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»ã±¨±êÌâ(Ó¢ÎÄ)£ºStudying incipient plasticity and dislocation nucleation in crystalline solids using nanoindentation techniques

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»ã±¨ÄÚÈݼò½é£ºWe recently performed nanoindentation tests on single-crystal Mo and Ni, and a coarse-grained, high entropy FeCoCrMnNi alloy to investigate the nature of the onset of yielding. In the case of single crystals, the critical shear stress for the first pop‐in was ~1/7 of the shear modulus in both crystals. The dependence of pop‐in probability on load was understood in terms of a thermally activated dislocation nucleation process. A comparison of the activation energies suggests nucleation of full dislocations in BCC-Mo and partial dislocations in FCC‐Ni. In the case of high‐entropy FCC‐FeCoCrMnNi alloy, we found that the maximum shear stress required to initiate plasticity was within 1/15 to 1/10 of the shear modulus and relatively insensitive to grain orientation. The stress was strongly dependent upon the temperature, indicating a thermally activated process. Using a statistical model developed by Schuh et al, both the activation volume and activation energy were measured and further compared with existing dislocation nucleation models. It appeared that a mechanism consisting of a heterogeneous dislocation nucleation process with vacancy‐like defects (~3 atoms) as the rate-limiting nuclei was dominant.

»ã±¨È˼ò½é(ÖÐÎÄ)£ºT.G. Nieh½ÌÊÚÌïÄÉÎ÷´óѧ×ÊÁÏ¿ÆѧÓ빤³Ìϵ ½ÌÓý¾­Àú˹̹¸£´óѧ»ñµÃ×ÊÁÏ¿ÆѧÓ빤³Ì²©Ê¿Ñ§Î»»ªÊ¢¶Ù´óѧ»ñµÃÎïÀíѧ˶ʿ̨Íå¹úÁ¢³É¹¦´óѧ»ñµÃÎïÀíѧѧʿ ¹¤×÷¾­Àú 1980-1992£¬Âå¿ËÏ£µÂµ¼µ¯Ó뺽Ì칫˾£¨´Ë¿ÌΪÂå¿ËÏ£µÂ£­Âí¶¡¹«Ë¾£©£¬³¢ÊÔÊÒ×ÊÉî×êÑÐÔ± 1992-2004£¬ÀÍÂ×˹Àû¸¥Äª¶û¹ú¶È³¢ÊÔÊÒ£¬×ÊÉî×êÑÐÔ± 2004Äê8ÔÂ-½ñ£¬ÌïÄÉÎ÷´óѧ×ÊÁÏÓ빤³Ìϵ£¬½ÌÊÚ PUBLICATIONS Nieh½ÌÊÚÓëËûÈ˺Ï×÷£¬ÔÚ×ÊÁϺÍ×ÊÁÏÓйصÄÁìÓò°ä·¢Á˳¬¹ý400ƪµÄѧÊõÂÛÎÄ¡£Ëû׫дµÄ½Ì²Ä¡¶½ðÊôºÍÌմɵij¬ËÜÐÔ¡·ÔÚ½£ÇÅ´óѧ³ö°æÉç³ö°æ¡£ËûµÄÖØÒª×êÑÐÁìÓòΪ×ÊÁϵÄÁ¦Ñ§»úÄÜ£¬Ô̺¬Á˸ßìغϽ𡢽ðÊô²£Á§¡¢ÄÉÃ×¾§×ÊÁÏ¡¢³¬ËÜÐԺͳ¬ËܳÉÐΡ¢Çá½ðÊôÂÁºÍþºÏ½ð¡¢½ðÊô»ù¸´ºÏ»ïÁÏ¡¢½ðÊô¼ä»¯ºÏÎï¡¢³¬¸ßκϽð¡¢ÉúÎïÌÕ´É¡¢±¡Ä¤ºÍÄÉÃײãƬ×ÊÁÏ¡£ Éç»á¼æÖ°ÃÀ¹úTMSºÍASM»áÔ±×Ô2003ÄêÒÔÀ´£¬³ÉΪISI¸ßÒýÓÃ×ÊÁÏ¿Æѧ¼Ò£¬ÒýÓôÎÊý³¬¹ý10,000£¬HÖ¸Êý55 ´Ë¿Ìµ£ÈÎIntermetallicÊÇÔÓÖ¾µÄÖ÷±à 2009-2013µ£ÈÎMaterials LettersÔÓÖ¾µÄÖ÷±à¶à¸öרҵЭ»áµÄίԱ»á³ÉÔ±¿éÌå·Ç¾§ºÏ½ð¹ú¼Ê×êÑлáµÄ×éÖ¯Õß
»ã±¨È˼ò½é(Ó¢ÎÄ)£ºProfessor T.G. Nieh Department of Materials Science and Engineering, University of Tennessee EDUCATION PhD in Materials Science and Engineering, Stanford University. MS in Physics, University of Washington in Seattle. BS in Physics, National Cheng–Kung University in Taiwan. PROFESSIONAL EXPERIENCE Lockheed Missiles and Space Co. (now Lockheed-Martin), 1980-1992, as Senior Member of the lab. Lawrence Livermore National Laboratory, 1992-2004, as Senior Fellow Professor, Materials Science and Engineering, University of Tennessee, from August 2004-present. PUBLICATIONS Dr. Nieh has co–authored over 400 technical papers in a broad range of materials and material–related fields. He wrote a textbook "Superplasticity in Metals and Ceramics" published by Cambridge University Press. His main interest is the mechanical behavior of materials, include high-entropy alloys, metallic glasses, nanocrystalline materials, superplasticity and superplastic forming, lightweight aluminum and magnesium alloys, metal-matrix composites, intermetallics, ultrahigh temperature alloys, bioceramics, thin films and nanolaminates. SYNERGISTIC ACTIVITIES Society Fellow, TMS and ASM ISI Highly-cited Materials Scientist, since 2003. Citation no. over 10,000, H-index 55. Editor-in-Chief, Journal of Intermetallics, now. Editor, Materials Letters, since 2009-2013. Committee members of several professional societies Organizer of International Conferences on Bulk Metallic Glasses series