Thermal stability of nanocrystalline structure in niobium processed by high pressure torsion at cryogenic temperatures

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2011-01, Vol.528 (3), p.1491-1496
• Main Authors: Popov, V.V., Popova, E.N., Stolbovskiy, A.V., Pilyugin, V.P.
• Format: Article
• Language: English
• Subjects: Cryogenic temperature; Crystallites; Electron microscopy; Grain growth; Grain refinement; High-pressure torsion; Materials science; Microhardness; Nanocrystalline structure; Nanocrystals; Niobium; Recrystallization; Thermal stability; Torsion
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2010.10.052

▶ We achieved grain refinement in Nb up to average grain size of 75nm by high-pressure torsion at cryogenic temperature. ▶ The as-obtained structure possesses the record-breaking microhardness of 4800MPa. ▶ This structure is stable up to 300°C Evolution of structure of Nb subjected to high-pressure torsion (HPT) in liquid nitrogen and further annealing in the temperature range of 100–600°C has been studied by transmission electron microscopy (TEM). HPT at the cryogenic temperature of 80K results in the formation of nanocrystalline structure in Nb, with crystallite sizes of about 75nm and the record-breaking microhardness of 4800MPa. The structure obtained is stable at room temperature but possesses relatively low thermal stability, namely, it undergoes recrystallization at lower temperatures than the structure after the conventional deformation or room-temperature HPT.