page_title: Severe plastic deformation
section_title: High pressure torsion
hierarchical_section_title: Severe plastic deformation / Methods / High pressure torsion
caption_attribution_description: English: Drawing of HPT
context_page_description: Severe plastic deformation is a generic term describing a group of metalworking techniques involving very large strains typically involving a complex stress state or high shear, resulting in a high defect density and equiaxed "ultrafine" grain size or nanocrystalline structure.
context_section_description: High pressure torsion (HPT) can be traced back to the experiments that won Percy Bridgman the 1946 Nobel Prize in Physics, though its use in metal processing is considerably more recent. In this method, a disk of the material to be strained is placed between 2 anvils. A large compressive stress (typically several gigapascals) is applied, while one anvil is rotated to create a torsion force. HPT can be performed unconstrained, in which the material is free to flow outward, fully constrained, or to some degree between in which outward flow is allowed, but limited.
caption: During the constrained HPT process, the material experiences shear deformation between a fixed and a rotating anvil, without losing its original dimensions.
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