2026 Maj Local High Pressure Torsion AA5083

Local High-Pressure Torsion (L-HPT) is a recently developed technological process that induces severe plastic deformation (SPD) within a boundary layer (BL) beneath a slowly rotating punch pressed against a metallic plate. In contrast to conventional high-pressure torsion (HPT), where the severe plastic deformation zone extends through the entire thickness of the processed metallic disk, the depth of such a zone and its microstructure after L-HPT are not known in advance and have not been previously investigated. Such novel results, obtained using scanning electron microscopy and nanoindentation, are presented in this work for an AA5083 aluminum alloy as a model system. Unlike conventional dry friction conditions, where BL thickness typically does not exceed ~10 μm, electron backscatter diffraction (EBSD) measurements have revealed that the BL with an ultrafine-grained (UFG) structure that develops near the contact interface between an AA5083 aluminum alloy sample and a rotating punch can reach the thickness of up to 500 μm, starting from about 2 mm distance from the rotation center. A gradient microstructure is observed in this region, with an average grain size of about 100–200 nm in the layer immediately adjacent to the punch surface with a thickness of about 50 μm. Within this layer, a Mackenzie-type random misorientation distribution is identified, associated with extreme shear strain and saturation flow stress. This is accompanied by a slightly noticeable trend toward an increase in nanohardness in the vicinity of the contact surface.