A series of high - resolution images of twin growth and deuteronization at the crack tip of pure aluminum in in situ drawing process . The twinning boundary contour is represented by a dotted line, and L1-L7 is a Shockley dislocation step on the twin boundary. The left side of TD (ac) is the twin growth process where L1-L4 dislocation steps move forward. The right picture (ad) shows the process of the untwisting process in which the L5-L7 dislocation step moves back to the crack tip until the twin completely disappears.
The National Institute of Materials Science, Shenyang Institute of Metal Research, Chinese Academy of Sciences has made important progress in the research of the reversible twinning mechanism of pure aluminum. Li Baiqing, a doctoral student in Solid Atomic Imaging Research Department, under the guidance of his mentor, Professor Ren Manling and Prof. Mao Xingyuan of the University of Pittsburgh, used in-situ tensile high-resolution electron microscopy to observe that coarse-grained pure aluminum can not only deform under high stress. Crystal, and its deformation twins are reversible, accompanied by a spontaneous deuteration process. With the help of the research group of Marx and Professor Johns Hopkins University in the United States, molecular dynamics simulations further confirmed the spontaneous deuteronization process in pure aluminum. Studies have shown that the cause of spontaneous devitrification can be attributed to the high stacking fault energy of pure aluminum and the lower resistance to Shockless's incomplete dislocation movement. This kind of spontaneous reversible deformation twins may become a new mechanism that is commonly found in the deformation of high-level dissimilar metals. The study was published online on May 20th by the Physical Review Letters.
For many metals, the twinning process is usually irreversible, so deformation twins become an important plastic deformation mechanism. However, for pure aluminum with high-level error energy, the traditional view is that no deformation twins will occur. In 2003, Chen et al. reported on Science that deformed twins were produced in nanocrystalline aluminum. They believe that the generation of deformation twins is directly related to the size of the nanocrystals. As the grain size is reduced to several tens of nanometers, the deformation mechanism is shifted to the mechanism dominated by partial dislocations due to the full dislocation slip mechanism, so that deformation twinning and stacking faults can be observed in the nanocrystalline aluminum. So, in normal pure aluminum, can it really not produce deformation twins? Or can it be deformed twins but rarely observed? Due to the lack of convincing experimental evidence, it has been impossible to answer these basic questions.
The author of this paper used the experimental method of in-situ stretching under a high-resolution transmission electron microscope to study the deformation behavior of ordinary pure aluminum at room temperature under the high stress state of the crack tip. The entire dynamic process of the formation and recovery of deformed twins in pure aluminum was observed in situ on the atomic scale. It was observed in real time that, under loading conditions, the growth of deformation twins is achieved by the Skokee dislocation step on twin boundaries (ie, the twin boundary migration); during the stress relaxation process, the twins stop growing. Then, the phenomenon of deuteration occurs spontaneously until the deformation twin disappears completely. In situ high-resolution TEM observations and molecular dynamics simulations all indicate that the twinning process consists of two stages. The first is that the Shockley dislocations at the twinning stage steps, under the effect of surface mirror forces, overcome the backward movement of the dislocation movement resistance, and the twinning boundary migrates to make the niobium wafer layer thinner; then, in the image force and elimination. Under the combined action of the high-energy twin-crystal interface driving force, the entire germanium wafer layer quickly disappears completely. Because the stacking error energy of aluminum is very high, the nucleation size of the deformed twins is relatively small, and not only the effect of the surface mirror force is significant, but also it is not easy to be pinned by grain boundaries and dislocations in the coarse-grained materials, so that the deformation twins can be easily realized. The full reply. Therefore, unlike the spontaneous untwisting process in which grain boundaries in nanocrystalline aluminum obstruct deformation twinning, it is difficult to observe such deformed twins in deformed ordinary pure aluminum.
The discovery of this spontaneous untwisting phenomenon in pure aluminum has enriched people's understanding of the mechanism of high-level misfit metal deformation.
