Deformation Behavior and Flow Stress Determination During Two-Stage High Shear-Strain Processing of Titanium at Ambient Temperature

This study presents a two-stage high shear-strain processing deformation technology, consisting of the intensive plastic deformation method of rotary swaging (RS), in combination with the severe plastic deformation method of continuous equal channel angular pressing (ECAP-Conform). The designed technology is experimentally tested at 25 °C, using a commercially pure titanium. Before each individual processing step, uniaxial compression testing is used to acquire stress–strain datasets to subsequently calculate the Hensel–Spittel rheology laws for both of the processing steps. These rheology models are further used to assemble Finite Element Analyses to numerically examine the stress–strain development within the studied material. The study also investigates and characterizes selected deformation parameters. Further, the predicted results are then put in correlation with the experimentally observed (sub)substructure development. The study documents that pre-processing via two passes of rotary swaging has highly positive effects on the substructure development and microstructure homogenization within the titanium workpiece, when compared to a workpiece subjected to just a single pass of ECAP-Conform. The unprocessed Ti and the Ti subjected to RS and ECAP-Conform exhibited faster work-hardening and higher flow stress than the Ti subjected solely to RS. The results also show that the two-stage high shear-strain processed titanium exhibited significantly higher homogeneity of distribution of the imposed strain than a conventional titanium subjected solely to ECAP-Conform. As confirmed by the numerical analyses, the nature of the material plastic flow during RS affected positively the homogeneity after ECAP-Conform.