Statistical analyses of deformation twinning in magnesium

Abstract

To extract quantitative and meaningful relationships between material microstructure and deformation twinning in magnesium, we conduct a statistical analysis on large data sets generated by electron backscattering diffraction (EBSD). The analyses show that not all grains of similar orientation and grain size form twins, and twinning does not occur exclusively in grains with high twin Schmid factors or in the relatively large grains of the sample. The number of twins per twinned grain increases with grain area, but twin thickness and the fraction of grains with at least one visible twin are independent of grain area. On the other hand, an analysis of twin pairs joined at a boundary indicates that grain boundary misorientation angle strongly influences twin nucleation and growth. These results question the use of deterministic rules for twin nucleation and Hall–Petch laws for size effects on twinning. Instead, they encourage an examination of the defect structures of grain boundaries and their role in twin nucleation and growth.

Keywords:

• statistics
• hcp
• grain size
• twinning
• magnesium alloys
• polycrystalline metals

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Corrigendum

Acknowledgements

This work was performed with support from Office of Basic Energy Sciences, Project FWP 06SCPE401, under US DOE Contract No. W-7405-ENG-36.

Notes

Notes

1. The total population of grain boundaries used for determining ‘crossed’ grain boundaries statistics was larger than the population used for the other grain boundary statistics.

2. The twins with small or negative Schmid factors were most likely introduced while polishing the metallographic sections. These twins account for a very small fraction of the total number of observed twins.

3. The 8% is based on the total population of grain boundaries used for determining crossed grain boundaries statistics, which was larger than N _gb the population used for the other grain boundary statistics.

4. In sequential twinning, it is not possible to distinguish the primary from the secondary twin if both twins have traversed their parent grains.