Quasi-in-situ investigation on complete lamellar fragmentation of ,B-solidified TiAl alloy during uniaxial isothermal compression

The coarse as-cast lamellar microstructure in TiAl alloys is difficult to be broken completely by thermomechanical processing. Some remnant lamellar colonies in the deformed microstructure seriously affect the microstructural homogeneity and deteriorate the properties. In this study, it is found that by isothermal compression at 1230 degrees C and 1250 degrees C, the lamellar colonies of Ti-43.5Al-4Nb-1Mo-0.1B (TNM) alloys can be completely broken. This is attributed to the weakened anisotropic deformation behavior of the lamellar colonies due to the isothermal holding treatment before deformation. The deformation behavior at 1230 degrees C was investigated by quasi-in-situ experiments. It is observed that the regions near lamellar colony boundaries first undergo dynamic recrystallization at small strain, while the lamellar colonies gradually break down with increasing strain. The adequate fragmentation of lamellar colonies mainly depends on the recrystallization of alpha lamellae ( alpha L ). The isothermal holding at 1230 degrees C leads to an increase in the content and thickness of alpha L , which allows it to assume more deformation and promotes its recrystallization by reaching critical strain. The interrupted gamma lamellae ( gamma L ) formed by decomposition during isothermal holding facilitates the occurrence of alpha recrystallization within the lamellar colonies by hindering dislocation movement. In addition, recrystallized gamma grains ( gamma R ) are gradually dissolved by the formation of alpha precipitates inside them through the gamma -> alpha phase transformation and the subsequent consumption of alpha precipitates by the recrystallized alpha grains. (c) 2024 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.