• Abib, K.
• Bibimoune, I.
• Liedke, M. O.
• Bradai, D.
• Wagner, A.
• Huang, Yi
• Langdon, T. G.
• Bourezg, Y. I.
• Matěj, Zdeněk

Abstract

Two MgRE (RE=Ce, Nd) alloys with ultrafine-grain (UFG) microstructures were prepared by high-pressure torsion (HPT) at room temperature. The in-depth distribution of defects was characterized by Doppler broadening –variable energy positron annihilation spectroscopy (DBVEPAS). The characteristic S parameter increases in bulk after HPT processing relative to an as-received sample and shows a relative stability between ½ and 10 turns, which suggests a rise in the open volume defect density. However, a theoretical analysis of the S(E) depth profile reveals an increase in the positron diffusion length from ~115 nm for the as-received state to ~207 nm after 10 HPT turns. Almost all the open volume defect consisted of dislocations (positron lifetime of τ = 260 ps). The dislocation density deduced from high-resolution X-ray diffraction in the HPT disc radial direction was reasonably homogeneous (around 4-6 ×1014 m-2).

Topics

• density
• grain
• x-ray diffraction
• positron annihilation lifetime spectroscopy
• dislocation