Blocky α phase in β forging TC17 titanium alloy

Abstract

The optical microscope, scanning electron microscope, electron backscattered diffraction and three-dimensional atom probe techniques were employed to investigate the morphology, distributions of alloy elements and orientation of blocky α phase in β forging TC17 titanium alloy. The results show that the blocky α phases are distributed nearby the grain boundary, inside the prior β grains and recrystallized grains, while abnormal microstructure such as long and coarse α lamellar can also be observed inside the grains. There is no significant difference in the distribution of main elements between all kinds of abnormal α and β matrix phase. Therefore, the segregation of alloy composition does not cause the blocky α phase. The acicular α phase is randomly distributed in the grain and is acicular or cotton-blocky under the microscope. In addition, the orientation of α phase is also a main factor determining lamellar morphology. Coarse lamellar and agglomerate blocky α phase can be observed inside the fine recrystallized grains and slightly deformed grains. The fine recrystallized grains represent the undeformed or slightly deformed grains, which grain boundary α and α platelets inside the grain are basically single in orientation. Therefore, the α phase with the same orientation is easy to agglomerate under slow cooling. In addition to the dispersed cotton-blocky α phase, it also appears as blocky α phase which run through the entire grain or agglomerate near the grain boundary.

Keywords

• β forging
• tc17 titanium alloy
• blocky α phase
• three-dimensional atom probe