Structure, phase composition and mechanical properties in bioinert zirconium-based alloy after severe plastic deformation

Abstract

Bioinert binary Zr-1Nb alloy as a perspective material in multi-applicable implant production is investigated. Annealed alloy billets are exposed to severe plastic deformation including multi-cycle abc-pressing and multipass rolling in grooved rollers. The first abc-pressing stage involves three cycles within the temperature interval of 500-400°C from one pressing cycle to another. In the second stage the billets are deformed through rolling in grooved rollers at room temperature. Rolling in grooved rollers provides the formation of a homogeneous structure throughout the bulk billet volume and additional grain refinement. The fine-grained structured alloy embraces 2.8 µm α-Zr equiaxial matrix grains and 0.4 µm β-Nb particles distributed on the boundaries and within α-Zr matrix grain body. As a result of severe plastic deformation binary ultrafine-grained structured alloy with 0.22 µm structural elements is formed. Transmission electron microscopy shows that the microstructure consists of α-Zr grains, while β-Nb phase grains are not identified structurally or via X-ray diffraction. Only the diffraction identification analysis reveals β-Nb presence in the alloy. Ultrafine-grained alloy structure enhances high mechanical properties (yield strength – 450 MPa, ultimate tensile strength –780 MPa, microhardness – 2800 MPa) with low elastic modulus. Zr-1Nb alloy in fine-grained state has elastic modulus of 59 GPa and in ultrafine-grained state – 51 GPa, which are comparable with the elastic modulus of bone tissue (5-50 GPa).