Title

Twin nucleation, twin propagation, twin-slip interactions, pseudo-elasticity, strain-rate sensitivity and non-Schmid's effects of {10¯1 2} twinning in magnesium via in-situ EBSD

Author

Janit Kapil

Advisor

Kadiri, E. Haitham

Committee Member

Horstemeyer, Mark

Committee Member

Hammi, Youssef

Date of Degree

5-1-2011

Document Type

Graduate Thesis - Open Access

Degree Name

Master of Science

College

James Worth Bagley College of Engineering

Department

Department of Mechanical Engineering

Abstract

In-situ EBSD on profuse {10ˉ12} twinning in magnesium revealed that the twinning stress for nucleation is not totally rate-insensitive but highly dependent on grain boundary misorientation ranging between 10° and 15°. A new regime in the theta-strain curve; Regime-D, before Regime II, was identified for axisymmetric textures and corresponded to mitigation of twin propagation which was markedly rate-sensitive, such when the strain-rate fell below 10-5/s, twin propagation, but not twin nucleation, was completely halted and this fact substantiates the predominant effect of transmutation on Regime II hardening over that of Hall and Petch by twin segmentation. This technique revealed that twin nucleation dominates twin growth rate over twin propagation in grains undergoing multi-variant twinning under high-Schmid factors. Pseudo-elasticity in Mg was revealed to originate from an unusual detwinning phenomenon of residual twins. This effect was attributed to incomplete accommodation slip necessary for the shape change by twin to take place.

URI

https://hdl.handle.net/11668/16293

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