Effect of rare-earth element Gd addition on microstructure of TNM-based TiAl alloys

Abstract

The effects of gadolinium (Gd) on the microstructures of Ti-43.5Al-4Nb-1Mo-0.1B-XGd (X = 0, 0.03, 0.06, 0.1 at.%) alloys were systematically studied. The results show that all microstructures of casting alloys are nearly lamellar, nevertheless, the precipitations of Gd2O3 are formed by the combination of Gd atoms with O atoms, playing a role of heterogeneous nuclei refining both lamellar colonies and the lamellar spacing. However, the phase transition pathways of all alloys were L → L + β →β→ α + β → α + β/B2 + γ → α2 + B2 + γ. After heat treatment, the microstructures were nearly lamellar, but the lamellar spacing was refined by Gd2O3.