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Title: Comparative study of structure formation and mechanical behavior of age-hardened Ti–Nb–Zr and Ti–Nb–Ta shape memory alloys

This work sets out to study the peculiar effects of aging treatment on the structure and mechanical behavior of cold-rolled and annealed biomedical Ti–21.8Nb–6.0Zr (TNZ) and Ti–19.7Nb–5.8Ta (TNT) (at.%) shape memory alloys by means of transmission electron microscopy, X-ray diffractometry, functional fatigue and thermomechanical testing techniques. Dissimilar effects of aging treatment on the mechanical behavior of Zr- and Ta-doped alloys are explained by the differences in the ω-phase formation rate, precipitate size, fraction and distribution, and by their effect on the alloys' critical stresses and transformation temperatures. Even short-time aging of the TNZ alloy leads to its drastic embrittlement caused by “overaging”. On the contrary, during aging of the TNT alloy, formation of finely dispersed ω-phase precipitates is gradual and controllable, which makes it possible to finely adjust the TNT alloy functional properties using precipitation hardening mechanisms. To create in this alloy nanosubgrained dislocation substructure containing highly-dispersed coherent nanosized ω-phase precipitates, the following optimum thermomechanical treatment is recommended: cold rolling (true strain 0.37), followed by post-deformation annealing (600 °C, 15–30 min) and age-hardening (300 °C, 30 min) thermal treatments. It is shown that in TNT alloy, pre-transition diffraction effects (diffuse reflections) can “mask” the β-phase substructure and morphology of secondarymore » phases. - Highlights: • TNZ alloy is characterized by much higher ω-phase precipitation rate than TNT alloy. • Difference in precipitation rates is linked to the difference in Zr and Ta diffusion mobility. • Aging of nanosubgrained TNZ alloy worsens its properties irrespective of the aging time. • Aging time of nanosubgrained TNT alloy can be optimized to improve its properties.« less
Authors:
 [1] ;  [1] ;  [2] ;  [3] ; ;  [1] ;  [4]
  1. Ecole de Technologie Superieure, 1100, Notre-Dame Str. West, Montreal Quebec H3C 1K3 (Canada)
  2. National University of Science and Technology “MISIS”, Leninskiy prosp. 4, Moscow 119049 (Russian Federation)
  3. Institute of Metal Physics, Ural Branch of Russian Academy of Sciences, 18, S. Kovalevskoy Str., Ekaterinburg 620199 (Russian Federation)
  4. (Russian Federation)
Publication Date:
OSTI Identifier:
22476085
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Characterization; Journal Volume: 103; Other Information: Copyright (c) 2015 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; AGE HARDENING; ANNEALING; DEFORMATION; DIFFUSION; DISLOCATIONS; MICROSTRUCTURE; NANOSTRUCTURES; NIOBIUM COMPOUNDS; PRECIPITATION; PRECIPITATION HARDENING; ROLLING; SHAPE MEMORY EFFECT; STRESSES; TANTALUM COMPOUNDS; TERNARY ALLOY SYSTEMS; THERMOMECHANICAL TREATMENTS; TITANIUM COMPOUNDS; TRANSMISSION ELECTRON MICROSCOPY; X-RAY DIFFRACTION; ZIRCONIUM COMPOUNDS