Effect of severe plastic deformation by high-pressure torsion at different temperatures and subsequent annealing on structural and phase transformations in Zr-2.5% Nb alloy

• Published in: Journal of alloys and compounds 2021-06, Vol.865, p.158874, Article 158874
• Main Authors: Rogachev, S.O., Sundeev, R.V., Nikulin, S.A.
• Format: Article
• Language: English
• Subjects: Annealing; Crystal defects; Crystallites; Deformation effects; Grain growth; Grain structure; High-pressure torsion; Inhomogeneity; Metals and alloys; Microhardness; Microstructure; Niobium base alloys; Phase transitions; Plastic deformation; Room temperature; Temperature; Thermal stability; Transmission electron microscopy, TEM; X-ray diffraction; Zirconium alloys; Zirconium base alloys
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2021.158874

•The Zr-2.5% Nb alloy was processed by HPT in the temperature range from RT to 325 °С.•HPT leads to the grain refinement and to the α-Zr → ω-Zr phase transformation.•The microstructure of the Zr-alloy after HPT is characterized by significant inhomogeneity.•With an increase in the HPT temperature from RT to 325 °C, the amount of the ω-phase decreases.•With an increase in the HPT temperature from RT to 325 °C, the thermal stability of the ω-phase increases. The effect of the temperature of the high-pressure torsion (HPT) deformation and subsequent annealing in a wide temperature range on the structural and phase transformations in the Zr-2.5% Nb alloy and its microhardness has been studied. In the course of the HPT process, the grain structure in the alloy is refined to the nano- and submicron level, the density of crystal defects increases and the α-Zr → ω-Zr phase transformation occurs, which are accompanied by an increase in the microhardness values. The microstructure of the alloy after HPT is characterized by significant inhomogeneity, and the crystallite size increases slightly with increasing the HPT temperature. Annealing of the HPT-processed alloy samples leads to their softening due to the reverse ω-Zr → α-Zr phase transformation and due to the grain growth. With an increase in the HPT-deformation temperature from room temperature to 325 °C, the amount of the ω-Zr phase in the alloy structure decreases, while its thermal stability increases. The HPT-processed Zr-2.5% Nb alloy has an advantage for medical applications compared to other commercial zirconium alloys.