In order to prepare nanostructured carbon-tungsten films the original method called thermionic vacuum arc (TVA) [1] developed by our team was used. Two separate electron beams emitted by two externally heated cathodes (grounded tungsten filaments) accelerated by two high anodic voltages were directed toward graphite and tungsten anodes. Applying high voltages (1-5kV) between cathodes and respective anodes, bright plasmas in pure carbon and tungsten atoms were ignited simultaneously. The plasmas, monitorized by optical emission spectroscopy, were controlled independently by the electron beams emitted by the heated cathodes (thermoelectrons). We obtained hydrogen free nanostructured carbon-metal films with interesting properties as low friction and high wear rate in dry sliding. The process parameters were studied and optimized.
The prepared films were characterized by Raman and X-ray Photoelectron (XPS) spectroscopy, transmission electron and atomic force microscopy (TEM and AFM). Tribological properties in dry sliding were evaluated using a CSM ball-on-disc tribometer.
The carbon-tungsten films were identified as a nanocrystals complex (5 nm average diameter) surrounded by amorphous structures with a strong graphitization tendency. The Raman spectra showed typically D and G-bands of the amorphous carbon. By XPS were identified C-C (sp3 bonds) and C=C (sp2 bonds) depending on process parameters and carbon-tungsten relative concentrations. The coefficients of friction of the prepared films were in the range of 0.15-0.25 three to five times lower than the uncoated substrates.
References:
[1] C. P. Lungu, I. Mustata, G. Musa, A. M. Lungu, V. Zaroschi, K. Iwasaki, R. Tanaka, Y. Matsumura, I. Iwanaga, H. Tanaka, T. Oi, K. Fujita, Surf and Coat. Techn, 200, 399 (2005).
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