Microstructure and nanohardness properties of Zr–Al–N and Zr–Cr–N thin films

Thin films of zirconium based ternary transition metal nitrides Zr1−xMxN with M=Al, Cr were deposited on silicon, and WC–Co substrates by reactive magnetron sputtering. The chemical composition was measured by electron probe microanalysis. Cross-section transmission electron microscopy together with x-ray diffraction analysis showed that the films were solid solution single-phase fcc NaCl type of structure (B1). The columnar morphology, examined by transmission electron microscopy, does not change with increasing aluminum and chromium content. The stress-free lattice parameter of both coatings decreases linearly with x. With the increase of the Al content, the texture of the fcc–Zr1−xAlxN thin films progressively changes into randomly orientated, whereas that of Zr1−xCrxN remains unchanged. The nanohardness values gradually increase from Hn=21 up to 28 GPa as x increases from 0 to 0.43: the maximum hardness corresponds to a valence electron concentration =8.57 for x=0.43. In contrast, the hardness and Young’s modulus in Zr1−xCrxN remain nearly the same for all Cr contents.