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<p>The strength of refractory ceramics is much limited by their brittleness. Counterintuitively, we observe simultaneous high hardness and metallic-like ductility in highly overstoichiometric single-crystal HfN<sub>1.22</sub> and HfN<sub>1.33</sub> films grown by ion-assisted reactive magnetron sputtering. Here, we show by electron microscopy, diffraction methods, and ab-initio calculations the existence of a superstructure ordering of metal vacancies and nitrogen interstitials into sub-nanometer hyper-overstoichiometric and quasi-stoichiometric domains that self-organize into a checkerboard pattern superimposed onto the NaCl-structured lattice. A high intrinsic dislocation density and low dislocation nucleation barrier on {111} &lt; 011&gt; slip systems enable extraordinary ductility and strain hardening at &gt;50% strain, in room temperature uniaxial compression of HfN<sub>1.22</sub> micropillars. The films simultaneously exhibit a high hardness – tunable up to 28 GPa via control of stoichiometry – and a remarkable fracture resistance due to dislocation-mediated stress dissipation. The presented findings provide a route for synthesizing nitride superstructured films with unique hardness/toughness combinations.</p>

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Metal-like ductility and high hardness in nitrogen-rich HfN thin films by point defect superstructuring

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年3月13日

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  • Marcus Lorentzon,
  • Davide G. Sangiovanni,
  • Naoki Takata,
  • Tianqi Zhu,
  • Rainer Hahn,
  • Justinas Palisaitis,
  • Lars Hultman,
  • Jens Birch,
  • Naureen Ghafoor

摘要

The strength of refractory ceramics is much limited by their brittleness. Counterintuitively, we observe simultaneous high hardness and metallic-like ductility in highly overstoichiometric single-crystal HfN1.22 and HfN1.33 films grown by ion-assisted reactive magnetron sputtering. Here, we show by electron microscopy, diffraction methods, and ab-initio calculations the existence of a superstructure ordering of metal vacancies and nitrogen interstitials into sub-nanometer hyper-overstoichiometric and quasi-stoichiometric domains that self-organize into a checkerboard pattern superimposed onto the NaCl-structured lattice. A high intrinsic dislocation density and low dislocation nucleation barrier on {111} < 011> slip systems enable extraordinary ductility and strain hardening at >50% strain, in room temperature uniaxial compression of HfN1.22 micropillars. The films simultaneously exhibit a high hardness – tunable up to 28 GPa via control of stoichiometry – and a remarkable fracture resistance due to dislocation-mediated stress dissipation. The presented findings provide a route for synthesizing nitride superstructured films with unique hardness/toughness combinations.