Abstract

This paper comprises an investigation using finite element analysis to study the behaviour of nanocrystalline grain structures during Equal Channel Angular Press (ECAP) processing of metals. The effects of average grain size and misorientation angle on the deformation are examined in order to see how microstructural features might explain the observed increase in strength of nanocrsytalline metals. While this approach forms a convenient starting as it offers a simple way of including grain size effects and grain misorientation to which we could add additional phenomena through developing the material model used to describe the anisotropy and techniques that would automatically re-mesh the refined grain structure produced under severe plastic deformation. From this, it can be concluded that these additional techniques incorporated into the finite element model produced effects that correspond to observed behaviour in real polycrystals.

Highlights

  • The study of nanocrystalline (NC) metals and alloys has been a topic of research since the 1950ís

  • While this approach forms a convenient starting as it offers a simple way of including grain size effects and grain misorientation to which we could add additional phenomena through developing the material model used to describe the anisotropy and techniques that would automatically re-mesh the refined grain structure produced under severe plastic deformation

  • It is easier to relate the model to real materials as it is possible to measure both grain size and the average misorientation angles physically and incorporate them into the model without having to use sophisticated methods to find model parameters

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Summary

INTRODUCTION

The study of nanocrystalline (NC) metals and alloys has been a topic of research since the 1950ís. Processing by ECAP leads to significant strengthening of the material at ambient temperatures (Valiev et al, 2002) and the structures obtained have specific features : low density of free dislocations, high angle misorientation of these grains, and high energy and non equilibrium state of grain boundaries (Morita et al, 2004). These structures lead to changes in physical and mechanical properties, a significant increase in the strength with good ductility (Meyers et al, .2006). Both the effect of grain size and high angle misorientation are important phenomena needed to describe the ECAP process

FINITE ELEMENT MODELLING OF ECAP PROCESS
FINITE ELEMENT MODELLING OF GRAIN STRUCTURE

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