In polycrystalline metals, although the grain boundary has the important role of hindering dislocation movement and strengthening the material, when the grain size of the material is reduced to the nanoscale, the grain boundary will become unstable. The main performance is that various mechanical loadings at room temperature (unidirectional stretching, fatigue, indentation loading, etc.) can induce significant grain growth and grain boundary migration. On the other hand, due to the reduction in grain size, the motion of incomplete dislocations in face-centered cubic metals and the resulting twinning behavior become more prominent. The key scientific question is: Is the grain growth / grain boundary migration at the nanoscale related to twin formation at this scale? If so, what role does twin formation play in the process of grain growth? Recently, a research group led by Zhang Guangping, a researcher of the Materials Fatigue and Fracture Research Department of the Shenyang National Institute of Materials Science, Institute of Metal Research, Chinese Academy of Sciences (including doctoral student Luo Xuemei and associate researcher Zhu Xiaofei) passed the nano-scale face-centered cubic structure of gold thin film fatigue The atomic scale observation and theoretical analysis of grain growth under loading reveal the physical mechanism of twin-assisted nano-growth growth. This study found that fatigue loading at room temperature resulted in grain growth in a 20 nm thick gold film with an average grain size of 19 nm; meanwhile, the number of twinned grains increased significantly. Nano-scale multiple twins appear in most grown grains. Through the observation and analysis on the atomic scale, it is found that the formation of nano twins is an effective way to assist grain growth. This physical process is: the formation of twins under fatigue loading can gradually change the local orientation of the grains, and promote the decomposition of the grain boundaries into easily migrated fragments (Figure 1); as the cycle number increases, the two grains pass Mutual twin formation and continuous decomposition of the grain boundaries gradually merge and grow into one grain. To this end, the researchers proposed a new physical mechanism of "twin-assisted nano-scale gold film grain growth" under cyclic loading (Figure 2). The significance of this research result is: on the one hand, it clearly reveals the basic mechanism of twinning-assisted nanogrowth growth under fatigue loading and the existence of the difference in grain orientation under this mechanism (Figure 3), clarifying the twinning The limited growth of the auxiliary nano-grain can consume cyclic plasticity to a certain extent and slow down the formation of fatigue damage, which has a significant effect on the improvement of the fatigue strength of the metal film; on the other hand, the nano-scale metal film and the nanocrystalline metal material crystal Boundary design and utilization and regulation of grain boundary stability have important reference value for the development of structural metal materials with high strength and high fatigue reliability. Related papers have been published online in Nature-Communication on January 3, 2014 (Nature Communications 5: 3021 (2014), DOI: 10.1038 / ncomms4021). This research was supported by the National Natural Science Foundation of China, the “973†project of the Ministry of Science and Technology, and the Shenyang Materials Science National (Joint) Laboratory-oriented project. Figure 1 Observation of the microstructure of 20 nm thick gold film after cyclic loading. a, d are coarsened grains with multiple twins; b, c and e, f are enlarged views of the corresponding areas. Scale: a and df are 5 nm, b and c are 1 nm. Figure 2 Schematic diagram of the physical mechanism of twin-assisted nano-growth Fig. 3 The relationship between grain orientation differences suitable for twin-assisted nanograin growth ZENGHUI PAPER PACKAGE is a good Apparel Packaging manufacturers and
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New progress in the study of the mechanism of nano-scale metal film grain growth under fatigue loading