The significant impact of grain refiner on γ-TiAl intermetallic fabricated by laser-based additive manufacturing

Abstract

Intermetallic γ-TiAl alloy has been considered as a promising structural material for high temperature use, owing to their advantages such as low density, high creep strength and good toughness. However, due to its intrinsic brittleness, γ-TiAl alloy could not accommodate the high thermal stress generated by fast cooling during laser-based additive manufacturing (LAM) process, resulting in cracking and distortion. To surmount the roadblock of low processability associated with γ-TiAl alloy, grain refinement technology was integrated to LAM. In the present work, LaB 6 nanoparticles were identified and experimentally verified, for the first time, as an effective inoculant for LAMed γ-TiAl alloy. The results showed that the grain size of the as-printed alloy drastically decreased from 39.81 ± 9.12 µm to 1.5 ± 2.07 µm through 0.5 wt% LaB 6 addition. Accordingly, the microstructural morphology transformed from coarse near-lamellar colonies into equiaxed and fine grains. The LaB 6 inoculation treatment not only led to the fabrication of crack-free alloy but concurrently increases in compressive yield strength, ultimate strength and strain to fracture by 29%, 12.4% and 61.9%, respectively. Such an enhanced performance is comparable with or even better than the γ-TiAl alloys produced using conventional processing techniques.