Assessment of ductile character in superhard Ta-C-N thin films
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Authors
Organisational units
External Organisational units
- Plansee Composite Materials GmbH
- Department of Nuclear Engineering, University of California Berkeley
- Institute of Materials Science and Technology
Abstract
Using a combination of density functional theory calculations and nanomechanical testing of sputter-deposited, 110-oriented Ta 0.47C 0.34N 0.19 thin films, we show that non-metal alloying – substituting C with N atoms – in TaC results in a super-hard material with enhanced ductility. Based on the calculated elastic constants, with Pugh and Pettifor criteria for ductile character, we predict that stoichiometric and sub-stoichiometric Ta-C-N alloys are more ductile than Ta-C compounds. From nanoindentation of the as-deposited coating, we measure hardness of 43 ± 1.4 GPa. In situ scanning electron microscopy (SEM) based micro-compression of cylindrical pillars, prepared via focused ion beam milling of the coating, revealed that Ta-C-N alloys are ductile and undergo plastic deformation with a yield strength of 17 ± 1.4 GPa. The post-compression SEM images of the pillars show {111} <011¯> as the active slip system operating during compression. Additional in situ SEM based cantilever tests suggest that the Ta-C-N films exhibit superior fracture toughness compared to Ta-C coatings. Our results provide a new perspective on the role of alloying on the mechanical behavior of ultra-high temperature compounds such as transition-metal carbides.
Details
Original language | English |
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Pages (from-to) | 17-25 |
Number of pages | 9 |
Journal | Acta materialia |
Volume | 179.2019 |
Issue number | 15 October |
Early online date | 10 Aug 2019 |
DOIs | |
Publication status | Published - 15 Oct 2019 |