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In the process of the generation of jet formed by the shaped charge explosive compression, the grain of the metal liner is refined from 30-80 μm down to sub-micron or nanometer level. There is a strong scientific significance for studying the mechanism of grain refinement and dynamic superplastic deformation at a micro level. The main contents of this study are as follows. Firstly, the models of nanocrystalline copper with the grain sizes of 7.17, 9.11, 12.55, 14.85, 18.38 and 22.48 nm are established using the Voronoi geometrical construction method, and these models are relaxed in 100 ps to the equilibrium state at 293 K. Then, the tensile deformation processes of nanocrystalline copper at various grain sizes are simulated by using the molecular dynamics method. The strain increases to 0.2 gradually at a strain rate of 2×109/s. Based on the data output, the stress-strain curves at different grain sizes are gained and the corresponding values of the averaged flow stress are calculated. The results show that the average flow stress exhibits the maximum at a grain size of 14.85 nm. Finally, the primary deformation process of nanocrystalline copper is displayed by analyzing the atomic configuration evolvement. When the grain size is 22.48 nm, the typical dislocation motion is found and there are a huge number of dislocations in the deformation process. However, the number of dislocations decreases sharply at the grain sizes of 14.85 nm and 9.11 nm, and the grain-boundary motion is visible at these small grain sizes. The most significant work is that the deformation mechanisms of nanocrystalline copper at different grain sizes are analyzed in detail. The results indicate that the dislocation motion dominates the deformation process when the grain sizes of nanocrystalline copper are larger than 14.85 nm. As the grain sizes decrease below 14.85 nm, the grain-boundary sliding and rotation become a dominant deformation mechanism. This change of deformation mechanism is the fundamental reason for softening, which is so-called reverse Hall-Petch relationship. On the basis of previous study and this molecular dynamics simulation, combining the grain coalition and the grain-boundary rotation, an ideal deformation mechanism model is established at small grain sizes, which provides the microcosmic deformation mechanism reference for the large strain deformation of the jet.
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Keywords:
- molecular dynamics simulation /
- dynamic superplastic deformation mechanism /
- uniaxial tension /
- reverse Hall-Petch relationship
[1] Tao G, Chen H, Shen Q C 2008 Explosion and Shock Waves 28 336 (in Chinese) [陶钢, 陈昊, 沈钦灿 2008 爆炸与冲击 28 336]
[2] Tian W H 2003 Mater. Sci. Eng. A 350 160
[3] Murr L E, Trillo E A, Pappu S 2002 J. Mater. Sci. 37 3337
[4] Trillo E A 2002 Mater. Charact. 48 407
[5] Chokshi A H, Meyers M A 1990 Scr. Metall. 24 605
[6] Li J C M 1961 J. Appl. Phys. 32 525
[7] Murr L E 1997 Mater. Sci. Eng. A 222 118
[8] Meyers M A, Nesterenko V F, LaSalvia J C, Xue Q 2001 Mater. Sci. Eng. A 317 204
[9] Meyers M A, Mishra A, Benson D J 2006 JOM 58 41
[10] Daw M S, Baskes M I 1983 Phys. Rev. Lett. 50 1285
[11] Schiøtz J, Karsten W J 2003 Science 301 1357
[12] Garritt J T, Shreevant T, Jonathan A Z, David L M 2012 J. Mech. Phys. Solids 60 471
