Severe plastic deformation
Severe plastic deformation (SPD) is a generic term describing a group of metalworking techniques — or more generally, solid-state mechanical processes — that involve very large strains, resulting in a high defect density and equiaxed "ultrafine" grain (UFG) size (d < 1000 nm) or nanocrystalline (NC) structure (d < 100 nm). == History == The significance of SPD was known from ancient times, at least during the transition from the Bronze Age to the Iron Age, when repeated hammering and folding were employed for processing strategic tools such as swords.
Source: Wikipedia — Severe plastic deformation (CC BY-SA 4.0)