41 / 2021-06-29 10:05:47

Design and tribological behavior of nano-lamellar Ni1.5CrCoFe0.5Mo0.1Nbx eutectic high-entropy alloy coatings by laser cladding

Eutectic high-entropy alloy coating,Laser cladding,Microstructure evolution,Tribological behavior

In order to study the microstructure evolution of laser-cladded eutectic high-entropy alloy (HEA) coatings during the non-equilibrium solidification process with rapid cooling speed. In this work, a novel Ni_1.5CrCoFe_0.5Mo_0.1Nb_0.68 eutectic HEA coating with nano-lamellar microstructure was successfully designed by binary eutectic compositions strategy, thermodynamic calculation and simple experimental approach. Compared with the predicted eutectic compositions, the actual eutectic composition has a higher Nb content due to the increased solid solubility of Nb in the FCC phase affected by the rapid cooling speed. The Ni_1.5CrCoFe_0.5Mo_0.1Nb_x (x = 0.55 hypoeutectic, 0.68 eutectic, 0.8 hypereutectic) HEA coatings were prepared by laser cladding, which are all composed of FCC phase and Laves phase. Typical eutectic lamellar and hypoeutectic/hypereutectic microstructures were obtained at the central regions of the coatings, while the lamellar eutectic microstructure is broken and columnar crystals formed at the interfacial regions. The different ratio of the temperature gradient (G) and the solidification rate (V) and heat flux direction lead to the distinct microstructure evolution process of central regions and interfacial regions. The average micro-hardness of Nb_0.55, Nb_0.68 and Nb_0.8 coatings were calculated as ~573.5 HV, ~665.8 HV and ~715.6 HV respectively. From x = 0.55 to x = 0.8, the wear resistance of Ni_1.5CrCoFe_0.5Mo_0.1Nb_x HEA coatings are increased, and the dominant wear mechanism of the HEA coatings transforms from adhesive wear to abrasive wear.