This work has been funded by the "Hundred Talents Program" of the Chinese Academy of Sciences, the National Natural Science Foundation, and the National "973 Project." (According to Institute of Metal Research, Chinese Academy of Sciences
The National Institute of Materials Science, Shenyang Institute of Metal Research, Chinese Academy of Sciences has made important progress in the research of the reversible twinning mechanism of pure aluminum. Li Baiqing, a doctoral student in Solid Atomic Imaging Research Department, under the guidance of his mentor, Professor Ren Manling and Prof. Mao Xingyuan of the University of Pittsburgh, used in-situ tensile high-resolution electron microscopy to observe that coarse-grained pure aluminum can not only deform under high stress. Crystal, and its deformation twins are reversible, accompanied by a spontaneous deuteration process. With the help of the research group of Marx and Professor Johns Hopkins University in the United States, molecular dynamics simulations further confirmed the spontaneous deuteronization process in pure aluminum. Studies have shown that the cause of spontaneous devitrification can be attributed to the high stacking fault energy of pure aluminum and the lower resistance to Shockless's incomplete dislocation movement. This kind of spontaneous reversible deformation twins may become a new mechanism that is commonly found in the deformation of high-level dissimilar metals. The study was published online on May 20th by the Physical Review Letters.
For many metals, the twinning process is usually irreversible, so deformation twins become an important plastic deformation mechanism. However, for pure aluminum with high-level error energy, the traditional view is that no deformation twins will occur. In 2003, Chen et al. reported on Science that deformed twins were produced in nanocrystalline aluminum. They believe that the generation of deformation twins is directly related to the size of the nanocrystals. As the grain size is reduced to several tens of nanometers, the deformation mechanism is shifted to the mechanism dominated by partial dislocations due to the full dislocation slip mechanism, so that deformation twinning and stacking faults can be observed in the nanocrystalline aluminum. So, in normal pure aluminum, can it really not produce deformation twins? Or can it be deformed twins but rarely observed? Due to the lack of convincing experimental evidence, it has been impossible to answer these basic questions.
The author of this paper used the experimental method of in-situ stretching under a high-resolution transmission electron microscope to study the deformation behavior of ordinary pure aluminum at room temperature under the high stress state of the crack tip. The entire dynamic process of the formation and recovery of deformed twins in pure aluminum was observed in situ on the atomic scale. It was observed in real time that, under loading conditions, the growth of deformation twins is achieved by the Skokee dislocation step on twin boundaries (ie, the twin boundary migration); during the stress relaxation process, the twins stop growing. Then, the phenomenon of deuteration occurs spontaneously until the deformation twin disappears completely. In situ high-resolution TEM observations and molecular dynamics simulations all indicate that the twinning process consists of two stages. The first is that the Shockley dislocations at the twinning stage steps, under the effect of surface mirror forces, overcome the backward movement of the dislocation movement resistance, and the twinning boundary migrates to make the niobium wafer layer thinner; then, in the image force and elimination. Under the combined action of the high-energy twin-crystal interface driving force, the entire germanium wafer layer quickly disappears completely. Because the stacking error energy of aluminum is very high, the nucleation size of the deformed twins is relatively small, and not only the effect of the surface mirror force is significant, but also it is not easy to be pinned by grain boundaries and dislocations in the coarse-grained materials, so that the deformation twins can be easily realized. The full reply. Therefore, unlike the spontaneous untwisting process in which grain boundaries in nanocrystalline aluminum obstruct deformation twinning, it is difficult to observe such deformed twins in deformed ordinary pure aluminum.
The discovery of this spontaneous untwisting phenomenon in pure aluminum has enriched people's understanding of the mechanism of high-level misfit metal deformation.
This work has been funded by the "Hundred Talents Program" of the Chinese Academy of Sciences, the National Natural Science Foundation, and the National "973 Project." (According to Institute of Metal Research, Chinese Academy of Sciences