Microstructure evolution and mechanical properties of LaB₆-modified Ti₂AlNb alloy fabricated by blended elemental powder metallurgy

This study was conducted to evaluate the microstructure evolution of the blended elemental powder metallurgy Ti₂AlNb alloy with a 2.0 wt% LaB₆ addition and the effects of LaB₆ doping on the microstructure and mechanical properties of the alloy. The results showed that the microstructure evolution could be divided into two stages. During the first stage, the reaction between Ti and Al powders was dominant. During the second stage, the Nb-enriched area disappeared gradually and microstructural homogeneity was enhanced with the diffusion of Nb. It was demonstrated that the LaB₆ phase could be transformed into La₂O₃, (Ti, Nb)B and the (Ti, Nb)₃B₂ transition phase in the sintering process. LaB₆ addition inhibited the precipitation of the brittle α₂ phase and refined the microstructure. Compared with the alloy without LaB₆, the Ti₂AlNb alloy with 2 wt% LaB₆ had 31.5% and 38.4% improvements in the fracture strain at 25 °C and 650 °C, respectively, and its yield strength was also increased.