A TWO STEP SPD PROCESSING OF ULTRAFINE-GRAINED TITANIUM

Equal channel angular pressing (ECAP) and high pressure torsion (HPT) are two severe plastic deformation (SPD) processes that have been used to process ultrafine-grained (UFG) materials. In this investigation, we have attempted to combine these two processes to refine the grain size of coarse-grained pure titanium. ECAP processing was first carried out at 500-450 °C to refine the grain size to about 300 nm. Further processing by HPT resulted in finer grain size and higher dislocation density. The second step, HPT processing, also increased the microhardness, ultimate strength, yielding strength and ductility of the UFG pure titanium.