Once the deformation twins have been activated in the copper alloys at 50% rolling reduction, will the fraction of deformation twins increase with the increase of rolling reduction? I have known the deformation twins are affected by grain size, rolling temperature, strain rate and stacking fault energy. But, how the strain level influence the fraction of deformation twins and thickness of the twin/matrix lamella? can I believe that more deformation twins are formed with the increase of true strain?
Similar to the case that increasing the strain of cold rolling increases the density of dislocations in alloys, increasing the strain of cold rolling also increases the density of deformation twins (or decreases the thicknesses of twin/matrix lamellae) if twinning is a deformation mode of the materials.
Dear LIao, thank you for your instant answer.
The critical twin nucleus thickness can be described by the equation (1) in the following reference. The driving stress of twin nucleation may be related with the flow stress. With the increase of the rolling reduction, the flow stress increases and thus induces more deformation twins and the decrease of the twin/matrix lamellae.
Article Effect of stacking-fault energy on deformation twin thicknes...
Dear Rengen Lee
It is worth take into account that with increase in the deformation, twins rotate in such a way that twinning planes are almost parallel to the rolling plane and the twinning system is stopped (M. Wróbel, M. Blicharski, S. Dymek, J. Gazdowicz, “Influence of strain path on texture and microstructural development in polycrystalline Cu and Cu-5 wt % Al alloy”, La Revue de Métallurgie-CIT/Science et Génie des Matériaux, 94 (9) (1997) 1045; M. Blicharski, S. Dymek, M. Wróbel, "Inhomogeneities of Microstructure Evolved in Metals under Plastic Deformation", Journal of Materials Processing Technology, 53 (1995) 75)
Yours Mirek
Dear M. Wrobel,
For FCC structures like Cu-Al alloys, there are four groups of {111}, i.e., (111), (-111), (1-11), and (11-1), that can act as twinning planes. Maybe one twinning system has zero resolved shear stress just because the twinning planes are parallel to the rolling plane, other twinning systems would be activated. In general, it is true that increasing strain leads to a higher twin density. We have a comprehensive review on twinning in nanocrystalline materials published in Progress in Materials Science 57 (2012) 1–62. Some of our discussion in the review is applicable in coarse-grained materials.
Regards
Xiaozhou Liao
Dear Xiaozhou Liao
of course, other twin systems are available, but the duplex twinning (i.e., twinning in the twin volume) and twinning in the matrx (separating twins) is limited due to their small thickness . In my opinion rate of growth in the twinning volume depends on the texture. The initial grain size is also very important, as you noticed.
Yours
Mirek
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