Evidence for a transition in deformation mechanism in nanocrystalline pure titanium processed by high-pressure torsion |
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| Authors: | Chao Yang Min Song Yong Liu Shima Sabbaghianrad Terence G Langdon |
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| Institution: | 1. State Key Laboratory of Powder Metallurgy, Central South University, Changsha, China;2. Departments of Aerospace &3. Mechanical Engineering and Materials Science, University of Southern California, Los Angeles, CA, USA;4. Materials Research Group, School of Engineering Sciences, University of Southampton, Southampton, UK |
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| Abstract: | Nanocrystalline titanium with an average grain size of about 60–70 nm was prepared by high-pressure torsion. The results of hardness and structural evolutions indicate that a strain-induced hardening–softening–hardening–softening behaviour occurs. For coarse-grained titanium, 〈a〉-type dislocation multiplication, twinning and a high pressure-induced α-to-ω phase transformation play major roles to accommodate deformation, leading to a significant strain hardening. As deformation proceeds, dynamic recrystallisation leads to a decrease in dislocation density, especially for 〈a〉-type dislocations, leading to a slight strain softening. The 〈c〉-component dislocation multiplication dominates the deformation when the grain size decreases to 100 nm and 〈c〉-component dislocation multiplication, grain refinement and the α-to-ω phase transformation contribute to the second strain hardening. The following strain softening is attributed to dynamic recovery. |
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| Keywords: | Nanocrystals deformation mechanisms dislocations transmission electron microscopy high-pressure torsion grain refinement |
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