Superplastic Flow of Metals Extruded by KoBo Method
The extrusion of metals by the KoBo method, which is a new technological solution, allows to perform the process at low temperature with severe plastic deformation (SPD) under cyclic change of deformation path conditions. Apart from the localized plastic flow in shear bands intensive generation of point defects (self interstitials) takes place. It is important that excessive concentration of interstitial atoms is preserved in extruded products and often takes the shape of nanoclusters. Their presence causes that the effect of superplasticity (e.g. about 800% elongation of aluminum alloy 7075) does not require nanometric sizes of the grains and appears in metals extruded by the KoBo method with grains of over dozen or even several dozen micrometers. The results suggest the necessity to verify the mechanisms currently considered as decisive of the superplastic flow of metals.
Jing Tao Wang, Roberto B. Figueiredo and Terence G. Langdon
W. Bochniak et al., "Superplastic Flow of Metals Extruded by KoBo Method", Materials Science Forum, Vols. 667-669, pp. 1039-1044, 2011