Microstructures and mechanical properties of ultrafine-grained Ti foil processed by equal-channel angular pressing and c
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Y.R. Kolobov and G.P. Grabovetskaya Institute of Strength Physics and Materials Science, Siberian Branch of Russian Academy of Sciences, 2/1, Akademicheskaya, Tomsk 634021, Russia
V.V. Stolyarov Institute of Physics of Advanced Materials, Ufa State Aviation Technical University, Ufa 450000, Russia
N.V. Girsova Institute of Strength Physics and Materials Science, Siberian Branch of Russian Academy of Sciences, 2/1, Akademicheskaya, Tomsk 634021, Russia
R.Z. Valiev Institute of Physics of Advanced Materials, Ufa State Aviation Technical University, Ufa 450000, Russia (Received 21 November 2002; accepted 4 February 2003)
We processed coarse-grained Ti and equal-channel angular pressing (ECAP) processed ultrafine-grained (UFG) Ti into 20-m-thick Ti foils by cold rolling and intermediate annealing. The foils produced from rolling the UFG Ti exhibit a homogeneous nanostructure, while foils produced from rolling the coarse-grained Ti exhibit heterogeneous structures with a mixture of nanostructured regions and coarse-grained regions. The former foils also have higher strength and ductility and exhibit uniform deformation over a larger strain range at room temperature than the latter ones. This work demonstrated the advantage and viability of producing nanostructured Ti foil by rolling ECAP-processed UFG Ti stock.
I. INTRODUCTION
Ti is corrosion resistant and biocompatible with human tissues, and therefore, has been used to make various medical implants and devices.1–5 High-strength Ti foils are desired for making medical devices such as hearing aids. Traditionally, Ti foils are manufactured by repetitive cold rolling of Ti sheets with intermediate recrystallization at 650–700 °C to remove strain hardening. As a result, the strength of Ti foil does not increase significantly with cold rolling. Extremely high rolling strain (reduction in thickness) is usually needed to produce metal foils from their much thicker sheet stocks. For example, to produce a 20-m-thick foil from a 1-mmthick sheet, a reduction in thickness of 98% is required. Work hardening from the cold rolling prevents the work piece from being cold rolled to such high strain without intermediate annealing. It is highly desirable that a metal has high ductility so that it can be cold rolled for a large plastic strain before it is necessary to be annealed. J. Mater. Res., Vol. 18, No. 4, Apr 2003
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Plastic deformations by conventional techniques such as rolling, extrusion, and drawing often increase the strength of the metals and alloys but decrease their ductility.6–9 In contrast, severe plastic deformation techniques, such as equal channel angular pressing (ECAP) and high-pressure torsion, can increase the strength of metals and alloys while maintaining good ductility.6,10–17 It has also been reported that materials processed by severe plastic deformation (SPD) have enhanced superplasticity at low temperature and high strain rate.18–24 These remarkable properties are associated with the unique ultraf
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