Journal
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
Volume 645, Issue -, Pages 298-305Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.msea.2015.08.027
Keywords
Magnesium; Twinning; Schmid factor; Geometrically necessary twins
Categories
Funding
- Center for Advanced Vehicular Systems, Mississippi State University
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Evidence for the formation of geometrically necessary twins (GNTs), or twins that accommodate a strain gradient in a multi-axial stress state, in quasi-static, room temperature three-point bending of a rolled magnesium alloy is presented. Electron backscatter diffraction analysis showed that {10 (1) over bar2} <10<(1)over bar>(1) over bar> extension twins (rather than {10 (1) over bar1} <10<(1)over bar>(2) over bar> contraction twins) form in arcs in the tension zone, and that twinned grains have very low Schmid factors. The main tensile stress component in the tension zone was nearly perpendicular to the c-axis of the parent grains. The mechanism for such unusual twinning behavior was analyzed from the perspective of strain components that are generated by {10 (1) over bar2} <10<(1)over bar>(1) over bar> twinning. After twinning, an extension strain component along the c-axis and a contraction strain component perpendicular to the c-axis of the parent lattice are generated simultaneously due to the misfit between the parent and the twin lattice. The contraction strain component by twinning provided an extra strain accommodation for the compressive strain in the tension zone produced by the bending, despite the fact that the local stress state strongly disfavored the {10 (1) over bar2} <10<(1)over bar>(1) over bar> twinning. Thus, the {10 (1) over bar2} < 10<(1)over bar>(1) over bar> twins in the arcs in the tension zone of the bent specimen present the characteristic of being geometrically necessary, similar to geometrically necessary dislocations and boundaries. (C) 2015 Elsevier B.V. All rights reserved.
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