laser cladding technology. The phase composition, microstructure, microhardness, and wear resistance of the coatings were characterized and tested. The results show that the coatings are mainly composed of γ-Ni solid solution, residual ZrB₂, in-situ CrB hard phase, and Cr₂O₃, etc. The addition of BaF₂-CaF₂ slightly reduces the microhardness of the coating, and the differences among different addition amounts are small. The hardness is mainly dominated by ZrB₂ and in-situ CrB hard phases. With the increase in the addition amount of BaF₂-CaF₂, the friction coefficient and wear rate of the coating show a trend of first decreasing and then increasing; at 1.5 wt.% addition amount, they are the lowest, being 0.30 and 0.84×10⁻⁵ mm³/N·m respectively. The wear mechanism is mainly abrasive wear at low addition amounts, and gradually changes to oxidation wear with the gradual increase of the BaF₂-CaF₂ eutectic addition amount, forming a dense friction oxide layer (Tribo-oxide layer) composed of NiO, Cr₂O₃, ZrO₂, and the BaF₂/CaF₂ lubricating film on the surface. At the same time, the addition of BaF₂-CaF₂ eutectic can refine the grain size and change the solidification behavior of the composite coating pool. An appropriate amount of BaF₂-CaF₂ can significantly improve the wear resistance of the coating through the synergistic effect of the lubricating film and oxide film, while excessive addition leads to the peeling-off of the oxide layer and a decline in the overall performance.
 

Laser cladding; NiCr coating; BaF2-CaF2 eutectic; Wear mechanism