Formability of Ultrafine Grained Metals Produced by Severe Plastic Deformation–An Overview

Abstract

Severe plastic deformation (SPD) techniques have attracted considerable attention due to their capability to refine the grain size of metals and alloys down to the ultrafine grained (UFG) regime. A characteristic feature of SPD processes is that they generate semi-finished parts such as rods or sheets, which require further shaping in order to become marketable products. One approach for the shaping of SPD processed materials is the use of metal forming processes, which can be a challenge with regard to the low work hardening rate and tendency to strain localizations of most UFG metals. This article summarizes the current state of knowledge on the formability and forming behavior of UFG metals under different loading scenarios, discussing both limitations and application potential. Furthermore, the interaction between microstructural aspects and the formability, such as the occurrence of strain localizations during and the role of heat treatments are also addressed. Given that the formability of UFG metals has received far less attention than other aspects so far, this work also aims at identifying apparent contradictions as well as scientific and technological questions that need to be addressed in future to expand the current knowledge of the field.