TY - JOUR

T1 - Assessment of ductile character in superhard Ta-C-N thin films

AU - Glechner, Thomas

AU - Hahn, Rainer

AU - Wojcik, Tomasz

AU - Holec, David

AU - Kolozsvari, S.

AU - Zaid, H.

AU - Kodambaka, S.

AU - Mayrhofer, Paul Heinz

AU - Riedl, Helmut

PY - 2019/10/15

Y1 - 2019/10/15

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=85070920570&partnerID=8YFLogxK

U2 - 10.1016/j.actamat.2019.08.015

DO - 10.1016/j.actamat.2019.08.015

M3 - Article

VL - 179.2019

SP - 17

EP - 25

JO - Acta materialia

JF - Acta materialia

SN - 1359-6454

IS - 15 October

ER -