Document Detail

Ultrahard nanotwinned cubic boron nitride.
MedLine Citation:
PMID:  23325219     Owner:  NLM     Status:  PubMed-not-MEDLINE    
Cubic boron nitride (cBN) is a well known superhard material that has a wide range of industrial applications. Nanostructuring of cBN is an effective way to improve its hardness by virtue of the Hall-Petch effect--the tendency for hardness to increase with decreasing grain size. Polycrystalline cBN materials are often synthesized by using the martensitic transformation of a graphite-like BN precursor, in which high pressures and temperatures lead to puckering of the BN layers. Such approaches have led to synthetic polycrystalline cBN having grain sizes as small as ∼14 nm (refs 1, 2, 4, 5). Here we report the formation of cBN with a nanostructure dominated by fine twin domains of average thickness ∼3.8 nm. This nanotwinned cBN was synthesized from specially prepared BN precursor nanoparticles possessing onion-like nested structures with intrinsically puckered BN layers and numerous stacking faults. The resulting nanotwinned cBN bulk samples are optically transparent with a striking combination of physical properties: an extremely high Vickers hardness (exceeding 100 GPa, the optimal hardness of synthetic diamond), a high oxidization temperature (∼1,294 °C) and a large fracture toughness (>12 MPa m(1/2), well beyond the toughness of commercial cemented tungsten carbide, ∼10 MPa m(1/2)). We show that hardening of cBN is continuous with decreasing twin thickness down to the smallest sizes investigated, contrasting with the expected reverse Hall-Petch effect below a critical grain size or the twin thickness of ∼10-15 nm found in metals and alloys.
Yongjun Tian; Bo Xu; Dongli Yu; Yanming Ma; Yanbin Wang; Yingbing Jiang; Wentao Hu; Chengchun Tang; Yufei Gao; Kun Luo; Zhisheng Zhao; Li-Min Wang; Bin Wen; Julong He; Zhongyuan Liu
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Nature     Volume:  493     ISSN:  1476-4687     ISO Abbreviation:  Nature     Publication Date:  2013 Jan 
Date Detail:
Created Date:  2013-01-17     Completed Date:  2013-03-04     Revised Date:  2013-10-24    
Medline Journal Info:
Nlm Unique ID:  0410462     Medline TA:  Nature     Country:  England    
Other Details:
Languages:  eng     Pagination:  385-8     Citation Subset:  -    
State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China.
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Comment In:
Nature. 2013 Oct 23;502(7472):E2-3   [PMID:  24153312 ]
Nature. 2013 Oct 23;502(7472):E1-2   [PMID:  24153311 ]

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