Effects of Cr incorporation on the microstructure, tribological and mechanical properties of laser cladding (TiNbTaZr) 100-x Crx (x = 0, 5, 10, 20) high entropy alloy coatings

Abstract

Refractory high entropy alloy (RHEA) coatings have a wide application space in the field of titanium alloy surface protection. TiNbTaZr RHEA is a typical system of RHEAs which has excellent plasticity but insufficient strength, it is necessary to improve the strength of TiNbTaZr RHEA. In this work, laser cladding (TiNbTaZr) _100-x Cr_x (x = 0, 5, 10, 20) RHEA coatings are prepared on the surface of Ti-6Al-4 V substrate to overcome the damage of Ti-6Al-4 V substrate under wear and alternating stress. The effects of Cr incorporation on the microstructure evolution mechanism, mechanical and tribological properties of coatings are discussed in system. The results show that Cr can form Laves phase with other elements, the content of Laves phase increase with Cr content. Laves phase can improve the mechanical and tribological properties of the TiNbTaZr coating. (TiNbTaZr)₈₀Cr₂₀ coating with a higher compressive strength (2202.77 MPa) and ultimate fracture strain (25.6 %) exhibits a balance of strength and ductility, the reticulated structure formed by BCC phase prevents the decrease in ductility caused by the hard Laves phase. Meanwhile, the coatings have better tribological properties with the increase of Cr content, the (TiNbTaZr)₈₀Cr₂₀ coating possesses the lowest average friction coefficient (0.439) and the lowest wear rate (1.48 × 10⁻⁴ mm³/ (N·m)). Due to the oxidation reaction of Cr element, an oxide film is formed on the surface of the (TiNbTaZr)₈₀Cr₂₀ coating which has a positive effect on the tribological properties, the (TiNbTaZr)₈₀Cr₂₀ coating has better tribological properties compared to other three coatings.