Utilization of multi directional forging for fabrication of ultrafine-grained pure titanium

Commercial pure (CP) titanium has many applications in biomaterials especially in implants due to its excellent biocompatibility. The major weakness of CP titanium is low strength compared to that of other titanium alloys. One of the methods can be used to increase the strength of CP titanium are severe plastic deformation methods such as multi directional forging (MDF). Therefore, the aim of this research is the improvement of CP titanium strength by grain refinement in MDF process. For this purpose, after one hour annealing at 800°C, the CP titanium was forged by MDF process up to six passes at ambient temperature. Microstructural studies were performed by optical microscope and scanning electron microscope equipped with EBSD. Mechanical properties were also studied by Vickers’ microhardness and tensile tests. The finite element simulation by Abaqus software was also applied to predict the strain distribution during MDF process. The results of microstructural analysis showed that the average grain size decreased significantly after the MDF process and increasing the pass numbers of MDF led to an increase in grain refinement. After six passes of the MDF process, the average grain size decreased from 45 microns to 390 nm. Mechanical properties results showed that the strength and hardness of specimens increased with MDF process and increasing the number of passes. The hardness and strength of six passes MDFed specimen was about 2 times greater than those of annealed specimen. The strain distribution results obtained from the simulation showed good agreement with experimental results of microhardness distribution.