Journal
ACTA MATERIALIA
Volume 61, Issue 2, Pages 632-642Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2012.10.008
Keywords
Tantalum; Niobium; High-pressure torsion; Dislocations; Grain size
Funding
- Hungarian National Science Foundation OTKA [71594]
- European Union
- European Social Fund [TAMOP 4.2.1./B-09/1/KMR-2010-0003]
- NFN network High Performance Bulk Nanocrystalline Materials of the Austrian Science Fund [S 10403, S 104]
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Niobium and tantalum are two body centered cubic metals with very different elastic anisotropy. The A(z) = 2 x c(44)/(c(11)-c(12)) constant for Nb and Ta is 0.51 and 1.58, respectively. The submicron grain-size state of the two refractory metals was produced by the method of high-pressure torsion with different pressure values of 2 and 4 GPa for Nb, and 4 and 8 GPa for Ta, and two different deformations of 0.25 and 1.5 rotations, respectively, with equivalent strains of up to similar to 40. The dislocation density and the grain size were determined by high-resolution diffraction peak-profile analysis. The beam size on the specimen surface was 0.2 x 1 mm, allowing the sub-structure along the radius of the specimen to be characterized. The strength of the two metals was correlated with the dislocation density and the grain size. It is found that, though the grain size is well below 100 nm, the role of dislocations in the flow stress of these two metals is significantly greater than that of the grain size. (c) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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