Evolution of equiaxed alpha phase during heat treatment in a near alpha titanium alloy

- The formation of internal (sub)boundaries within the αp was by the strong recovery.
- The high angle boundary can be inferred by the groove of “peanut” structure.
- At short heat treatment time, it is difficult to obtain a refinement of equiaxed αp.
- Refinement can be readily achieved by the nucleation of β phase within the αp.

The evolution of equiaxed primary α phase (αp) during post-deformation heat treatment of near-α titanium alloy Ti-5.6Al-3.8Sn-3.2Zr-1.0Ta-0.5Mo-0.4Nb-0.35Si was studied. This alloy was isothermally compressed at 1019 °C and subsequently heat treatment at 1024 °C for times ranging from 0.5 to 24 h. The recrystallization behavior and boundary splitting within equiaxed αp were analyzed by crystallographic orientation and microstructure observations. The results showed that the formation of internal (sub)boundaries within the αp was by the strong recovery. In most cases, it is difficult to obtain a refinement of big equiaxed αp by boundary splitting and αp grains were still contiguous with “peanut” shape at relatively short heat treatment time (≤24 h, 1024 °C). The groove in the “peanut” structure was indicative of boundary of α/α. Only in a few cases, when an isolated β grain can form within the interior αp along the (sub)boundary, refinement of αp grain may be achieved due to the obvious reduction of boundary splitting distance. These observations were rationalized on the basis of the classical Mullins grooving analysis.

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