Nanocrystalline zirconium alloys obtained by severe plastic deformation

Abstract

The structure and properties of commercial zirconium alloys Zr-2.5%Nb and Zr-1%Nb-0.3%Fe-1.2%Sn after severe plastic deformation (SPD) by high pressure torsion (HPT) at room-temperature under pressure of 4 GPa to N=5 (revolutions), which corresponds to a true deformation of ϵ ≈ 6, and their thermal stability upon subsequent annealing have been studied. The alloys for HPT were taken in the two states: alloys were quenched from the single-phase β-region and from the two-phase α-β region. The structure formed in the Zr–2.5%Nb and Zr-%Nb-0.3%Fe-1.2%Sn alloys after HPT is characterized by approximately similar nanograin sizes, 35-55 nm and 30–40 nm, respectively. The HPT of the alloys quenched from the two-phase region results in smaller grain sizes compared to those obtained from the alloys quenched from the single-phase region. It is shown that the HPT increases the microhardness of both alloys by a factor of 2.0–2.5. Annealing at 350°C leads to an insignificant grain growth in the nanocrystalline matrix. The increase in hardness of the alloys after HPT remains after annealing at a temperature of 350–400°C.