Precipitates in high-Nb TiAl alloyed with Si

The precipitated silicide phase in a high-Nb TiAl alloyed with Si addition was studied. Unlike the Ti5Si3 precipitates formed in Ti-Al-Si ternary system, the silicide particles formed in this study consisted of a Nb5Si3 (designated as ε) phase and had a hexagonal D88 crystal structure. The volume fraction of Nb5Si3 phase increased after heat treatment at 1473 K for 30 min as the B2 phase decomposed. A large number of Nb5Si3 precipitated on lamellar boundaries and had a specific orientation relationship (OR) with α2 and γ: (1 1¯ 0 0)ε//(1 1¯ 0 0)α2 and [1 1 2¯ 3]ε//[1 1 2¯ 0]α2; (1 1¯ 0 0)ε//(11¯2¯)γ and [1 1 2¯ 3]ε//[1 1 0]γ. The semi-coherent interfaces of Nb5Si3 with the matrix resulted in regular interface dislocations.