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.
- A. Titanium aluminides, based on TiAl
- B. Phase diagram
- D. Microstructure