Effect of β recrystallization on the precipitation evolution of primary α phase and the phase transformation inheritance during thermomechanical processing in Ti-55511 alloy

The crystallographic defects introduced after thermal deformation of near-beta Ti-55511 alloy can have an important impact on the precipitation of primary alpha phase (alpha(p)), beta grain evolution and the texture evolution during the subsequent heat treatment. The investigation indicates that the intragranular short-rod alpha(p) precipitated by strain-induced nucleation deviates from Burgers orientation relationship (BOR) by boundary splitting in 0.27-0.64, accompanied by beta ->alpha(p) transformation, which strictly obeys BOR during ST. In addition, the strain and strain rate can modify the alpha(p)-type after deformation. Three main alpha(p) types are Type I: 50-60 degrees/<-12-10>, Type II: 40-50 degrees or 80-90 degrees/<01-10> and Type III: 90-100 degrees/<-27-53>. The phase transformation inheritance occurs after ST based on the variant selection effect, and the alpha(p) varieties are mainly 80-90 degrees/<-12-10> and 80-90 degrees/<01-10>. Furthermore, the density of the deformation texture (000-1) [11-20] is weakened by the new alpha(p) transformation texture (0001) [-1-780] and the recrystallization texture (23-5-3) [11-22], but it is inherited at 1.23. However, the alpha(p) recrystallization texture significantly restrains the occurrence of the deformation texture inheritance phenomenon at 0.001 s(-1). Moreover, the adjacent alpha(p) grains are mainly 60 degrees/<11-20> to each other, while the beta grains around alpha(p) with a relatively high degree of recrystallization are mainly 30-50 degrees/<34x> to each other. The first one of the static sphericalized alpha(p) is partly generated by coarsening, which is derived from the dispersed nucleus alpha(p) precipitated at the trigonal/tetragonal beta sub-boundaries. The second one is by the GB separation mechanism triggered by the formation of alpha/alpha boundaries within the short-bar alpha(p) grain.

Automated summary

The crystallographic defects introduced after thermal deformation of near-beta Ti-55511 alloy have a significant influence on the precipitation of primary alpha phase (alpha(p)), beta grain evolution, and texture evolution during subsequent heat treatment. The study shows that the intragranular short-rod alpha(p) precipitated by strain-induced nucleation deviates from the Burgers orientation relationship (BOR) through boundary splitting, but strictly follows BOR during solidification and transformation. Furthermore, the type of alpha(p) can be modified by strain and strain rate. After solidification, alpha(p) varieties mainly include 80-90 degrees/<-12-10> and 80-90 degrees/<01-10>. The deformation texture density is weakened by the new alpha(p) transformation texture and recrystallization texture, but is partly inherited after solidification. Adjacent alpha(p) grains are mainly oriented at 60 degrees/<11-20>, while beta grains around highly recrystallized alpha(p) are mainly oriented at 30-50 degrees/<34x>. The static sphericalized alpha(p) is partly generated through coarsening and GB separation mechanisms.