C-metal (Ni, Ti) nanocomposite thin films were deposited by dc magnetron sputtering in argon between 25°C and 800°C onto SiO2 (300 nm) covered Si substrates in order to compare the structure- mechanical property relations in these films.
The structure of the films is quite similar due to the similarities of the growth mechanisms in the Ni-C and Ti-C systems. Below 400oC deposition temperature the films have two phase columnar structure, the columns being Ni3C or TiC crystallites of 5-50 nm in diameter and length, practically equal to the film thickness. The columnar crystallites are embedded into a few nm thick disordered a-C matrix, the ordering in which increases with increasing deposition temperature.
Measurements of the mechanical properties have shown that nanohardness of both kinds of films have the same dependence on the deposition temperature (Ts), namely display maximum at Ts=200oC (10-15 GPa). This behavior appears to be in connection with the structure and thickness of the amorphous carbon matrix.
The H/E ratio of 0.1 and elastic recovery of 0.5 indicate that the deformations of the films arise mainly from deformation of the matrix. As shown on film series prepared at low deposition temperature (25°C and 200°C) at various power of Ni target, the hardness of films was independent of metal content in the nanocomposite. On the contrary, the Young modulus shows a linear dependence on metal content of the films corresponding to the rule of mixtures.
Increasing of the growth temperature above 400oC brings about the thickening and graphite like ordering of the matrix and the change of Ni3C to fcc Ni in the crystalline phase. In Ti containing films the crystalline phase remains TiC, but the matrix undergoes similar changes to the case of C-Ni films. The structural changes are accompanied by the decrease of hardness and Young modulus in both systems.
Acknowledgment:
This work was supported in part by the European Community's Human Potential Programm under contract HPRN-CT-2002-00209, (New Fullerene-like Materials) and by the Hungarian National Science Foundation; OTKA T-043437 and 048699 projects. Katarina Sedlackova acknowledges the financial support of the HPRN-CT-2002-00209 project.
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