Spectral line

Indentation hardness

Spectroscopy

Quantum mechanics

Deformation (meteorology)

Engineering

Metallurgy

Materials science

Severe plastic deformation

Surgery

Grain boundary

Torsion (gastropod)

Positron annihilation

Physics

Astronomy

Positron annihilation spectroscopy

Microstructure

Positron

Condensed matter physics

Composite material

Crystallography

Medicine

Chemistry

Electron

Crystallographic defect

Forensic engineering

Dislocation

Engineering physics

Doppler broadening

MATERIALS TRANSACTIONS

A high density of lattice defects is introduced to materials by severe plastic deformation (SPD). Numerous experimental techniques, in particular electron microscopy, X-ray, electron and neutron diffraction, etc. are employed to characterize the evolution of microstructure and defects with strain introduced to the material by SPD. These techniques concentrate mainly on the investigation of planar (grain boundaries) and line defects (dislocations). On the other hand, point defects, namely vacancies and their agglomerates are investigated in less detail. Positron annihilation spectroscopy (PAS) proved to be an effective method for the investigation of point defects and dislocations in ultra-fine grained (UFG) materials. This study summarizes the results of the investigation of lattice defects in UFG metals with fcc (Al, Ni, Cu), bcc (Fe, Nb, W) and hcp (Mg, Ti) structure prepared by high pressure torsion (HPT). Two techniques of PAS were employed (i) positron lifetime spectroscopy (LT) allowing to characterize the type and concentration ratio of lattice defects in the severely deformed material and (ii) Doppler broadening (DB) of annihilation radiation providing analysis of the homogeneity of the UFG structure and spatial distribution of defects. The latter technique was complemented by mapping of microhardness distribution throughout the surface of the HPT specimens.

The Development of Vacancies during Severe Plastic Deformation