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Tham khảo tài liệu 'high temperature strain of metals and alloys part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 3.8 Summary 41 type for the cubic body-centered crystal lattice. The fifth distinctive structural feature is the presence of jogs in mobile dislocations. Moreover the distances between jogs are very close to the distances between immobile dislocations in small-angle sub-boundaries. The following conclusion can be drawn the mobile dislocations arise from the sub-boundary dislocations. It is as if the former bear a stamp an imprint of the latter. The generation of vacancies during the process under consideration is the last feature. Loops and helicoids are formed when vacancies collapse. It is logical conclude that sources of vacancies are activated during the high-temperature deformation process. It should be noted that some features described above especially the formation of small-angle boundaries were observed in many studies. However we should to take into account all the structural peculiarities for an adequate understanding of the phenomenon under consideration. Now we can proceed to describe the physical mechanism ofhigh-temperature deformation of pure metals and single-phase alloys. Our aim is to relate the microstructural observations to the measured strain rates. 3.8 Summary Typical structural features are observed in pure metals and solid solutions which are loaded at high temperatures. These features are caused by certain physical mechanisms of deformation. The average subgrain sizes D and the average subgrain misorientations n have been systematically directly measured during high-temperature strain of the metals and alloys under investigation. The values of D are of the order of 0.7-2.0 pm the values of n are of the order of 2.9-6.0 mrad. The substructure is formed inside crystallites during the primary stage of creep. The value of D decreases and n increases during the primary stage. The origin of the steady-state stage coincides with the end of substructure formation. The steady-state creep occurs at almost constant mean values of both parameters. It
