Effect of microstructure on deformation behavior of Ti–6Al–4V alloy during compressing process

In order to obtain a more quantitative understanding of the formability of Ti–6Al–4V alloys related to different initial microstructures, hot compression tests were conducted on alloys with three different initial microstructures, and Ti–6Al–4V alloy forging process for production of gear reverse idle was also studied. Three different microstructures were first established by combinations of several heat treatments for the first time. Average cooling rate obviously affects α lamellar spacing but does not strongly affect colony size. Measured flow curves for Ti–6Al–4V alloy exhibited peak flow stresses at relative low strains followed flow softening. For a given temperature and strain rate microstructures with finer lamellar spacing exhibited higher flow stresses. Flow curves for different colony sizes were almost coincident. It is concluded that α lamellar spacing strongly affects flow stress but the effect of colony size on flow stress is weak. Deformation resistances for different microstructures were predicted under various deformation conditions using hyperbolic sine law. The predicted constitutive functions coincided well with the results of hot compression tests. Dynamic recovery, dynamic recrystallization and breakage of lamellar structures result in finer microstructures and flow softening during hot forging processing. Cracks were likely to form with coarser lamellar spacing samples at lower forging temperatures.