Phase stability and structural properties of Ti1-zZrzN (0<z<1) thin films

• Single-phase [NaCl]-structure Ti1-zZrzN thin films (0<z<1) have been deposited using cathodic arc plasma deposition. The films were investigated using X-ray diffraction, transmission electron microscopy, differential scanning calorimetry, and nanoindentation. Theoretical calculations on phase stabilities using density-functional theory revealed that the pseudo-binary TiN-ZrN system exhibits a miscibility gap, with respect to phase transformation from the as-deposited single-phase [NaCl] structure into [NaCl]-strueture TiN and ZrN components up to 980°C for z=0.35. The films were found to retain their as-deposited single-phase [NaCl] structure during post-deposition annealing for 120 min at 600, 700, 1100 and 1200°C, and for as long as 195 h at 600°C. This effective thermal stability is explained by a limited driving force for phase transformation and insufficient atom diffusivity. For two film compositions deepest within the miscibility gap, however, results from nanoindentation show an essentially retained hardness at ~30 GPa after annealing at 1100-1200°C. The principal hardening mechanism for the Ti1-zZrzN fihns is thus proposed to be solid-solution hardening through localized lattice strain fields originating from difference in atomic radius of Ti and Zr. This particular system offers interesting opportunities for fundamental studies of time-temperature-transformations of ternary nitride thin films.

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