Abstract
It is well known that when coarse-grained metals undergo severe plastic deformation to be transformed into nano-grained metals, their ductility is reduced. However, there are no ductile fracture criteria developed based on grain refinement. In this paper, we propose a new relationship between ductile fracture and grain refinement during deformation, considering factors besides void nucleation and growth. Ultrafine-grained Al-Mg alloy sheets were fabricated using different rolling techniques at room and cryogenic temperatures. It is proposed for the first time that features of the microstructure near the fracture surface can be used to explain the ductile fracture post necking directly. We found that as grains are refined to a nano size which approaches the theoretical minimum achievable value, the material becomes brittle at the shear band zone. This may explain the tendency for ductile fracture in metals under plastic deformation.
Highlights
It is well known that when coarse-grained metals undergo severe plastic deformation to be transformed into nano-grained metals, their ductility is reduced
We found that as grains are refined to a nano size which approaches the theoretical minimum achievable value, the material becomes brittle at the shear band zone
Ultrafine-grained Al-Mg alloy sheets were fabricated by cold rolling, asymmetric rolling (AR), cryorolling, and Asymmetric cryorolling (ACR) respectively
Summary
It is well known that when coarse-grained metals undergo severe plastic deformation to be transformed into nano-grained metals, their ductility is reduced. Ultrafine-grained Al-Mg alloy sheets were fabricated using different rolling techniques at room and cryogenic temperatures It is proposed for the first time that features of the microstructure near the fracture surface can be used to explain the ductile fracture post necking directly. We found that as grains are refined to a nano size which approaches the theoretical minimum achievable value, the material becomes brittle at the shear band zone This may explain the tendency for ductile fracture in metals under plastic deformation. Nano-grained/ultrafine-grained bulk metals produced using severe plastic deformation (SPD) techniques show excellent mechanical properties[7,8,9,10]. All the above models assume that the fracture evolution directly depends on the www.nature.com/scientificreports strength, strain hardening capability and strain rate sensitivity of the matrix surrounding the voids None of these criteria consider the change in microstructure during ductile fracture. We found that the mean grain size near the fracture surface is much smaller than that in the matrix, and is close to the theoretical achievable minimum
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