Microstructure and phase stability of TiAl–W ternary alloy

This paper discusses microstructure control of a TiAl–W ternary alloy with emphasis on the phase stability. As a necessary prerequisite for study of the phase stability in the present study, uniformity of the samples is assured by using a well homogenized Ti–W master alloy and breaking down cast structure through thermomechanical processing. The sample, Ti–47Al–3W (at.%) alloy, is prepared by isothermal forging with a reduction of 70% in a temperature range between 1373 and 1573 K, in order to form a fine γ+β micro duplex structure similar to the TiAl–Cr system having good superplastic forming and diffusion bonding ability. Water quenching from 1473 K produces a γ+β+α2 phase in the TiAl–W system and a γ+α2 binary phase in the TiAl–Cr system. Tungsten is enriched in the β phase and the volume fraction of β phase is significantly higher in the TiAl–W than the TiAl–Cr ternary system, suggesting that stronger β stabilization is achieved by W alloying than Cr alloying.