A report on the potentials of laser chemical vapour deposition (LCVD) processes in the high temperature corrosion protection of automotive parts will be presented. Amorphous silica coatings are produced on metallic substrates by using an ArF excimer laser in parallel configuration to photolytically induce the reaction between SiH4 and N2O, using Ar as a buffer gas. Previously, all process parameters (SiH4/N2O ratio, total and partial pressures, substrate temperature, laser repetition rate, energy density and beam to the substrate distance) had been optimized for SiO2 deposition on Si wafers. It is shown that by tuning the laser beam to the substrate distance stoichiometric SiO2 films are deposited with different physico-chemical properties, namely refractive index, density and elastic modulus as determined by ellipsometry, FTIR, mass-volume measurements, nanoindentation, SEM, EDX and EMPA.
Corrosion tests of coated and uncoated Incoloy 800H samples have demonstrated that these LCVD silica coatings significantly improve the resistance of the metallic substrates to attack in aggressive atmospheres, even when submitted to thermal cycling. No sign of coating spalling or cracking was observed after nearly 2000 hours of exposure to the high temperature corrosion test.