Nb doping in laser-cladded Fe25Co25Ni25(B0.7Si0.3)25 high entropy alloy coatings: Microstructure evolution and wear behavior

The influence of Nb doping on the structure evolution, hardness and wear behaviors of laser-cladded (Fe0.25Co0.25Ni0.25(B0.7Si0.3)0.25)100-xNbx (denoted as Nbx hereafter, x = 0, 1, 2, 3 and 4 at.%) high entropy alloy coatings were analyzed. Detailed characterization indicated that the microstructures evolve from face-centered cubic (FCC) and (Fe, Co, Ni)2B phases of the Nb-free coating to FCC, (Fe, Co, Ni)2B and amorphous phases of the Nb-containing coating (1 ≤ x ≤ 2). Notably, the glass formation ability of the coating is enhanced with the addition of Nb. As the Nb content further increases (3 ≤ x ≤ 4), it promotes the fully crystalline structures of body-centered-cubic (BCC), Laves, FCC and (Fe, Co, Ni)2B phases. The average crystalline size of the coating is refined from 3.5 to 1.3 μm as a function of Nb content. The wear resistance of the coatings improves firstly and then aggravates with increasing of Nb content, which corresponds to the variation trend of microhardness and microstrain. The Nb2 coating shows a maximum hardness value of 11.9 Gpa and excellent wear resistance due to the formation of amorphous structure and good elastic properties. The phase prediction in the coating was calculated by thermodynamic parameters. The relationships between the structure and properties of the present coating were elucidated. The new metal-metalloid high entropy metallic glassy coating and superior properties give its good promise for engineering applications. •Fe25Co25Ni25(B0.7Si0.3)25 high entropy alloy coatings with different Nb addition were prepared by broadband laser cladding.•Hardness and wear resistance of the coating first increased and then decreased as Nb content increasing.•Microstrain was used to evaluate the effect of Nb addition on the structure of the coating.•The coating with 2 at.% Nb displays maximum amorphous fraction, hardness and wear resistance.