Effect of strain reversal on the dynamic spheroidization of Ti-6Al-4V during hot deformation

The effect of strain-path reversal on the kinetics of dynamic spheroidization during subtransus hot working was determined for Ti-6Al-4V with a colony a structure. Isothermal torsion tests were conducted at a temperature of 815 degreesC and a strain rate of 0.001 s(-1); strain-path reversals were achieved by applying forward and reverse torsion sequentially. The kinetics of spheroidization were measured as a function of the local (macroscopic) strain for monotonic-deformation, reversed-torsion, and double-reversed-torsion tests. Strain-path reversal led to a reduction in the spheroidization kinetics compared with monotonic deformation for a given total strain. The slower rate of dynamic spheroidization associated with strain-path reversals was ascribed to a reduced rate of sub-boundary formation/lower sub-boundary energies, which drive the boundary splitting process, and less sharp alpha/beta interface curvatures, which control the coarsening process that also contributes to spheroidization.