Microstructure and tribological properties of in-situ TiC reinforced Ti₂AlNb-based coatings by laser cladding

The TiC reinforced Ti₂AlNb-based coatings were fabricated on the surface of Ti-6Al-4V using Ti, Al, and Nb powder mixtures with different NbC addition (0, 1.25, 2.5, and 5 wt%) by laser cladding to improve the mechanical behavior of Ti-6Al-4V. The effects of NbC on the morphology, microstructure evolution and mechanical properties of the TiC/Ti₂AlNb coatings were studied systematically. Results revealed that the matrix phases of all coatings were mainly composed of lamellar O phase and B2 phase. TiC in situ formed effectively refined grains, in which the length of the B2 grains was reduced from 205.36 μm to 25.31 μm, and the O phase was reduced from 5 μm to <1 μm as the NbC addition increased from 0 wt% to 5 wt%. Mechanical properties illustrated that the coating with the NbC addition of 2.5 wt% had the highest microhardness with 575.6 HV_0.2 and the smallest volume loss with 0.66 mm³ due to fine grain strengthening and dispersion strengthening of TiC. Compared to the Ti-6Al-4V substrate, the microhardness was increased by 1.64 times, and the volume loss was reduced to 30 %. Nevertheless, the mechanical properties of the coatings will exhibit a downward trend by adding excessive NbC (5 wt%), and the coarsening of the TiC could be used to explain this slight decrease.