Nanostructurization of Nb by high-pressure torsion in liquid nitrogen and the thermal stability of the structure obtained
- 17 March 2012
- journal article
- Published by Pleiades Publishing Ltd in Physics of Metals and Metallography
- Vol. 113 (3), 295-301
- https://doi.org/10.1134/s0031918x1203009x
Abstract
The evolution of the Nb structure upon high-pressure torsion (HPT) in a Bridgeman chamber in liquid nitrogen and a subsequent annealing in the range from 100 to 600°C has been studied by the TEM method. With an increase in the degree of deformation, the structure exhibits three stages of refinement: dislocation cellular structure; mixed structure consisting of cells and subgrains; and submicron or nanocrystalline grain structure. The HPT using 3 and more revolutions of the anvils at 80 K leads to the formation in Nb of a nanocrystalline structure with an average grain size of ∼75 nm and a record high microhardness of 4800 MPa. The structure is stable at room temperature but possesses a relatively low thermal stability, i.e., the recrystallization starts at lower temperatures than it does after conventional deformation or an HPT at room temperature.Keywords
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