Structural and phase composition changes of titanium in different initial structural states under shock wave loading
The structural and phase composition changes of a shock-treated coarse-grained, ultrafine-grained and submicrocrystalline commercially pure titanium VT1-0 were studied by methods of transmission and scanning electron microscopy and x-ray diffraction. Titanium samples were subjected to mechanical-thermal processing, including the influence of a developed (megaplastic) plastic deformation and thermal annealing. As a result of this treatment the initial structure of the samples with different grain size in the range from 0.2 to 40 µm is formed. Then titanium samples was loaded using a flyer plate technique and the Kolsky method with the rod of Hopkinson. The metal flyer velocity was in the range of 2–3 km/s and the shock pressure was calculated to be 40 GPa.
It was found that after shock wave impact by a flyer plate technique to pressure 40 GPa the grain size of coarse-grained titanium undergoes to significant reduction. So, for samples with the initial grain size 40 µm the size of the grains decreases in 150 times. The high-pressure experiments on submicrocrystalline titanium samples (with the initial grain size 0.25 ± 0.02 µm) do not show the considerable variation of the grain sizes. The fragmentation of grain structure is observed only in samples with an average grain size greater than 0.3 µm. The same structural changes were observed after shock wave loading by the Kolsky method with the rod of Hopkinson.
X-Ray diffraction analysis and electron microdiffraction reveal the presence of a new ω-phase in the investigated samples as the result of phase transformation α→ω at high pressures.