Structural and mechanical stability upon annealing of arc-deposited Ti-Zr-N coatings

摘要

Ti-Zr-N coatings were formed by the method of vacuum arc deposition using combined Ti and Zr plasma flows in a N-2 atmosphere at different ratios of arc currents of Ti and Zr cathodes. After deposition, obtained samples were annealed in vacuum at the temperature of 850 degrees C. The element and phase composition, residual stresses and nanohardness were studied by Auger-Electron Spectroscopy, X-ray diffraction (XRD) and nanoindentation, respectively. XRD analysis reveals the formation of ternary Ti-Zr-N nitride coatings with the structure of solid solutions. It is shown that Ti-Zr-N coatings possess high hardness in comparison with TiN and ZrN binary nitrides. An increase in hardness is observed with increasing Zr content. However, it is established that after annealing coatings keep better stability of hardness with decrease of Zr content. The intrinsic stress in the as-deposited coatings is found to be largely compressive (-4 GPa) and almost independent of Zr content, but much higher than in ZrN and TiN binary nitrides (-2 GPa). After annealing, a significant stress relaxation is observed in all coatings due to relief of growth-induced point defects. Stress analysis on as-grown and annealed samples enabled us to determine the stress-free lattice parameter a(o). This latter is expanded by similar to 0.4-0.7% as compared to Vegard's law. The thermal stability of Ti-Zr-N coatings will be discussed in terms of evolution and interdependence between structure, composition and hardness after annealing. (C) 2007 Elsevier B.V. All rights reserved.