ON MICRO-SUPERPLASTICITY

Micro-superplasticity phenomenon, i.e. formation of thin fibers, whose appearance suggests extremely high strain in the local regions, has b een documented in a number of plastically and superplastically deforme d materials, predominantly in aluminum alloys. The fiber formation occ urs both at the fracture surface and at the deformed surface. The fibe r length increases with the total strain, and it is maximum under the optimum superplastic strain rate. An ultra-fine grain structure, a hig h concentration of oxygen and often high concentration of the alloy el ements have been observed in the fibers. Suggested explanations for fi ber formation have been reviewed, the important role of oxidation reac tions has been emphasized. (C) 1997 Acta Metallurgica Inc.