Deformation twinning in Ti-6Al-4V during low strain rate deformation to moderate strains at room temperature

This study examines the possibility of twinning to occur in Ti-6Al-4V during moderate (4 - 14%) uniaxial compression at room temperature using a slow strain rate (10^-6s^-1). To do this, the starting material was manufactured to have strong basal texture components in the transverse and normal directions but not in the rolling direction. After only 6% compressive deformation parallel to the rolling direction it was possible to indentify a significant texture change introducing a strong basal texture component in the rolling direction. TEM analysis provided evidence of twins within grains, but at too low a volume fraction to explain the texture changes. Detailed EBSD mapping was carried out and showed an increasing number of entire grains to have their c-axis aligned with the loading direction in the deformed material, suggestive of entire grain twinning. The root cause for sudden complete grain twinning can only be speculated about at the moment, but it is suggested that the stress required for twin nucleation is significantly higher than that required for their propagation.