Microstructure-strength relationship of ultrafine-grained titanium manufactured by unconventional severe plastic deformation process

Abstract With regard to medical applications, the need for producing high-strength titanium-based materials continues to rise due to the fact that pure titanium is characterized by low mechanical properties, yet remarkable corrosion resistance and biocompatibility. Microstructure-strength relationship for pure titanium (grade 2) fabricated by hydrostatic extrusion, an unconventional severe plastic deformation technique, has been quantified within the present study. X-ray powder diffraction, transmission electron microscopy and electron backscatter diffraction examinations were carried out as well as mechanical behavior was tested in order to find out which of the strengthening mechanisms contribute the most to the overall yield strength of the obtained material. Special emphasis has been put on grain refinement, grain boundary character and a few intragranular characteristics, indicating grain fragmentation. Applying multi-stage hydrostatic extrusion process to pure titanium resulted in fabricating the material that exhibits strong, fiber texture and non-homogeneous, ultrafine-grained microstructure with a host of structural defects in the form of dislocations and low-angle grain boundaries. The material tends to demonstrate remarkable mechanical properties, exceeding those of Ti-6Al-4V, yet its ductility is substantially lower. Based on the microstructure-property analysis it was found that the contribution of grain refinement and substructure evolution to the strength of the hydrostatically extruded titanium was of the highest significance.