Characterization of defect microstructure in MgRE (RE=Ce, Nd) alloys after processing by high-pressure torsion using positron annihilation spectroscopy and a high resolution X-ray diffraction

• 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 (DB-VEPAS). 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).

Ämnesord

NATURVETENSKAP  -- Fysik -- Den kondenserade materiens fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Condensed Matter Physics (hsv//eng)

Nyckelord

Dislocations

HPT

Mg

Positron

Rare earth

Spectroscopy

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