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High-pure nanostructured titanium obtained by cryogenic quasi-hydrostatic extrusion
|Mykhailo Tykhonovskyi 1, Pavel Khaimovich , Igor' Kislyak , Kseniya Kutniy , Vladimir Okovit , Tat'yana Rudycheva|
1. Kharkov Institute of Physics and Technology (KIPT), Akademiskaja 1, Kharkov 61108, Ukraine
Titanium and its alloys are widely used in various fields of engineering and medicine. The requirements for their physical, mechanical and chemical properties are increasing, so we need for a new approaches of controlling of structure and characteristics of these materials. This applies, first of all to the commercially pure titanium and high-pure titanium, for which the possibility of increasing the strength characteristics to a large extent limited. At the same time, for some applications, in particular for manufacture of medical implants pure titanium is most preferable due to the high biocompatibility and its lack of toxic elements. Improving the strength of pure metals, including titanium, up to the strength level of heavily doped alloys is possible by different extreme effects on bulk material. These effects include the severe plastic deformation (SPD) and the low-temperature or cryogenic deformation (CD). Thus, the aim of this study was to investigate the role of the original grain size of iodide titanium obtained by SPD and subsequent annealing on the evolution of its structure and modify its properties after cryogenic deformation by quasi-hydrostatic extrusion.
Using SPD under the scheme of upsetting-extrusion-drawing was obtained the high-pure titanium with the grain size of about 160 nm. The subsequent annealing of titanium at the temperatures of 350-550ºC allowed to create the microstructure with grain sizes from a few hundred nanometers up to 9 mkm. Samples with the different grain sizes were subjected of quasi-hydrostatic extrusion at liquid nitrogen temperature (77 K) and room temperature as described in, and then the microstructure and mechanical properties were investigated.
It is shown that quasi-hydrostatic extrusion leads to effective grain refinement, especially in the conduct of quasi-hydrostatic extrusion at nitrogen temperature. Thus, in titanium with the original grain size of 9 mkm the quasi-hydrostatic extrusion with degree of deformation of 45% leads to the grain refinement in 4 times under the deformation at room temperature and in 20 times in the case of deformation at 77 K. In the samples of submicrocrystalline titanium after quasi-hydrostatic extrusion at room temperature there was some decreasing of the yield strength and microhardness with an appreciable increasing of tensile strength. For samples that were deformed at cryogenic temperature all these parameters increased. In addition, the quasi-hydrostatic extrusion of submicrocrystalline titanium promotes to significant increasing plasticity of the material, in particular, the elongation to failure increased from 6.7% to 12.3%. Thus, the combination of methods of SPD with the cryogenic quasi-hydrostatic extrusion allowed to create a high-pure nanocrystalline titanium with the grain size of 75 nm, high strength (σb = 930 MPa) and plasticity (δ ≈ 12%). This material may be of interest for various applications, in particular for the manufacture of medical implants.
Presentation: Poster at Nano and Advanced Materials Workshop and Fair, by Mykhailo Tykhonovskyi
See On-line Journal of Nano and Advanced Materials Workshop and Fair
Submitted: 2013-06-03 15:23 Revised: 2013-06-07 09:25