Influence of grain boundary state on electrical resistivity of ultrafine grained aluminium

Abstract

An ultrafine grained (UFG) structure has been obtained in commercial purity Al by high-pressure torsion (HPT). Changes in microhardness and electrical resistivity of the UFG material after annealing at various temperatures within a range of 363–673 K have been investigated in correlation with the microstructure evolution. It has been shown that annealing at 363 K leads to substantial decrease in the electrical resistivity while keeping high microhardness level and approximately the same average grain size. The contributions from the various microstructural units (vacancies, dislocations, grain boundaries (GBs)) to the electrical resistivity were analysed. It was shown for the first time that a non-equilibrium state associated with strain-distorted grain boundary (GB) structure strongly affects electrical resistivity of UFG Al. The resistivity of non-equilibrium GBs in UFG structure formed by HPT was evaluated to be at least 50% higher than the resistivity of the thermally equilibrium GBs in a coarse-grained structure.

Keywords:

• Severe plastic deformation
• aluminium
• ultrafine grained structure
• non-equilibrium grain boundaries
• electrical resistivity
• microhardness

Acknowledgements

The X-ray diffraction measurements were performed on equipment at the Resource Center of the Research Park of the St. Petersburg State University ‘Centre for X-ray Diffraction Studies’.

EBSD measurements were performed on equipment at the Interdisciplinary Resource Center for Nanotechnology of the Research Park of the St. Petersburg State University.

Funding

M.Yu.M. and R.Z.V. acknowledge the support of the Ministry of Education and Science of the Russian Federation [Contract No. 14.B25.31.0017].