Phase transformations in nanocomposite ZrAlN thin films during annealing
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s Ahlgren Sandvik Tooling AB, 126 80 Stockholm, Sweden
Jonathan Almer Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439
Lars Hultman Thin Film Physics, Department of Physics, Chemistry, and Biology (IFM), Linköping University, S-581 83 Linköping, Sweden
Magnus Odén Nanostructured Materials, Department of Physics, Chemistry, and Biology (IFM), Linköping University, S-581 83 Linköping, Sweden (Received 23 November 2011; accepted 16 March 2012)
Nanocomposite Zr0.52Al0.48N1.11 thin films consisting of crystalline grains surrounded by an amorphous matrix were deposited using cathodic arc evaporation. The structure evolution after annealing of the films was studied using high-energy x-ray scattering and transmission electron microscopy. The mechanical properties were characterized by nanoindentation on as-deposited and annealed films. After annealing in temperatures of 1050–1400 °C, nucleation and grain growth of cubic ZrN takes place in the film. This increases the hardness, which reaches a maximum, while parts of the film remain amorphous. Grain growth of the hexagonal AlN phase occurs above 1300 °C.
I. INTRODUCTION
Nanocomposite films consisting of one amorphous phase and one or more nanocrystalline phases can exhibit very high hardness. This has been explained by hindering of dislocation motion by the thin amorphous matrix surrounding the crystallites.1 Hard nanocomposites of several material systems have been studied, e.g., Ti–Si–N,1,2 Ti–Si–C–N,3,4 Zr–Si–N,5 and Ti–B–N.6,7 Such nanocomposites also retain their hardness at high temperatures since the grain growth is hindered by the amorphous matrix.8 Also two-phase nanocrystalline materials in the form of multilayers exhibit an increased hardness compared to their constituents due to the difference in elastic properties between the layers that hinder dislocation motion,9 most clearly seen in nanoscale multilayers.10,11 The decomposition of metastable single-phase films can also act to improve the hardness at elevated temperature as a two-phase structure is formed. The most studied of these is the TiAlN system where age hardening upon annealing of thin films was first observed.12,13 In the TiAlN system, the metastable cubic solid solution undergoes spinodal a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.122 1716
J. Mater. Res., Vol. 27, No. 13, Jul 14, 2012
http://journals.cambridge.org
Downloaded: 06 May 2016
decomposition during annealing into cubic domains enriched in TiN and AlN.14 The generated coherency strains between the domains and the difference in elastic properties between domains of different Al content15 hinder dislocation motion and thus increase the hardness. Following this example, age hardening during annealing has been observed for solid solution films of TiAlSiN,16 TiSiCN,17 TiBN,18 and TiAlCrN.19 The large miscibility gap of the ZrN–AlN system makes deposition of a solid solution possible only for low Al contents.20–23 AlN contents higher than 50 at.% result in a film consisti
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