Papers by Author: M.L. Sui

Abstract: It is generally accepted that grain refinement by the mechanisms of dislocation interaction, deformation twinning and/or stress-induced martensitic transformation is of relatively low efficiency. Rapid production of nanostructured metallic materials by conventional processing technologies remains a challenge. A new mechanism of fast grain refinement, through highly localized plastic deformation, was recently found in a -type biomedical titanium alloy (Ti2448). This mechanism leads to rapid grain refinement to tens nanometers and even amorphous transition during conventional cold processing. Since such grain refinement induces little strengthening, this process was previously termed soft nanostructuring. Here we review the research into this new way of nanostructuring and discuss the mechanism of grain refinement as well as dispersion strengthening of Ti2448 alloy by the precipitation of a second phase from the nano-sized  matrix.

Abstract: This paper reviews our recent studies on the effect of twin boundary (TB) on the deformation behavior in Cu with nanoscale growth twins. In situ straining transmission electron microscopy investigations on TB migration, TBs and twin ends acting as dislocation emission sources, and the interactions between dislocations and TBs are highlighted. Results provide some useful understanding of why Cu with nanoscale twins leads to a combination of ultrahigh strength and high ductility.

Abstract: Copper sheet samples composed of nanometer scale lamellar twins was produced by electrodeposition. The coherent lamellar twin boundaries were within 20˚ of being parallel to the sheet plane in more than 60% of the grains. The electrodeposited sample was cold rolled to 30 and 85% reductions in thickness and the structural evolution during cold rolling was examined by transmission electron microscopy (TEM) and high resolution TEM (HRTEM). Extensive activity of partial dislocations along twin boundaries and of perfect dislocations within twins (in particular in coarse twins >100nm) were identified. Moreover, it was found that shear banding occurred, which locally destroyed the lamellar twin structure. A dislocation structure developed within the shear bands, and such a structure evolved with strain and gradually replaced the lamellar twin structure. After 85% deformation, a large volume fraction of the lamellar twin structure was replaced by a lamellar dislocation structure characteristic of high strain rolling where the lamellar dislocation boundaries are almost parallel to the rolling plane. It was also found that the structural scales are coarser in the lamellar dislocation structure than in the initial lamellar twin structure.