Comparison of structure and properties of SiOx coatings deposited by reactive pulsed magnetron sputtering (PMS) and by hollow cathode activated EB evaporation (HAD)

The structure and properties of SiOx coatings deposited by reactive pulsed magnetron sputtering (PMS) and by hollow cathode activated electron beam (EB) evaporation (HAD) were investigated. Dense and nearly stoichiometric SiO2 coatings can be obtained by reactive PMS at deposition rates of approximately 5 nm/s. The coatings exhibit a high hardness of 8 GPa and a Youngʹs Modulus of 70 GPa, which are comparable with the bulk quartz glass. The deposition of SiOz coatings by HAD process enables high deposition rates of approximately 600 nm/s and therefore a very high productivity. By additional introduction of the monomer hexamethyldisiloxane (HMDSO) in vapor stream the structure and the properties of the coatings are modified by partial incorporation of organic components. With increasing HMDSO inlet the hardness is reduced from approximately 4.1 to 1.7 GPa and the Youngʹs modulus decreases from approximately 42 to 15 GPa, respectively. These comparably low hardness values are caused by microporosity and by incorporation of organic components in the coatings. Despite the low hardness, the coatings exhibit a very high abrasion resistance comparable with float glass. It seems that for abrasive wear the lower hardness of SiOx coatings deposited by the HAD process is compensated by a higher fracture toughness. The microporosity and the organic portion in the coatings probably cause a higher dispersion of crack energy and therefore a higher abrasion resistance.