Sustainable manufacturing of a high-value tubular Ti-6Al-4V component using flow-forming process; effect of feed-rate on microstructure evolution

Flow-forming is a comparatively sustainable manufacturing process with a potential to produce seamless highvalue tubular components (e.g., actuators and shafts). This paper investigates microstructure evolution and the corresponding deformation mechanisms during warm (i.e., pre-heated to 600 ◦C) flow-forming of Ti–6Al–4V alloy under different feed rates. The increase in the feed-rate, from 1 to 2.5 mm/rev, which results in an increased roller-workpiece contact area, had led to longer final component (i.e., from 53 to 108 mm). EBSD analyses of microstructure suggest the occurrence of dynamic recrystallisation (DRX) in both α and β phases. Elongated α grains were observed in the outer surface, indicative of severe plastic deformation, accommodated by the deformation of the primary α grains and continuous dynamic recrystallisation (CDRX) in β. Analyses of crystallographic texture show the presence of strong B-fiber {1120} < 1100 > shear texture, indicating dominant shear deformation. The calculated Schmid factors for most of the α-grains were greater than 0.4 for the prismatic and pyramidal slip systems, thus indicating the dominant activation of these slip systems during flow-forming. These results elucidate the importance of rate-controlled thermal-mechanical interactions in tailoring the microstructure and manufacturability of titanium components via warm flow-forming.