Thermal plasma deposition of nanophase hard coatings

Thermal plasmas offer several specific advantages for the generation of har d coatings. In particular, the high energy density of the thermal plasma al lows higher precursor flow rates and a wider choice of precursors. Expansio n of the plasma into a low pressure chamber offers the additional advantage s that improved control over the chemistry can be achieved or that nanosize particles can be generated. In this contribution, two experiments are desc ribed and the results reviewed in which supersonic plasma jets have been us ed to deposit nanophase hard coatings. In one of them, hard boron carbide c oatings have been deposited using a supersonic plasma jet and a secondary d ischarge between the nozzle and the substrate. Spectroscopic analysis has b een used to determine the reaction processes responsible for the deposition . In the other experiment, a plasma-containing silicon or titanium and carb on vapor has been expanded through a supersonic nozzle to form nanosize sil icon or titanium carbide particles which are subsequently deposited on a su bstrate. Addition of a system of aerodynamic lenses allows the formation of a beam of nanosized particles which are deposited with high spatial defini tion. Narrow lines of a hard coating can thus be produced. In both processe s, the deposition occurs rapidly, a fact which makes the processes attracti ve for a variety of potential applications. (C) 2001 Elsevier Science B.V. All rights reserved.