Influence of shear deformation under pressure at different temperatures on mechanical properties of E125 zirconium alloy

Abstract

The work is devoted to study the effect of shear deformation by highpressure torsion (HPT) at various temperatures, as well as post-deformation annealing on the mechanical properties of an industrial zirconium alloy Zr–2.5% Nb (russian standart E125). The HPT-deformation was carried out using flat samples of the alloy in a recrystallized with a diameter of 20 mm and an initial thickness of 1.5 mm. HPT was performed at room temperature, as well as at temperatures of 300 and 325 oC, using a pressure of 4 GPa and the number of turns of the lower anvil N = 5. As methods for studying the material, we used Vickers microhardness measurement, X-ray phase analysis, and tensile testing of miniature samples cut from the alloy after HPT. It was shown that the greatest hardening of the alloy was observed after HPT at room temperature: the microhardness values increased 2.4–2.5 times (380–400 HV) compared with the initial state of the alloy. Annealing of alloy samples processed by HPT leads to the softening of the material. An increase in the HPT-process temperature enhances the thermal stability of the alloy. The mechanical properties (yield and tensile strength, and relative elongation) of alloy samples after HPT and subsequent annealing are determined. After the HPT-deformation, the alloy samples are characterized by high strength and very low ductility: the failure of the samples under tensile occurs on the elastic area of the stress–strain curve at stresses of 920–1060 MPa. The modes of deformationheattreatment of the alloy providing a combination of high strength and satisfactory ductility are established. For the alloy processed by HPT at a temperature of 325 oС and annealed at a temperature of 400 oС, the offset yield point and tensile strength were 840 and 900 MPa, respectively, and the relative elongation was 4%. The results allows to expand the applicability of zirconium alloys as a material for the manufacture of medical implants and medical instruments.The research was implemented under financial support of the Russian Foundation for Basic Research (RFFI) within the framework of the scientific project No. 20-32-70007.The authors express their gratitude to R. V. Sundeev, Cand. Phys.-Math., for his assistance in conduction of X-ray phase analysis.