The University of Southampton
Engineering

Research project: Strengthening of alloys by refining grains to the nanometer scale

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Processing of metallic alloys through severe plastic deformation (SPD) promises the creation of a new class of materials that have a combination of beneficial properties, such as ultra high formability, high specific strength, high toughness and high electrical and thermal conductivity.  Key to the improved properties is the creation of a nanosized structure and stresses and strains in the material at the nanometer scale.

Project Overview

In the search for materials with improved mechanical properties severe plastic deformation (SPD) has attracted wide attention due to the strength increase that can surpass that of the strongest steels. The strength increase in metallic alloys due to SPD is caused primarily by lattice defects in the form of grain boundaries and dislocations. To fully exploit the capabilities of SPD and optimize the material's microstructure we need models that are able to predict these structures and predict the resulting mechanical properties. The work of a group of researchers led by Prof Marco Starink is dedicated to this research. The work has involved many collaborators, including international collaborations with researchers in the US, India, China, Norway and Australia.

Recent exciting progress has involved the production of a Mg-based alloy with an average grain size of 33 nm. This grain size is substantially smaller than any hitherto reported work on bulk-processed Mg-based alloys or Al-based alloys. The record grain refinement has been shown to be due to the combination of intense shearing and interaction of dislocations with nanosized rare earth containing precipitates in a heat-treated Mg-Gd-Y-Zn alloy.

Transmission electron microscopy images of a 7xxx series aluminium alloy before severe plastic deformation by high pressure torsion
Before deformation
Transmission electron microscopy images of a 7xxx series aluminium alloy after severe plastic deformation by high pressure torsion
After deformation

 

 

 

 

 

 

 

 

 

 

The picture on the left shows the triple point of 3 grains which are several micrometers in size with very limited deformation. (Deformation is evidenced by the few bands of contrast and dislocation lines.)

The picture on the right shows very small grains (about 0.1 micrometer= 100 nanometers), with evidence of high local deformation.

Associated research themes

Materials and Surface Engineering

Related research groups

Engineering Materials
Schematic diagram of HPT machine
Schematic diagram of HPT machine

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