Structural properties, internal stress and thermal stability of nc-TiN/a-Si3N4, nc-TiN/TiSix and nc-(Ti1-yAlySix)N superhard nanocomposite coatings reaching the hardness of diamond

A. Niederhofer, P. Nesládek, H. D. Männling, Keba Moto, S. Vepřek, M. Jílek

Research output: Contribution to journalArticlepeer-review

199 Citations (Scopus)

Abstract

The average crystallite size, d, in the range of about 3-8nm determined from XRD by means of the Scherrer formula and integral width of the Bragg peaks compares well with that determined from the Warren-Averbach analysis. TiN films show (200) texture which changes to random orientation of the crystallites when the silicon content reaches about 10 at.%. The biaxial stress of ≤0.4GPa for ≤10μm thick films is fairly low. The random stress determined from the Warren-Averbach analysis increases with decreasing crystallite size from about 1GPa for d ≥10nm to almost 10GPa for d≈3nm. A strong increase is observed for the stability of the nanostructure and of the hardness upon annealing: the recrystallization temperature increases from about 850°C for d≥5nm to ≥1150°C for d≤3nm. This is explained by thermodynamical stabilization of the grain boundaries due to segregation. Superhardness remains constant up to recrystallization. For superhardness of about 100GPa, the elastic modulus of 70-500GPa and the universal hardness of about 17-22GPa (loads between 30 and 100mN) compare well with the hardness of a single-phase nanocrystalline diamond. Besides this extremely high hardness, the coatings also have a very high toughness and elastic recovery of 80-90%.

Original languageEnglish
Pages (from-to)173-178
Number of pages6
JournalSurface and Coatings Technology
Volume120-121
DOIs
Publication statusPublished - 1 Jan 1999

Keywords

  • Hardness
  • Internal stress
  • Superhard nanocomposite coatings
  • Thermal stability

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