Browsing by Author "Purcek, G."

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Effect of commercial purity levels on the mechanical properties of ultrafine-grained titanium
(Elsevier, 2011-03-15) Purcek, G.; Yapıcı, Güney Güven; Karaman, I.; Maier, H. J.; Mechanical Engineering; YAPICI, Güney Güven
Two grades of commercial purity (CP) titanium (grades 2 and 4) were processed using equal-channel angular extrusion (ECAE) at 300 ◦C and 450 ◦C, respectively. The processing temperatures were the minimum temperatures at which eight pass ECAE could be performed without any shear-localization. The coarse-grained (CG) microstructures of as-received grade-2 and grade-4 CP-Ti, with average grain sizes of 110_m and 70_m, respectively, were refined down to sub-micron levels with a mean grain size of about 300nm for both grades after 8 ECAE passes. The ultrafine-grained (UFG) microstructures led to substantial enhancement in strength for both grades. The grade-2 sample showed a more than two fold increase in yield strength (_y), from 307MPa for the as-received one to about 620MPa for the processed samples. The grade-4 CP-Ti exhibited a relatively smaller increase in strength due to the higher processing temperature, and it showed about 50% increase in _y after eight pass ECAE, from 531 to 758 MPa. These strength levels were obtained with high ductility levels of 21% and 25% for UFG grade-2 and grade-4 Ti, respectively. These improvements in mechanical properties are attributed to the substantially refined grain size and increased dislocation density. Grade-4 Ti is stronger than grade-2 because of the higher oxygen content. The higher ductility and significantly higher strain hardening capability of UFG grade-4 Ti, in spite of the similar grain size and microstructure with UFG grade-2 Ti, is also due to the higher impurity content, probably resulting in a higher dislocation storage capability during room temperature deformation, and thus, higher strain hardening capacity. Such properties make UFG grade-4 Ti comparable to the commercial Ti–6Al–4V alloy for biomedical applications without negative effects of the alloying elements on biocompatibility.
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Mechanical and wear properties of ultrafine-grained pure Ti produced by multi-pass equal-channel angular extrusion
(Elsevier, 2009-08-20) Purcek, G.; Saray, O.; Kul, O.; Yapıcı, Güney Güven; Haouaoui, M.; Maier, H. J.; Mechanical Engineering; YAPICI, Güney Güven
In this study, pure grade 2 Ti was processed via equal-channel angular extrusion (ECAE) for 8 and 12 passes following route-E at 300 °C. After processing, the microstructural evolution, tensile properties and wear behavior were investigated. ECAE-processed Ti exhibited a significant improvement in strength values with a slight decrease in ductility. However, the wear test results surprisingly showed that the strengthening of titanium by ECAE processing does not lead to the improvement of wear resistance at least for the pressures and sliding distances used in this study. This finding was mainly attributed to the tribochemical reaction leading to oxidative wear with the abrasive effect in Ti. Three distinct regions were formed on the subsurface of CG and UFG Ti after sliding wear, which are the tribolayer including titanium oxide with smeared wear material at the top, a deformed region having material structure oriented along the sliding direction in the middle, and the original unaffected bulk material at the bottom.