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

The evolution of equiaxed primary a phase (alpha(p)) during post-deformation heat treatment of near-alpha 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 degrees C and subsequently heat treatment at 1024 degrees C for times ranging from 0.5 to 24 h. The recrystallization behavior and boundary splitting within equiaxed ap were analyzed by crystallo-graphic orientation and microstructure observations. The results showed that the formation of internal (sub) boundaries within the alpha(p) was by the strong recovery. In most cases, it is difficult to obtain a refinement of big equiaxed alpha(p) by boundary splitting and ap grains were still contiguous with "peanut" shape at relatively short heat treatment time (<= 24 h, 1024 degrees C). The groove in the "peanut" structure was indicative of boundary of alpha/alpha. Only in a few cases, when an isolated beta grain can form within the interior ap along the (sub) boundary, refinement of ap 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. (C) 2017 Elsevier B.V. All rights reserved.