Microstructure and Properties of TiAlN/a-C Nanocomposite Coatings Prepared by Reactive Sputtering

TiAlN/a-C nano-composite coatings were synthesized by a reactive co-sputtering process to investigate the effects of sputtering conditions on the microstructure and mechanical properties. Coating films were deposited on square plates of Si and high speed steel (ANSI M2) by the co-sputtering ofTiAl (pulsed-d.c. sputtering) and C (d.c. sputtering) targets using a "Facing Target-type Sputtering" system at an atmosphere with a mixture of Ar and N 2 but without hydrocarbon gas. The structure of the coatings was investigated by means of XRD, XPS and HRTEM with GIF (Gatan Imaging Filter). Mechanical properties of coating films were measured by a submicron indentation system. Though TiAlN and a-C coatings showed hardness of about 32 and about 10 GPa, respectively, TiAlN/a-C coatings containing 4.6 at% of C showed higher hardness of 43 GPa. The energy filter images depicted that a change of contrast in the zero-loss image corresponded to nanometer-size of Ti agglomerates in Ti map. Cls spectrum in XPS analysis revealed that carbon in the coatings was bounded as C-C and C-N without bonding of Ti-C or Al-C. These results indicated that the TiAlN/a-C nano-composite coatings consisted of complicated mixture of nanocrystalline Ti-Al-N phase and a-C phase (including C-N bonding).

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