Assessment of ductile character in superhard Ta-C-N thin films

Research output: Contribution to journalArticleResearchpeer-review

Authors

  • Thomas Glechner
  • Rainer Hahn
  • Tomasz Wojcik
  • S. Kolozsvari
  • H. Zaid
  • S. Kodambaka

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 languageEnglish
Pages (from-to)17-25
Number of pages9
JournalActa materialia
Volume179.2019
Issue number15 October
Early online date10 Aug 2019
DOIs
Publication statusPublished - 15 Oct 2019