Superplasticity of metals: Phenomenology based on rheological properties and structural dynamics

Fine structure superplasticity (FSSP), high strain rate superplasticity (HSRSP) and phase transformation superplasticity (PTSP) as well as superplastic-like behaviour of some natural and industrial materials evidently belong to the same type of rheological behaviour i.e. non-linear viscoplastic now. Temperature map has been proposed as a base for rheological analysis of various types of superplastic and superplastic-like now of metallic materials. A phenomenological model has been developed to describe deformation of polycrystalline materials at elevated temperatures in a nide range of strain rates with respect to structure evolution during deformation. Rheological analysis of FSSP, HSRSP and PTSP materials along with a slurry during rheocasting shows similarities and peculiarities of superplastic and superplastic-like behaviour. The value of apparent viscosity seems to be an informative index for estimation of rheological and physical ate of grain boundaries as a viscous phase and of polycrystalline material as a whole. A new process of impulse bulk forming is presented to show unique possibility of joining in one process two stages of a regular superplastic technology i.e. preparation of ultrafine grain structure followed by HSRSP deformation.