Abstract
The effect of silicon content on the microstructure and phases present in Ti–(20–23)Al–11Nb alloys has been studied in the temperature range 800–1270°C.Four phases, βo, α2, O, and a silicide, are formed. The parent βo is ordered at 1270°C. At 1050°C α2 is formed which exhibits a higher silicon solubility than the parent βo. A peritectoid transformation β0+silicide→α2 is proposed. Assuming that niobium substitutes for titanium and silicon for aluminium, energy dispersive X-ray spectroscopic data suggest that the α2 phase, unlike that in binary Ti–Al alloys, is highly stoichiometric and of the form (Ti+Nb)3(Al+Si). Similarly the silicide corresponds to binary Ti5Si3 with the same site substitution as in the α2 phase. The O phase is orthorhombic and similar in composition to the α2 which it replaces: its formation is promoted by silicon.
MST/3088
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