Haouaoui, Mohammed (2005-12). An investigation of bulk nanocrystalline copper fabricated via severe plastic deformation and nanoparticle consolidation. Doctoral Dissertation. Thesis uri icon


  • Ultrafine grained (UFG) and nanocrystalline materials have attracted considerable
    interest because of their unique mechanical properties as compared with coarse grained
    conventional materials. The fabrication of relatively large amounts of these materials still
    remains a challenge, and a thorough understanding of the relationship between
    microstructure and mechanical properties is lacking. The objective of this study was to
    investigate the mechanical properties of UFG and nanocrystalline copper obtained
    respectively by a top down approach of severe plastic deformation of wrought copper and
    a bottom up approach of consolidation of copper nanoparticles using equal channel
    angular extrusion (ECAE). A critical assessment and correlation of the mechanical
    behavior of ECAE processed materials to the microstructure was established through the
    determination of the effect of strain level and strain path on the evolution of strength,
    ductility and yield anisotropy in UFG oxygen free high conductivity copper in correlation
    with grain size, grain morphology and texture.
    ECAE was shown to be a viable method to fabricate relatively large
    nanocrystalline consolidates with excellent mechanical properties. Tensile strengths as
    high as 790 MPa and fracture strain of 7 % were achieved for consolidated 130nm copper powder. The effects of extrusion route, number of passes and extrusion rate on
    consolidation performance were evaluated. The relatively large strain observed was
    attributed to the bimodal grain size distribution and accommodation by large grains. The
    formation of bimodal grain size distribution also explains the simultaneous increase in
    strength and ductility of ECAE processed wrought Cu with number of passes. Texture
    alone cannot explain the mechanical anisotropy in UFG wrought copper but we showed
    that grain morphology has a strong impact and competes with texture and grain
    refinement in controlling the resulting yield strength. Tension-compression asymmetry
    was observed in UFG wrought copper. This asymmetry is not always in favor of
    compression as reported in literature, and is also influenced by grain morphology through
    the interaction of dislocations with grain boundaries. Different prestrains in tension and
    compression should be experimented to have a better understanding of the encountered
    anisotropy in Bauschinger parameter in relation with the observed tension-compression

publication date

  • December 2005