Studies on the oxidation resistance of SiOC glasses coated TiAl alloy

Abstract

The purpose of the following work was to provide a performance evaluation of protective coatings based on silicon oxycarbide (Si-O-C) glasses (also known as “black glasses”), which act as a corrosion barrier on the TiAl alloy. A novel coating material was prepared by the sol-gel method with ladder-like polysilsesquioxanes as the precursors of black glasses. Alloy samples, which underwent a thoroughly defined surface preparation (grinding/polishing and degreasing), were dip-coated with synthesized sol. A series of structural studies (XRD, MIR, and EDS) was carried out to confirm whether black glass layers were obtained as a result of appropriate heat treatment consisting of drying and subsequent pyrolysis at 800 °C in an inert argon atmosphere. After an evaluation of the microstructure of coatings (SEM and Confocal microscopy), thermogravimetric analyses (TGA) were performed in laboratory air atmosphere at 800 °C for 100 h. The mass gain of coated samples was below 0.2 [mg/cm2] after 100 h, nearly one order of magnitude lower than that for the uncoated sample. After that, structural (XRD and EDS) and microstructural (SEM and Confocal microscopy) studies of surface and cross-section of samples were conducted. A comparison of structure and microstructure of oxidized, coated, and as-received specimens revealed a promising capability of black glass coatings to act as a protective layer for high-temperature corrosion.