Local High Pressure Torsion: a process for creating targeted heterogeneities in metallic materials

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In the light of recent developments in the design of structural materials, micro-architected heterogenous-structure metals are considered among most structurally efficient. In this work, a new technique for Local High Pressure Torsion (L-HPT) enabling the creation of heterogeneous structures through localised deformation processing in sheet metals by impeding a rotating punch is proposed. Using AA5083 aluminium alloy as an example, we show experimentally that the rotation of the punch sets adjacent material layers in motion. This results in more than two-fold increase in material hardness over initial level in the workpiece bulk with rather sharp gradients in hardness level transition. The maximum hardness is observed at the peripheral edge of a punch tip. Finite-element modelling of the L-HPT process confirmed that the rotational flow of workpiece material leads to the accumulation of shear strain. The level of accumulated strain increases with an increase in friction at the contact surface. Further analysis based on dimensionality theory revealed that for such an L-HPT configuration the level of equivalent strain is directly proportional to the ratio of rotation-to-translation speeds at the punch.