Microstructural evolution in high Nb containing TiAl alloys by reactive hot pressing
(1.State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China;2.State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China)
Abstract: High Nb containing TiAl alloys with nominal composition of Ti-45Al-9(Nb, W, B) were fabricated at different hot pressing temperatures. The experimental results show that the microstructure of alloys hot pressed at 1 300 ℃ is inhomogeneous, for lots of particulate substances containing Ti3Al phase and Nb powders dispersed in TiAl phase matrix. At 1 350 ℃, only a few lamellar colonies form and the diffusion of Nb element is incomplete. With the increase of hot pressing temperature, the microstructure will be more homogeneous. However, borides appear at higher sintering temperature. Meanwhile, the microstructure becomes coarse at 1 500 ℃. 1 400 ℃ will be an appropriate hot pressing temperature for reaction synthesis of high Nb containing TiAl alloys consisting of fully lamellar (FL) microstructure with the colony size of 30？80 μm. Nb element dissolves into the Ti-Al matrix by diffusion. Pore nests form in situ after Nb powders diffusion.
Key words: titanium aluminides; powder metallurgy; microstructure