Mesoscopic grain boundary sliding as the rate controlling process for high strain rate superplastic deformation

Padmanabhan, K A and Basariya, M R (2009) Mesoscopic grain boundary sliding as the rate controlling process for high strain rate superplastic deformation. Materials Science and Engineering A, 527 (1-2). pp. 225-234.

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Important features observed during high strain rate superplastic deformation are enumerated. Starting from the premise that the phenomenon of structural superplasticity in different classes of materials results when grain boundary sliding that develops to a mesoscopic scale (defined to be of the order of a grain diameter or more) controls the rate of flow, the particular case of high strain rate superplasticity is explained. The rate equation developed is validated using experimental results concerning 5 alloy systems in which an ultra-fine grain size is developed by thermomechanical processing and retained in a similar condition during superplastic deformation by fine, grain boundary pinning particles and 3 alloy composites in which the volume fraction of the reinforcing constituent is significant (15-25%). It is demonstrated that the analysis results in estimates for the externally measured strain rates that are within a factor of two, in addition to providing a physically meaningful free energy of activation for the rate controlling process. This approach explains superplastic flow in different classes of materials in terms of a single rate controlling mechanism of deformation, viz., mesoscopic grain boundary sliding, with the help of a few constants that have the same values for all systems. The system-dependent variables of threshold stress needed for the onset of mesoscopic boundary sliding and free energy of activation are obtained directly from superplasticity stress-strain rate data, without external inputs. (C) 2009 Published by Elsevier B.V.

Item Type:Article
Official URL/DOI:DOI: 10.1016/j.msea.2009.07.059
Uncontrolled Keywords:High strain rate superplasticity; Grain boundary pinning; Grain boundary sliding; Composites; Ultrafine grain size; Severe plastic deformation
Divisions:NML Chennai
ID Code:3259
Deposited By:Dr. A K Sahu
Deposited On:11 Jul 2011 17:32
Last Modified:06 Feb 2012 17:22
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