Nanostructural analysis of welded Ti-6Al-4V by linear friction welding applied for blisk assemblies

Two Ti-6Al-4V (wt%) alloys have been welded using linear friction welding (LFW), and the microstructural change has been identified using electron backscatter diffraction and site-specific examination using focused ion beam with transmission electron microscopy. In the LFWed sample, weld zone (WZ), thermomechanically affected zone (TMAZ), heat affected zone (HAZ) and parent material occur. In the WZ, the microstructures are deformed, while in the TMAZ, locally built up weak strains remain due to the plastic deformation. Textures are locally formed in the WZ and TMAZ, so called a transverse texture {10 (1) over bar0}< 11 (2) over bar0 >. Such local texture is further accommodated in the HAZ. In the adjacent weld interface, fine {11 (2) over bar2} twinning, alpha', alpha and beta phases coexist in a colony microstructure. There is no elemental segregation to the fine {11 (2) over bar2} twinning and alpha phase, but V is segregated to the twin and twin/alpha boundaries. At the interface, thin beta layers appear due to the V segregation. The {11 (2) over bar2} twinning and thin beta layers meet the Bergers relationship; {011}(beta)//(0001)(alpha) and [11 (1) over bar](beta)//[1 (2) over bar 10](alpha), and the morphology of the twinning is a needle shape whose longitudinal direction is parallel to the c axis of the hcp structure.