Study of vacancy-type defects by positron annihilation in ultrafine-grained aluminum severely deformed at room and cryogenic temperatures

Commercial-purity aluminum was processed by equal-channel angular pressing (ECAP) at room temperature (RT-ECAP) and cryogenic temperature (CT-ECAP) with liquid nitrogen cooling between two successive passes. It was found that the RT-ECAPed samples showed equiaxed microstructure after 4 and 8 ECAP pa...

Full description

Saved in:
Bibliographic Details
Published in:Acta materialia 2012-06, Vol.60 (10), p.4218-4228
Main Authors: Su, L.H., Lu, C., He, L.Z., Zhang, L.C., Guagliardo, P., Tieu, A.K., Samarin, S.N., Williams, J.F., Li, H.J.
Format: Article
Language:English
Subjects:
Aluminum
Applied sciences
Cryogenic temperature
Crystal defects
Deformation
Divacancies
Equal channel angular pressing
Equal-channel angular pressing (ECAP)
Exact sciences and technology
Hardness
Lattice vacancies
Low-temperature deformation
Metals. Metallurgy
Positron annihilation (PAL)
Vacancies
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Commercial-purity aluminum was processed by equal-channel angular pressing (ECAP) at room temperature (RT-ECAP) and cryogenic temperature (CT-ECAP) with liquid nitrogen cooling between two successive passes. It was found that the RT-ECAPed samples showed equiaxed microstructure after 4 and 8 ECAP passes, while the CT-ECAPed samples displayed slightly elongated microstructure and slightly smaller grain size. Moreover, the CT-ECAPed samples had higher hardness values than the RT-ECAPed samples subjected to the same amount of deformation. Positron annihilation lifetime spectroscopy (PALS) was used to investigate the evolution of vacancy-type defects during the ECAP deformation process. The results showed that three types of defects existed in the ECAPed samples: vacancies associated with dislocations, bulk monovacancies and bulk divacancies. The CT-ECAPed samples had a higher fraction of monovacancies and divacancies. These two types of defects are the major vacancy-type defects that can work as dislocation pinning centers and induce hardening, resulting in higher hardness values in the CT-ECAPed samples. A quantitative relationship between material hardness and the defect concentration and defect diffusion coefficient has been established.
ISSN:1359-6454
1873-2453
DOI:10.1016/j.actamat.2012.04.003