Microstructure and Mechanical Properties of CP-Ti Processed By Accumulative Roll Bonding and Isolated Shear Rolling

Commercially pure titanium (CP-Ti) was processed by two means to either increase its strength or formability, through controlling the grain size or texture of the material. Warm accumulative roll bonding (ARB) was used in this study to refine the grain size of CP-Ti and ultimately increase its strength. Sheet samples were processed by up to seven consecutive ARB cycles at a selected temperature of 450 ºC, with an overall equivalent strain of 5.6. Mechanical characterization and microstructural examination were carried out on the processed material to track their changes and relationships with regard to one another. TEM revealed significant grain refinement in the material, with submicron microstructure achieved even after one cycle of warm processing. Further processing was shown to progressively fragment the highly elongated grains, ultimately producing a predominantly-equiaxed ultrafine grain structure with an average grain size of ~100 nm. Tensile strength and microhardness of the material increased with the number of ARB cycles; the strength–grain size relationship followed the Hall–Petch equation. On the other hand, an approach for controlling the texture of rolled sheets via isolating the distributed shear strains is introduced and validated. Isolated shear rolling (ISR) was carried out on CP-Ti sheets at 300 °C. After a single pass at ~31% reduction the material developed a highly basal texture and exhibited a higher Lankford value suggesting greater stretch formability. Furthermore, after flash annealing the materials strength and total elongation resembled that of the as-received state, while maintaining the developed basal texture and increased Lankford value.