Effect of Nb on Microstructure and Wear Property of Laser Cladding CoCrFeNiTiNbx High-Entropy Alloys Coatings

A group of CoCrFeNiTiNb_x high entropy alloys (HEAs) coatings were produced by laser cladding. The effect of Nb content on the microstructure and wear resistance of the HEAs coatings was investigated. The results indicated that adding Nb promoted the phase transition from BCC to FCC and the formation of Fe₂Nb Laves phase, The diffraction peaks of FCC and BCC phases were firstly shifted to smaller angle as Nb content was increased, and then shifted to larger angle. Adding Nb promoted brittle fracture of more coarse dendrites to formed fine dendrites and equiaxed crystals homogenizing the microstructure in the HEAs coatings, as well as the formation of dense dislocations and dislocation interaction. The microhardness of the HEAs coatings was firstly increased and then decreased as Nb content was increased, and the change of the mass loss and friction coefficient was opposite trend. Compared with CoCrFeNiTiNb_0.0 HEAs coatings, the microhardness of the CoCrFeNiTiNb_1.0 HEAs coatings was improved by 25.00%, the mass loss was reduced by 28.27%, and and friction coefficient was the lowest. The wear mechanism of the HEAs coatings was transformed from the adhesive wear and oxidative wear accompanied by the abrasive wear to the abrasive wear accompanied by the adhesive wear and oxidative wear as Nb content was gradually increased.