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Grain Boundary Sliding and Amorphization are Responsible for the Reverse Hall-Petch Relation in Superhard Nanocrystalline Boron Carbide

Guo, Dezhou and Song, Shuangxi and Luo, Ruichun and Goddard, William A., III and Chen, Mingwei and Reddy, Kolan Madhav and An, Qi (2018) Grain Boundary Sliding and Amorphization are Responsible for the Reverse Hall-Petch Relation in Superhard Nanocrystalline Boron Carbide. Physical Review Letters, 121 (14). Art. No. 145504. ISSN 0031-9007. doi:10.1103/PhysRevLett.121.145504.

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The recent observation of the reverse Hall-Petch relation in nanocrystalline ceramics offers a possible pathway to achieve enhanced ductility for traditional brittle ceramics via the nanosize effect, just as nanocrystalline metals and alloys. However, the underlying deformation mechanisms of nanocrystalline ceramics have not been well established. Here we combine reactive molecular dynamics (RMD) simulations and experimental transmission electron microscopy to determine the atomic level deformation mechanisms of nanocrystalline boron carbide (B_4C). We performed large-scale (up to ∼3 700 000  atoms) REAXFF RMD simulations on finite shear deformation of three models of grain boundaries with grain sizes from 4.84 (135 050 atoms) to 14.64 nm (3 702 861 atoms). We found a reverse Hall-Petch relationship in nanocrystalline B_4C in which the deformation mechanism is dominated by the grain boundary (GB) sliding. This GB sliding leads to the amorphous band formation at predistorted icosahedral GB regions with initiation of cavitation within the amorphous bands. Our simulation results are validated by the experimental observations of an intergranular amorphous GB phase due to GBs sliding under indentation experiments. These theoretical and experimental results provide an atomistic explanation for the influence of GBs on the deformation behavior of nanocrystalline ceramics, explaining the reverse Hall-Petch relation.

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Goddard, William A., III0000-0003-0097-5716
An, Qi0000-0003-4838-6232
Additional Information:© 2018 American Physical Society.c Received 4 June 2018; published 4 October 2018. This work is supported by National Science Foundation (CMMI-1727428). Q. A. was also supported by the U.S. Nuclear Regulatory Commission (NRC-HQ-84-15-G-0028). K. M. R. is supported by National Science Foundation China (Grant No. 51850410501) and seed funding from the School of Materials Science and Engineering at Shanghai Jiao Tong University (China). S. S. is supported by MOST 973 of China (Grant No. 2015CB856800). We would like to thank Professor Qiang Guo in the ShangHai JiaoTong University for use of the Fishone 1040 Nanomill system. We also thank Professor Shinoda at the Tokyo Institute of Technology (Japan) for providing as-synthesized n-B_4C samples for experimental observations. The authors declare no competing financial interests.
Funding AgencyGrant Number
Nuclear Regulatory CommissionNRC-HQ-84-15-G-0028
National Science Foundation of China51850410501
Shanghai Jiao Tong UniversityUNSPECIFIED
Ministry of Science and Technology (Taipei)2015CB856800
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Issue or Number:14
Record Number:CaltechAUTHORS:20181008-100844030
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:90149
Deposited By: Tony Diaz
Deposited On:08 Oct 2018 17:30
Last Modified:16 Nov 2021 00:41

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