Structural metals and alloys have a vast range of applications including building, construction, bridges and other structural components. With the rapid technological advancement that has resulted to more complex structures that require various applications, a question has been raised concerning the currently available process for selection and designing the structural metals and their alloys. Although there are different designing processes, the strength-ductility trade-off emerges at the top as the current procedures used in various fields for selection and design of structures. It is however unreliable and therefore has limited the possibility of exploring and achieving more application of structural alloy especially in the emerging fields.
The need to develop steels with the desired properties for better performance has led to the development of twin-induced plasticity (TWIP), a new selection and designing process for structural metals and alloys. Although it contradicts the widely known strength-ductility trade-off, its use has been appreciated as it leads to more strong steels with higher performance capabilities. This is attributed to the interaction experienced between the various dislocations and the deformation twins. To understand this new design strategy for structural metals and alloys, a better understanding is required in predicting the various transitions witnessed in twin-induced plasticity. This is very significant in helping the designers to achieve the desired properties for different applications.
Recently, Professor Sun Ig Hong at Chungnam National University, Department of Nanomaterials Engineering in the Republic of Korea developed a deformation-mode transition model for predicting the transitions in twin-induced plasticity in solid solution copper alloys. In the study, he further predicted wavy to planar transition. This was in a bid to apply this prediction strategy in the selection and designing of high-performance materials for structural, engineering and other applications. This work is currently published in the journal, Materials Science and Engineering A.
Professor Hong observed the predicted increase in the solute content that was required for the two transition processes, that is, the first transition of wavy-slip to planar-slip and finally from planar-slip to TWIP. The accuracy of the model was further confirmed by the similarities in the predicted solute content value and that of the available experimental values in literature.
The model worked on an elementary concept that enabled the prediction of the transitions from wavy-slip to planar-slip to TWIP. It is natural that segregated solute atoms will prevent various dislocation partials separated by a stacking fault between them to come together. The formation of deformation-twinning and slip planarity increases the stress and strain hardening rate by blocking the passage of mobile dislocations in the solid solution alloys.
The high predictability of the deformation-mode transition model according to the author was due to the enhanced understanding of dislocation mechanism in twin-induced plasticity in copper alloys. This is because of the frictional-stress exerted by solute atoms that is experienced on the twinning dislocation as well as stacking fault energy. For the enhanced effects of nanotwins, their stability according to Hong needs be improved by preventing detwinning from taking place by the segregated solute atoms at the partial dislocations during twinning. This model is versatile and hence can be used for TWIP prediction even in more complex and complicated multi-components alloys. The model provides the strategy for engineering design of more advanced steels and non-ferrous alloys, with enhanced formability and mechanical strength associated with deformation-twins.
Hong, S. (2018). Criteria for predicting twin-induced plasticity in solid solution copper alloys. Materials Science and Engineering: A, 711, 492-497.
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