Microstructure and mechanical properties of highly deformed Ti–6Al–4V

Several forming processes, β extrusion, α + β extrusion, rotary piercing, and flowforming, were utilized to produce seamless Ti–6Al–4V tubes. The β-extruded and rotary-pierced tube materials displayed similar microstructures showing a coarse prior β grain size. Microstructure of the α + β extruded material, on the other hand, consisted of a fine microstructure showing severely elongated primary α and transformed β phases. The flowformed materials, having gone through an extreme cold work, displayed the finest microstructure consisting of severely elongated α and β phases. TEM study on a flowformed sample further verified severe deformation through observed very fine grains with high dislocation densities. The flowformed tube material provided the highest tensile strength among all the tubes, with an ultimate tensile strength (UTS) greater than 1100 MPa. Similarly, when tested for fatigue, the flowformed material had a slight advantage over the other material variants. The α + β extruded material appeared to have the second longest fatigue life after the flowformed material.