Protective Si–Al–O–Y glass coatings on stainless steel in situ prepared by combustion flame spraying

Surface treatments are a common solution for reducing wear and friction, as well as for increasing oxidation and corrosion resistances. Two refractory glass compositions in the SiO2–Al2O3–Y2O3 system have been in situ deposited on AISI 304 stainless steel substrates by combustion flame spraying, with an oxyacetylene torch. Both compositions, 66SiO2–22Al2O3–12Y2O3 mol.% (G) and 50SiO2–30Al2O3–20Y2O3 mol.% (D), were formulated in the glass forming area; however, G is situated in the pure glass zone and D in a zone of glass formation where partial crystallizations occur. As-sprayed coatings had a thickness of 150–240 μm and were of glassy nature, although in D composition formation of Y3Al5O12 and Y2Si2O7 phases was observed. The influence of the Si/Al/Y ratios on the microstructure and properties of the coatings has been studied by scanning electron microscopy/energy-dispersive spectrometry (SEM-EDS), X-ray diffraction (XRD) and microhardness indentation tests. Properties of these coatings were compared to the bulk properties of the same composition glasses finding direct relationships between them.