[13] Zhang H W, Fu Y F, Zheng Y G, Ye H F 2014 Phys. Lett. A 378 736
[14] Yuan L, Jing P, Liu Y H, Xu Z H, Shan D B, Guo B 2014 Acta Phys. Sin. 63 016201 (in Chinese) [袁林, 敬鹏, 刘艳华, 徐振海, 单德彬, 郭斌 2014 63 016201]
[15] He A M, Shao J L, Wang P, Qin C S 2010 Acta Phys. Sin. 59 8836 (in Chinese) [何安民, 邵建立, 王裴, 秦承森 2010 59 8836]
[16] Ma W, Lu Y W 2013 Acta Phys. Sin. 62 036201 (in Chinese) [马文, 陆彦文 2013 62 036201]
[17] Kadau K, Germann T C, Lomdahl P S, Holian B L, Kadau D, Entel P, Kreth M, Westerhoff F, Wolf D E 2004 Metall. Mater. Trans. A 35 2719
[18] Keblinski P, Wolf D, Phillpot S R, Gleiter H 1999 Scr. Mater. 41 631
[19] Chen D 1995 Comput. Mater. Sci. 3 327
[20] Hoover W G 1989 Phys. Rev. A 40 2814
[21] Mishin Y, Mehl M J, Papaconstantopoulos D A, Voter A F, Kress J D 2001 Phys. Rev. B 63 224106
[22] Li D, Wang F C, Yang Z Y, Zhao Y P 2014 Sci. China: Phys. Mech. Astron. 57 2177
[23] Honeycutt J D, Andersen H C 1987 J. Phys. Chem. 91 4950
[24] Yuan F P 2012 Sci. China: Phys. Mech. Astron. 55 1657
[25] Kumar K S, Swygenhoven H V, Suresh S 2003 Acta Mater. 51 5743
[26] Liao X Z, Srinivasan S G, Zhao Y H, Baskes M I, Zhu Y T 2004 Appl. Phys. Lett. 84 3564
[27] Wang Y M, Ma E, Chen M W 2002 Appl. Phys. Lett. 80 2395
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[1] Tao G, Chen H, Shen Q C 2008 Explosion and Shock Waves 28 336 (in Chinese) [陶钢, 陈昊, 沈钦灿 2008 爆炸与冲击 28 336]
[2] Tian W H 2003 Mater. Sci. Eng. A 350 160
[3] Murr L E, Trillo E A, Pappu S 2002 J. Mater. Sci. 37 3337
[4] Trillo E A 2002 Mater. Charact. 48 407
[5] Chokshi A H, Meyers M A 1990 Scr. Metall. 24 605
[6] Li J C M 1961 J. Appl. Phys. 32 525
[7] Murr L E 1997 Mater. Sci. Eng. A 222 118
[8] Meyers M A, Nesterenko V F, LaSalvia J C, Xue Q 2001 Mater. Sci. Eng. A 317 204
[9] Meyers M A, Mishra A, Benson D J 2006 JOM 58 41
[10] Daw M S, Baskes M I 1983 Phys. Rev. Lett. 50 1285
[11] Schiøtz J, Karsten W J 2003 Science 301 1357
[12] Garritt J T, Shreevant T, Jonathan A Z, David L M 2012 J. Mech. Phys. Solids 60 471
[13] Zhang H W, Fu Y F, Zheng Y G, Ye H F 2014 Phys. Lett. A 378 736
[14] Yuan L, Jing P, Liu Y H, Xu Z H, Shan D B, Guo B 2014 Acta Phys. Sin. 63 016201 (in Chinese) [袁林, 敬鹏, 刘艳华, 徐振海, 单德彬, 郭斌 2014 63 016201]
[15] He A M, Shao J L, Wang P, Qin C S 2010 Acta Phys. Sin. 59 8836 (in Chinese) [何安民, 邵建立, 王裴, 秦承森 2010 59 8836]
[16] Ma W, Lu Y W 2013 Acta Phys. Sin. 62 036201 (in Chinese) [马文, 陆彦文 2013 62 036201]
[17] Kadau K, Germann T C, Lomdahl P S, Holian B L, Kadau D, Entel P, Kreth M, Westerhoff F, Wolf D E 2004 Metall. Mater. Trans. A 35 2719
[18] Keblinski P, Wolf D, Phillpot S R, Gleiter H 1999 Scr. Mater. 41 631
[19] Chen D 1995 Comput. Mater. Sci. 3 327
[20] Hoover W G 1989 Phys. Rev. A 40 2814
[21] Mishin Y, Mehl M J, Papaconstantopoulos D A, Voter A F, Kress J D 2001 Phys. Rev. B 63 224106
[22] Li D, Wang F C, Yang Z Y, Zhao Y P 2014 Sci. China: Phys. Mech. Astron. 57 2177
[23] Honeycutt J D, Andersen H C 1987 J. Phys. Chem. 91 4950
[24] Yuan F P 2012 Sci. China: Phys. Mech. Astron. 55 1657
[25] Kumar K S, Swygenhoven H V, Suresh S 2003 Acta Mater. 51 5743
[26] Liao X Z, Srinivasan S G, Zhao Y H, Baskes M I, Zhu Y T 2004 Appl. Phys. Lett. 84 3564
[27] Wang Y M, Ma E, Chen M W 2002 Appl. Phys. Lett. 80 2395
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