• Orozco-Caballero, Alberto
• Atkinson, Michael
• Ojos, Daniel Esque-De Los
• Li, Feng
• Quinta Da Fonseca, João

Abstract

Single phase α-titanium shows anomalous warm deformation behaviour. As the temperature increases, ductility increases in uniaxial tension and decreases in biaxial stretching. Previously, this behaviour was attributed to an increase in strain rate sensitivity and a decrease in twinning activity with temperature. In this study, we show that it can instead be explained by an increase in slip anisotropy with temperature. Grade 2 CP-Ti sheet was tested in uniaxial tension at 20 °C and 300 °C to determine ductility, work hardening behaviour and the coefficient of plastic anisotropy (R-value). The increase in uniaxial ductility with temperature was found to be a consequence of an increasing rate of saturation work hardening with temperature. In the absence of significant twinning, this unexpected work hardening behaviour was attributed to an increase in slip anisotropy with temperature. This hypothesis was supported by crystal plasticity finite element modelling results, which are also able to predict the observed increase in surface roughness with temperature. The increase in anisotropy leads to higher strain localization which, coupled with the increasing work hardening rate helps explain why biaxial ductility decreases with increasing temperature. In addition to explaining the limitations in warm forming of Ti, understanding the origins of these effects contributes to our general understanding of the deformation of other hexagonal metals like Zr and Mg.

Topics

• surface
• polymer
• phase
• titanium
• forming
• plasticity
• ductility
• crystal plasticity