Physical Theory of Superplastic Flow in Spatially Extended Crystalline Systems

摘要

Superplastic behavior of microsample of Zn-20.2%Al-1.8%Cu alloy at room temperature in axial tension test inside of the scanning electron microscopy has been investigated widely by the application of a new technique to study the granular flow during Superplastic deformation. The main results revealed that: (ⅰ) Cellular dislocations are the principal mechanism of Superplastic deformation, (ⅱ) Cooperative grain boundary sliding is associated with the dislocated cellular structures described by Morral and Ashby and proposed by Zelin and Mukherjee to describe some fundamental aspects of superplasticiry. (ⅲ) The mapping of the granular flow is in qualitative agreement with similar flow diagrams obtained previously by Ashby and Verrall from their oil emulsion model, (ⅳ) Linear relationship between velocity of grains in the sample and distances along tension axis obey an expression similar to the Hubble law related to the linear relationship between recessional velocity of galaxies in the cosmic structure and its distance during the expansion process of the universe, in addition to this analogous behavior the expansion rate of the universe in steady state conditions could be expressed in mathematical terms by the relationship for Superplastic flow proposed by Langdon, and (ⅴ) The hyperbolic granular flow lines during Superplastic flow are similar to the lines of force for gravitational waves. On the basis of those evidences a physical theory of Superplastic flow in spatially extended crystalline systems is proposed.