Local severe plastic deformation by modified impact extrusion process

Grain refinement by the application of very high strains with changing strain path is an outstanding approach for tailoring material properties. Methods of severe plastic deformation (SPD) can create ultrafine-grained or nanostructured metallic materi-als with new combinations of physical and mechanical properties. Classical SPD methods typically focus on the uniform modification of the microstructure throughout the complete volume. The characteristics of ultrafine-grained and nanocristalline materials frequently are not required in the complete component volume. Most material failures such as fatigue fracture, corrosion or wear occur at or near the surface. Technologies of Surface Mechanical Attrition Treatment (SMAT) are available to create ultrafine-grained or nanostructured surface areas. The thickness of the ultrafine-grained area created by these processes is limited to a very thin surface layer. Thicker layers and graded material properties can be produced by incremental forming methods like gradation rolling. Grading by extrusion is of interest with respect to technical aspects and economic feasibility. The present article focuses on a new approach for partial SPD by impact extrusion.