Microstructure and properties of superelastic Ti-18Zr-15Nb alloy subjected to combination of moderate/severe cold drawing and post-deformation annealing

• Published in: Journal of alloys and compounds 2025-01, Vol.1010, p.177370, Article 177370
• Main Authors: Muradyan, A., Lukashevich, K., Derkach, M., Andreev, V., Cheverikin, V., Prokoshkin, S., Sheremetyev, V.
• Format: Article
• Language: English
• Subjects: Cold drawing; Crystallographic texture; Functional properties; Mechanical properties; Microstructure; Shape memory alloys; Titanium alloys
• ISSN: 0925-8388
• DOI: 10.1016/j.jallcom.2024.177370

Ti-18Zr-15Nb (at%) shape memory alloy was subjected to a thermomechanical treatment (TMT), combining cold drawing (CD) with moderate (e = 0.5/1.1), and severe (e = 1.9/3.3) true strains, and post-deformation annealing (PDA) at 500–600 °C to fabricate a wire for medical application. The phase composition, microstructure, crystallographic texture, mechanical and functional properties were studied. The combination of cold drawing with true strain e = 0.5 and PDA at 550 °C for 5 min showed remnants of the original deformed grains, inside of which there is apparently a polygonized substructure, and a partially recrystallized structure of β-phase with a low amount of α-phase (grain size of D≈8 μm). With an increase in true strain, annealing temperature and holding time, a fully recrystallized structure and grain growth were observed. After TMT including the moderate cold drawing, a crystallographic texture with preferable orientation in the β direction was formed. As true strain increases to e = 1.9/3.3, the preferable orientation changes to the β direction; the intensity of this crystallographic texture increases as the true strain increases. Maximum difference between the dislocation and transformation yield stresses was observed after CD with true strain e = 1.1 and PDA at 550 °C for 30 min (Δσ ≈ 405 MPa). Elongation to failure about 20 % was observed after CD with a true strain of e = 0.5 and PDА at 600 °C for 30 min (D≈15 μm). During superelastic cyclic testing with 4 % applied strain after CD (e = 1.9–3.3) and PDA at 550 °C for 5–15 min (D≈1–3 μm) the alloy exhibits high values of superelastic (εrse ≈ 1,8–2,1 %) and total elastic+superelastic (εrel+se ≈ 3,3–3,5 %) recovery strains as well as sufficient maximum tensile stress (σmax ≈ 441–472 MPa), and accumulated residual strain (εacc ≈ 0.4–0.7 %). •Ti-18Zr-15Nb was subjected to moderate and severe cold drawing.•Severe cold drawing forms strong crystallographic texture with a maximum in β direction.•The highest superelastic recovery strain ∼3.1 % and total recovery strain ∼5.4 % are obtained.