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Báo cáo hóa học: " High P–T Nano-Mechanics of Polycrystalline Nickel Yusheng Zhao Æ T. D. Shen Æ Jianzhong Zhang"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: High P–T Nano-Mechanics of Polycrystalline Nickel Yusheng Zhao Æ T. D. Shen Æ Jianzhong Zhang | Nanoscale Res Lett 2007 2 476-491 DOI 10.1007 s11671-007-9095-z NANO REVIEW High P-T Nano-Mechanics of Polycrystalline Nickel Yusheng Zhao T. D. Shen Jianzhong Zhang Received 2 August 2007 Accepted 4 September 2007 Published online 26 September 2007 to the authors 2007 Abstract We have conducted high P-T synchrotron X-ray and time-of-flight neutron diffraction experiments as well as indentation measurements to study equation of state constitutive properties and hardness of nanocrystalline and bulk nickel. Our lattice volume-pressure data present a clear evidence of elastic softening in nanocrystalline Ni as compared with the bulk nickel. We show that the enhanced overall compressibility of nanocrystalline Ni is a consequence of the higher compressibility of the surface shell of Ni nanocrystals which supports the results of molecular dynamics simulation and a generalized model of a nanocrystal with expanded surface layer. The analytical methods we developed based on the peak-profile of diffraction data allow us to identify micro local yield due to high stress concentration at the grain-to-grain contacts and macro bulk yield due to deviatoric stress over the entire sample. The graphic approach of our strain stress analyses can also reveal the corresponding yield strength grain crushing growth work hardening softening and thermal relaxation under high P-T conditions as well as the intrinsic residual surface strains in the polycrystalline bulks. From micro-indentation measurements we found that a low-temperature annealing T 0.4 Tm hardens nanocrystalline Ni leading to an inverse Hall-Petch relationship. We explain this abnormal Hall-Petch effect in terms of impurity segregation to the grain boundaries of the nanocrystalline Ni. Y. Zhao El J. Zhang LANSCE-LC Los Alamos National Laboratory Los Alamos NM 87545 USA e-mail yzhao@lanl.gov T. D. Shen MST-8 Los Alamos National Laboratory Los Alamos NM 87545 USA Keywords Nano-mechanics Polycrystalline nickel High pressure and .