Effect of Cooling and Annealing Conditions on the Microstructure, Mechanical and Superelastic Behavior of a Rotary Forged Ti–18Zr–15Nb (at. %) Bar Stock for Spinal Implants

Abstract

In this work, the microstructure, phase state, texture, superelastic and mechanical properties of a Ti–18Zr–15Nb (at. %) shape memory alloy subjected to a combined thermomechanical treatment, including hot rotary forging with either air cooling or water quenching and post-deformation annealing are studied. It was revealed that the main structural component of the deformed and annealed alloy is BCC β-phase. With an increase in the forging temperature from 600 to 700 °C, the average grain size increases from 5.4 to 17.8 µm for the air-cooled specimens and from 3.4 to 14.7 µm for the water-quenched specimens. Annealing at 525 °C after forging at 700 °C with water quenching leads to the formation of a mixed statically and dynamically polygonized substructure of β-phase. In this state, the alloy demonstrates the best combination of functional properties in this study: a Young’s modulus of ~33 GPa, an ultimate tensile strength of ~600 MPa and a superelastic recovery strain of ~3.4%.

Effect of Cold Drawing and Annealing in Thermomechanical Treatment Route on the Microstructure and Functional Properties of Superelastic Ti-Zr-Nb Alloy

“…Moreover, according to these diagrams, the accumulated residual strains ε acc , σ tr , and σ dis were determined (Figure 4). ultimate tensile strength (UTS) were determined as in [17]. Superelastic cycl carried out at RT on the same type of specimens according to the scheme specimen to 1% deformation in the first cycle with a strain increase by 1% i quent cycle for a total strain of 18%".…”

“…A single β-phase state with a favorable {001} β <110> β crystallographic texture provides the highest recovery strains in these alloys [8,11,12]. The most effective tool to control the structural characteristics of these alloys is thermomechanical treatment (TMT) [10][11][12][13][14][15][16][17]. In a number of works [12,17], TMT combining hot/cold rotary forging and post-deformation annealing (PDA), was applied to Ti- (18)(19)Zr- (14)(15)Nb SMAs with the objective of forming a long-length bar stock 3-8 mm in diameter for bone-implant fabrication.…”

“…The most effective tool to control the structural characteristics of these alloys is thermomechanical treatment (TMT) [10][11][12][13][14][15][16][17]. In a number of works [12,17], TMT combining hot/cold rotary forging and post-deformation annealing (PDA), was applied to Ti- (18)(19)Zr- (14)(15)Nb SMAs with the objective of forming a long-length bar stock 3-8 mm in diameter for bone-implant fabrication. It has been shown that the formation of a polygonized dislocation substructure within β-phase grains with an average size of 5-15 µm and a uniform crystallographic texture close to the [001] direction has led to an enhanced combination of the static functional and mechanical properties: relatively high strength (UTS = 635 MPa), low Young's modulus (E < 45 GPa), and high superelastic recovery strain (ε r se = 3.4%) [17].…”

Surface Modification of Biomedical Ti-18Zr-15Nb Alloy by Atomic Layer Deposition and Ag Nanoparticles Decoration

“…Therefore, metastable β-titanium shape-memory alloys (SMA) exhibiting a low Young's modulus have attracted increased attention in recent years [1,2,[10][11][12][13][14][15]. Among these SMAs, the Ti-18Zr-15Nb (at.%) alloy is the most promising due to its excellent superelasticity at human body temperature and large theoretical superelastic recovery strain (5-6%) [16][17][18]. The development of new approaches to surface modification of such alloys is a relevant issue.…”

Effect of High-Pressure Torsion and Annealing on the Structure, Phase Composition, and Microhardness of the Ti-18Zr-15Nb (at. %) Alloy

“…This alloy in the quenched state (after annealing 700–800 °C following by water quenching) is in the state of single BCC β -phase [ 11 ]. In this state, Ti-18Zr-15Nb alloy exhibits low elastic modulus (30–50 GPa) and superior superelasticity [ 12 ]. It was also shown in [ 13 ] that the thermomechanically treated Ti-18Zr-15Nb alloy exhibits the sufficient corrosion resistance and high fatigue life during functional cycling in Hanks’ solution.…”