Severe plastic deformation (SPD) of titanium at near-ambient temperature

Severe plastic deformation of titanium at near-ambient temperature has been realized using large-strain machining. The material that received the highest levels of strain, the chip, is found to have a nanocrystalline structure with ∼100 nm sized grains. This microstructure is finer than that observed in titanium following equal channel angular pressing at elevated temperatures. The machined surface of the workpiece is found to have a graded microstructure composed of ultrafine grains at and near the surface and a preponderance of twins further into the subsurface. The parameters of the large-strain deformation field, namely strain rate and strain, are obtained using an adaptation of a particle image velocimetry technique. The microstructure characteristics are shown to be a consequence of the deformation field parameters, which activate both twinning and dislocation-mediated mechanisms of plastic flow.