Characterization of tungsten-carbon layers deposited on stainless steel by reactive magnetron sputtering
- PDF / 5,632,683 Bytes
- 10 Pages / 576 x 792 pts Page_size
- 46 Downloads / 209 Views
Tungsten-carbon coatings have been deposited on stainless steel substrates by reactive magnetron sputtering from Ar-CH 4 mixtures. The carbon concentration in the coatings measured by electron microprobe analyses was found to be proportional to the CH4 flow rate. Only the cubic a - W phase with a dilated lattice parameter was identified in W - C coatings having a carbon content lower than 25 at. %. Since the lattice parameter of the a - W phase in these W - C coatings increased with increasing carbon content, these coatings may be assumed to be W - C solid solutions. Only the nonstoichiometric fi-WCi-x carbide (cubic phase) was detected in W - C coatings containing 30 to 70 at.% of carbon. The chemical state of the elements was investigated by x-ray photoelectron spectroscopy. The Vickers hardness of the W - C coatings was found to be considerably dependent on the carbon concentration. A maximum microhardness of 26 000 MPa was measured for W - C coatings containing either 14-15 at. % or 40-45 at. % of carbon. The correlation between crystallographic structure and microhardness is analyzed and discussed in this paper.
I. INTRODUCTION Various physical or chemical vapor deposition methods have been investigated to produce tungsten carbide, tungsten-carbon alloys, or tungsten carbide with additive (cobalt) used as hard and protective coatings.1 Relatively few attempts were directed toward the deposition of W - C coatings by reactive sputtering although this method was successfully applied to deposit a large variety of compounds with a wide range of properties difficult or impossible to obtain by other means.2 Tungsten-carbon layers with a carbon concentration higher than 40 at. % have been reactively sputter deposited in an argon-acetylene plasma from either a W target using radio frequency (r.f.), as direct current (d.c.) magnetron sputtering systems,3"10 or a WC target using r.f. diode sputtering equipment.11 The structure, morphology, and mechanical properties (microhardness, friction coefficient, wear resistance) were investigated as functions of the substrate temperature. 37 A mixture of tungsten carbides, namely f3-WCi-x (cubic phase), a - W 2 C (hexagonal phase), and W 3 C (cubic phase) was obtained at a substrate temperature of 200 °C whereas, at higher temperatures, only the nonstoichiometric /3-WCi- x tungsten carbide was formed. Sputtered W - C layers with a carbon concentration varying from few at. % to about 40 at. % seem to be rather difficult to synthesize by using an Ar-C 2 H 2 plasma; indeed, the amount of carbon in the deposited material was found to
a>Institut
National Polytechnique de Grenoble, ENSEEG, B.P. 75, 38402 Saint Martin d'Heres, France.
2070 http://journals.cambridge.org
J. Mater. Res., Vol. 7, No. 8, Aug 1992 Downloaded: 14 Mar 2015
be about 46 at. % with a flow rate of acetylene injected in the sputtering chamber as low as 3 standard cm 3 /min. 9 This difficulty may originate from the low stability of C 2 H 2 and could be overcome by using a carbon precursor more stable than acetyl
Data Loading...
