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Nanostructuring of functional ceramics by nano-assembling of stacking faults and twins

Alexander Taube* and Gregory Demyashev

Swinburne University of Technology
Melbourne VICTORIA 3122 Australia

This is an abstract for a presentation given at the
1st Conference on Advanced Nanotechnology:
Research, Applications, and Policy

 

New macroscopic properties of functional materials manifest themselves on nanometer-scale grain sizes, for example, by adding significantly to hardness of nanocomposites [1]. Usually nanostructuring elements of nanostructured materials are nano-scale grains (2-100 nm) divided by boundaries of ~1 nm thick.

The purpose of this report is to demonstrate a novel nanostructuring approach in order to obtain functional nanostructured materials that are based on self-assembling of both stacking faults (SFs) and nanoscale twins (NTs).

Sub-carbide and sub-nitride phases of transition metals such as Me4X3-type (Ta4C3, V4C3, (Ta,V)4C3, Hf4N3) and Me3X2-type (Ta3C2, V3C2, Ta2VC2, Hf3N2), where X=C or N, have attracted growing scientific interest primarily due to their unusual structure resulting from regularly ordered close packing, namely hexagonal close packing (hcp) and cubic close packing (ccp). It had been shown that a structure of the sub-phases is an alternation of Shockley stacking faults in {111}-planes resulting in two-phase ccp-hcp mixture on nano-scale range where three stacking faults are an inherent part of their lattice units. The tacking faults are crucial nanostructuring element of the sub-phases, which can be presented as a symbiosis of the stacking faults and their nanostructure. The basic domains, which make up the sub-phases nanostructured, are actuality nano-plates of approximately 1 nm thick. The nano-plates are divided by Shockley stacking faults the density of which can reach 1015-1016 cm-3.

The nanostructured sub-phases demonstrate incredible properties when comparing with carbides and nitrides having the same stoichiometry and the NaCl-type lattice. For example, the sub-phases of Ta4C3 and Hf4N3 at room temperature have microhardness of ~1.1 GPa and ~9 GPa respectively that is significantly softer in comparison with microhardness of TaC0.75 and NfN0.75 being as hard as ~13 GPa and ~16 GPa respectively.

Other properties of the nanostructured sub-phase of Ta4C3 such as absolute differential thermo-e.m.f., specific electrical resistance, breaking stress and yield strength were investigated in the temperature range of 300-2200 K. It was demonstrated that the properties of Ta4C3 and TaC0.75 substantially differ. The phase Ta4C3 is stable within the above-mentioned temperature range.

The role of SFs and NTs is vital in order to obtain such functional nanostructured ceramics. The self-organizing matter of SFs and NTs occurs if an appropriate stoichiometry of these functional ceramics is reached.

Reference

1. G.M. Demyashev, A.L. Taube, and E. Siores "Superhard Nanocomposites"- in: Encyclopedia of Nanoscience and Nanotechnology. Editor-in-Chief: H.S. Nalwa. American Scientific Publishers, Los Angeles (CA), vol. 10, p. 1-46. (www.aspbs.com/enn)

References

Abstract in Microsoft Word® format 26,950 bytes


*Corresponding Address:
Alexander Taube
Industrial Research Institute Swinburne at Swinburne University of Technology
PO BOX 218, Hawthorn, Melbourne VICTORIA 3122 Australia
Phone: 61 3 9214 5033 Fax: 61 3 9 214 5050
Email: ataube@swin.edu.au
Web: http://www.swin.edu.au/iris



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