Formation of bimodal grain structures in high purity Al by reversal high pressure torsion

Bimodal grain structure was fabricated in a 99.99% purity aluminium by high pressure torsion at ambient temperature in reversal deformation mode at a strain amplitude Δε = 1, strain rate ε˙=1.1×10-1s-1 and hydrostatic pressure P = 5 GPa. Enhanced boundary mobility due to the high purity of the aluminium and homologous temperature coupled with reversal simple shear deformation are found to be responsible for bimodal microstructure formation.