Twinning in hexagonal materials: application to zirconium and magnesium

Twinning;Magnesium;Zirconium;H.c.p.;Micromechanics;EBSD

Juan, Pierre-Alexandr ; Capolungo, Laurent Mechanical Engineering Kalidindi, Surya Pierron, Olivier Garmestani, Hamid Berbenni, Stéphane ; Capolungo, Laurent

University:Georgia Institute of Technology

Department:Mechanical Engineering

关键词: Twinning;    Magnesium;    Zirconium;    H.c.p.;    Micromechanics;    EBSD;   

Others  :  https://smartech.gatech.edu/bitstream/1853/53945/1/JUAN-DISSERTATION-2015.pdf

美国|英语

来源: SMARTech Repository

【 摘 要 】

The main objective of this thesis is to investigate and quantify the influence of parent-twin and twin-twin interactions on the mechanical response of hexagonal close-packed metals. To study parent-twin interactions, a mean-field continuum mechanics approach has been developed based on a new twinning topology in which twins are embedded in twinned grains. A first model generalizing the Tanaka-Mori scheme to heterogeneous elastic media is applied to first and second generation twinning in magnesium. In the case of first generation twinning, the model is capable of reproducing the trends in the development of backstresses within the twin domain as observed experimentally. Applying the methodology to the case of second-generation twinning allows the identification, in exact agreement with experimental observations, of the most likely second-generation twin variants to grow in a primary twin domain. Because the elastic behavior assumption causes internal stress level magnitudes to be excessively high, the first model is extended to the case of elasto-plasticity. Using a self-consistent approximation, the model, referred to as the double inclusion elasto-plastic self-consistent (DI-EPSC) scheme, is applied to Mg alloy polycrystals. The comparison of results obtained from the DI-EPSC and EPSC schemes reveals that deformation system activities and plastic strain distributions within twins drastically depend on the interaction with parent domains. The influence of twin-twin interactions on nucleation and growth of twins is being statistically studied from zirconium and magnesium electron back-scattered diffraction scans. A new twin recognition software relying on graph theory analysis has been developed to extract all microstructural and crystallographical data. It is capable of identifying all twinning modes and all twin-twin interaction types occurring in hexagonal close-packed materials. The first results obtained from high purity Zr electron back-scattered diffraction maps reveal that twin-twin interactions hinder subsequent twin nucleation. They also show that mechanisms involved in twin growth may differ significantly for each twinning mode.A second study performed on AZ31 Mg presents statistics about low Schmid factor {10-12} tensile twins and about {10-12}-{10-12} sequential double twins coupled with a simplified version of the Tanaka-Mori scheme generalized to heterogeneous elasticity with plastic incompatibilities.