Microstructure evolution and mechanical behaviour of severely deformed pure titanium through multi directional forging

Abstract

Multi directional forging (MDF) is one of the severe plastic deformation methods utilized for production of ultrafine grained materials with improved mechanical properties. The main goal of the current study is to enhance mechanical properties of commercial pure (CP) titanium using grain refinement by MDF method. For this purpose, after one hour annealing at 800 °C, the CP titanium was forged by MDF process up to six passes at room and 220 °C temperatures. The results of microstructure analysis by scanning electron microscope equipped with EBSD showed that average grain size of samples after six MDF passes at room and 220 °C temperatures was about 60 times finer than that of the annealed specimen. The mean grain size of the titanium is reduced from 64 μm to 1 μm after 6 passes at room temperature. Also, the tensile and shear strengths are notably improved by increasing number of MDF passes and reduction of the processing temperature. Yield tensile and shear strengths of six passes MDFed samples at room temperature were about 2.5 times greater than those of the annealed specimen. The correlation between tensile and shear strengths was studied as well. The ratio between yield tensile and shear strengths and also between ultimate tensile and shear strengths was achieved about 1.5 and 2, respectively.