TY - JOUR

T1 - Effect of commercial purity levels on the mechanical properties of ultrafine-grained titanium

AU - Purcek, G.

AU - Yapici, G. G.

AU - Karaman, I.

AU - Maier, H. J.

N1 - Funding information: This work was mainly supported by the National Science Foundation – International Materials Institute Program through the grant no. DMR 08-44082 , Office of Specific Programs, Division of Materials Research, Arlington, Virginia. GP would like to acknowledge the support from the Scientific Research Projects of Karadeniz Technical University, Turkey and TUBITAK, Turkey , under 2219-International Postdoctoral Research Scholar Program.

PY - 2010/11/13

Y1 - 2010/11/13

N2 - 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 110μm and 70μm, 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 (σy), 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 σy after eight pass ECAE, from 531 to 758MPa. 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.

AB - 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 110μm and 70μm, 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 (σy), 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 σy after eight pass ECAE, from 531 to 758MPa. 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.

KW - Equal-channel angular extrusion/pressing

KW - Grade-2 and grade-4 CP-Ti

KW - Mechanical properties

KW - Microstructure

KW - Ultrafine-grained materials

UR - http://www.scopus.com/inward/record.url?scp=79151479884&partnerID=8YFLogxK

U2 - 10.1016/j.msea.2010.11.021

DO - 10.1016/j.msea.2010.11.021

M3 - Article

AN - SCOPUS:79151479884

VL - 528

SP - 2303

EP - 2308

JO - Materials Science and Engineering A

JF - Materials Science and Engineering A

SN - 0921-5093

IS - 6

ER -