CERAMIC COATINGS FOR HIGH-TEMPERATURE CORROSION PROTECTION BY LASER-CVD PROCESSES

In this paper we report the potentials of laser chemical vapour deposi tion (laser-CVD) processes in the high-temperature corrosion protectio n field. Amorphous silica coatings are produced on metallic substrates by using an ArF excimer laser in parallel configuration to photolytic ally induce the reaction between SiH4 and N2O, using Ar as a buffer ga s. It is shown that by tuning the laser beam to the substrate distance stoichiometric SiO2 films are deposited with different physico-chemic al properties, namely refractive index, density and elastic modulus as determined by ellipsometry, FTIR, mass-volume measurements, nanoinden tation, SEM, EDAX and EMPA. Corrosion tests of coated and uncoated Inc oloy 800H samples have demonstrated that these LCVD silica coatings si gnificantly improve the resistance of the metallic substrates to corro sive attack in aggressive atmospheres, even when submitted to thermal cycling. No sign of coating spalling or cracking was observed after ne arly 2000 hours of exposure to the high-temperature corrosion test.