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.