Composition: Ti-6%Al-4%V.

Processing: As-received.

Etching: 30-120s acid mixture (HCl+HF+HNO₃).

The microstructure reveals deformed grains of α phase (white) together with untransformed β phase of angular shape at the triple junctions. The etchant does not reveal very well the α/α grain boundaries. This microstructure is obtained by a recrystallization anneal from an alloy that was previously homogenized and rolled. Annealing is carried out slightly below β_transus (999ºC). Slow cooling (50-55ºC/h) until ~760ºC followed by air cooling results in coarsening of the α phase without formation of lamellar α within the grains of β phase. This treatment produces relatively large α grains (~5 µm). A smaller grain size, down to ~2 µm, can be obtained by annealing at lower temperatures (800-850ºC), thus enhancing mechanical properties such as fatigue and yield strength. In this case, rapid cooling is needed after homenizing, which limits the size of the specimen. 

Ti6Al-V diagram

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