Thermal plasma deposition of nanophase hard coatings

Thermal plasmas offer several specific advantages for the generation of hard coatings. In particular, the high energy density of the thermal plasma allows higher precursor flow rates and a wider choice of precursors. Expansion of the plasma into a low pressure chamber offers the additional advantages that improved control over the chemistry can be achieved or that nanosize particles can be generated. In this contribution, two experiments are described and the results reviewed in which supersonic plasma jets have been used to deposit nanophase hard coatings. In one of them, hard boron carbide coatings have been deposited using a supersonic plasma jet and a secondary discharge between the nozzle and the substrate. Spectroscopic analysis has been used to determine the reaction processes responsible for the deposition. In the other experiment, a plasma-containing silicon or titanium and carbon vapor has been expanded through a supersonic nozzle to form nanosize silicon or titanium carbide particles which are subsequently deposited on a substrate. Addition of a system of aerodynamic lenses allows the formation of a beam of nanosized particles which are deposited with high spatial definition. Narrow lines of a hard coating can thus be produced. In both processes, the deposition occurs rapidly, a fact which makes the processes attractive for a variety of potential applications.