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

Journal Article · Fri May 15 00:00:00 EDT 2015 · Materials Characterization

DOI:https://doi.org/10.1016/J.MATCHAR.2015.03.016· OSTI ID:22476085

Inaekyan, K. ^[1]; Prokoshkin, S. ^[2]; Pushin, V. ^[3]; Dubinskiy, S.; Sheremetyev, V. ^[1]

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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)

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 secondary 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.

• OSTI ID: 22476085
• Journal Information: Materials Characterization, Vol. 103; Other Information: Copyright (c) 2015 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 1044-5803
• Country of Publication: United States
• Language: English

Related Subjects

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