Flow stress constitutive relationship between lamellar and equiaxed microstructure during hot deformation of Ti-6Al-4V

Abstract

The mechanical properties of Ti–6Al–4V alloy are very sensitive to its microstructure morphology. Commercially available Ti–6Al–4V was heat treated above and below the β -transition temperature to obtain lamellar and equiaxed morphologies respectively. Hot compression tests up to 60% deformation were carried out on both the morphologies in the temperature range of 750–950 °C and strain rates range of 0.001–10 s−1. The true stress strain curve obtained from the compression tests demonstrates a higher flow softening in the lamellar morphology as compared to the equiaxed morphology of this alloy. This behavior is also observed by the newly defined average flow softening index based on Seller’s constitutive model parameter. A significantly higher hot working activation energy compared to the lattice self-diffusion activation energy of α -Ti indicates the dynamic recrystallization during flow softening. A linear relationship between the flow stress corresponding to the equiaxed and lamellar morphologies was observed. A constitutive relationship between the flow stress of the two morphologies with strain was established and it was observed to obey a power law relation. The flow behavior of these morphologies at different deformation conditions were further characterized using microstructure development after the hot deformation.