Abstract
High pressure torsion (HPT) is a severe plastic deformation technique in which a small, disk-like sample is subjected to a torsional deformation under a high hydrostatic pressure. In present study, the static and dynamic tensile behaviour of commercially pure aluminium (99.6?wt%) processed by HPT is studied. The high strain rate tensile behaviour is characterized using a purpose-developed miniature split Hopkinson tensile bar setup by which strain rates up to 5 × 103?s?1 can be reached. During the tests, the deformation of a speckle pattern applied to the samples is recorded, by which local information on the strain is obtained using a digital image correlation technique. Electron back scatter diffraction images are used to investigate the microstructural evolution, more specifically the grain refinement obtained by HPT. The fracture surfaces of the tensile samples are studied by scanning electron microscopy. Results show that the imposed severe plastic deformation significantly increases the tensile strength, however, at the expense of ductility. The strain rate only has a minor influence on the materials tensile behaviour.
Highlights
Processing of metals using severe plastic deformation (SPD) is a well-established procedure for refining the grain size of bulk samples to the submicrometer or nanometer level
The grain size of the High pressure torsion (HPT) processed samples is determined by electron back scatter diffraction (EBSD)
Comparison of the two images clearly shows the obvious grain refinement obtained by the SPD process
Summary
Processing of metals using severe plastic deformation (SPD) is a well-established procedure for refining the grain size of bulk samples to the submicrometer or nanometer level. To the authors knowledge no information can be found on the high strain rate tensile behaviour of fine-grained materials. Characterisation of the mechanical behaviour of HPT processed samples is not obvious, because of the intrinsic heterogeneity and small size of the samples. Both necessitate a local measurement approach for the strain. The short test duration and the generally reduced deformation capacity of the sample, make accurate characterization of the tensile response even more difficult. Fracture surfaces of the static and dynamic tensile samples are observed using Scanning Electron Microscopy (SEM)
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