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In this study, SiO2 coating was electrodeposited on Ti45Al8.5Nb alloy to enhance its oxidation resistance at 900 °C. The focus was on the interaction between SiO2 coating and the alloy substrate, and specifically, the role of the Nb element in this context. The formation of a SiO2/(Ti, Nb)O2/Ti5Si3 + Al2O3 three-layer oxide scale significantly inhibits the inward diffusion of oxygen. Beyond the characteristic Ti5Si3 + Al2O3 layer at the interface, the Nb2Al phase embedded within Ti5Si3 was observed. Concurrently, the presence of a (Ti, Nb)O2 layer was confirmed. The relationship between the coating thickness and oxidation resistance was also investigated. It was found that the thickness of the SiO2 coating affects the density of the oxide scale and the inward diffusion rate of oxygen. Moreover, due to the good adhesion to the substrate, the derived oxide scale exhibited good anti-peeling performance when subjected to a cyclic oxidation test. [ABSTRACT FROM AUTHOR]

The low density, high specific strength, and good creep properties make TiAl alloys being promising high-temperature structural materials in aerospace and automotive industries. However, the insufficient oxidation resistance limits their extensive practical applications. It is the intention of this review to illustrate the mechanism and development of sol–gel-based coatings, a surface modification approach for oxidation protection of TiAl alloys, but not to present a general review on the oxidation protection of TiAl alloys. The oxidation behavior and mechanism of TiAl alloys were addressed briefly. The discussion focused mainly on the sol–gel coatings preparation method and generation mechanism. Finally, the development trend of sol–gel-based coatings for high-temperature oxidation of TiAl alloys was prospected. [ABSTRACT FROM AUTHOR]

A duplex composite coating consisting of electrodeposited SiO 2 interlayer and glass-ceramic coating was fabricated on TiAl alloy. The oxidation behavior of the composite coating was studied in air at 1000 °C. The composition, morphology, and microstructure of the oxide scale were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive spectroscopy (EDS). Results showed that the composite coating exhibited outstanding resistance against high temperature oxidation. After 100 h oxidation, no scale spallation was observed and the weight gain was only 1.16 mg cm−2. The inward diffusion of oxygen and outward diffusion of Ti were efficiently prevented. A continuous and adherent Al 2 O 3 layer was formed at the coating/substrate interface. The electrodeposited SiO 2 interlayer could improve the adhesion between the substrate and glass-ceramic coating. • Glass-ceramic coating and SiO 2 interlayer were fabricated on TiAl alloy. • SiO 2 interlayer can dissolve into the glass-ceramic coating and reduce its mobility. • The adhesion property of the glass-ceramic coating was enhanced. • The formation of nitride at the coating/substrate interface was suppressed. [ABSTRACT FROM AUTHOR]

• A glass-ceramic coating incorporated with YSZ and ZrB 2 was prepared. • An electrodeposited SiO 2 interlayer was introduced into the coating system. • The coating bulk and interfacial structures were both reinforced by the particles. • The coated TiAl alloy exhibited satisfactory oxidation resistance at 1000 ℃. With electrodeposited SiO 2 film as the interlayer, 8YSZ (8.0 wt.% Y 2 O 3 partially stabilized ZrO 2) and ZrB 2 particles co-incorporated glass-ceramic coating was fabricated on TiAl alloy. The oxidation performance and interfacial reaction behavior of this coating were studied. The compact glass-ceramic coating inhibited the inward diffusion of oxygen. The reaction between the SiO 2 interlayer and the potassium silicate coating benefited to improve the coating adhesion property and suppress the coating degradation at the coating/substrate interface. Due to the synergy of the incorporated particles and SiO 2 interlayer, both the oxidation performance and interfacial structure of the glass-ceramic coating were improved. [ABSTRACT FROM AUTHOR]

The influence of surface pretreatment on the oxidation performance of the anodized TiAl alloy was investigated. Before anodization in NH 4 F containing ethylene glycol, TiAl alloy was sand blasted or ground by SiC paper. Results showed that the humps on the rough surface serve as crystallographic templates for the nucleation of the isostructural α-Al 2 O 3 at the initial stage of oxidation. The derived Al 2 O 3 act as the crystal nuclei for the formation of continuous Al 2 O 3 oxide scale during thermal exposure, therefore providing good oxidation resistance. The surface roughness acts a key role to improve the oxidation resistance of the anodized TiAl alloy. • Surface roughness has a great influence on the oxidation resistance of anodized TiAl alloy. • Sand blasting results in a deformation zone and prompts the generation of Al 2 O 3. • The humps on the surface serve as templates for the nucleation of isostructural Al 2 O 3. • Surface roughness but not surface deformation acts a key role in the oxidation performance of anodized TiAl alloy. [ABSTRACT FROM AUTHOR]

Ni nanoparticle incorporated SiO 2 coating was fabricated on Ti48Al2Nb2Cr alloy by electro-codeposition. Results showed that the Ni-SiO 2 composite coating exhibits good isothermal and cyclic oxidation resistance at 900 ºC. The incorporation of Ni particles can adjust the coating thermal stress. After oxidation, no crack or pore can be found in the Ni-SiO 2 composite coating. The consumption of the inward diffused oxygen could reduce the oxygen partial pressure at the coating/substrate interface, therefore promoting the selective oxidation of Ti48Al2Nb2Cr to form Al 2 O 3. Owing to the good compatibility with SiO 2 , the oxidation product of NiO could strengthen the structure of the coating. [Display omitted] • The Ni-SiO 2 composite coating exhibits good isothermal and cyclic oxidation resistance. • The incorporated Ni particles can adjust the coating thermal stress and prevent the generation of cracks. • The inward diffused oxygen is consumed by the Ni particles, promoting the selected oxidation of Ti48Al2Nb2Cr to form α-Al 2 O 3. • The structure of the oxide scale can be improved by the oxide product of NiO. [ABSTRACT FROM AUTHOR]

The long-term isothermal oxidation and cyclic oxidation performance of the Ti48Al2Nb2Cr alloy anodized in NH 4 F containing electrolyte were investigated. After isothermal oxidation at 1000 °C and cyclic oxidation at 900 °C for 1000 h, the weight gains of the anodized Ti48Al2Nb2Cr alloys are 1.12 mg cm−2 and 0.48 mg cm−2, respectively. The excellent oxidation performance is ascribed to the fluorine effect. Raman and photo-stimulated luminescence spectra revealed that anodization impedes the formation of rutile and promotes the generation of α-Al 2 O 3 at high temperatures. The Al 2 O 3 and TiO 2 formed during anodization act as crystal nucleus for the generation of α-Al 2 O 3 -based scale. Al 2 O 3 and TiO 2 formed at the anodization process, together with the fluorine effect, promote the generation of protective α-Al 2 O 3 scale. [Display omitted] • A fluorine-enriched region can be found beneath the anodic film. • The anodized Ti48Al2Nb2Cr alloy exhibits excellent oxidation performance. • Al 2 O 3 and TiO 2 formed during anodization promote the generation of α-Al 2 O 3 -based scale. • The improved oxidation resistance can be ascribed to the fluorine effect. [ABSTRACT FROM AUTHOR]

• Ti45Al8.5Nb was anodized in NH 4 F containing solution. • Nb can reduce the critical Al content to form a continuous alumina layer. • The anodized Ti45Al8.5Nb exhibited excellent oxidation resistance at 1000 °C. • The improved oxidation resistance can be ascribed to halogen effect. Ti45Al8.5Nb was anodized in ethylene glycol and NH 4 F containing solution to improve the oxidation resistance. Isothermal oxidation test shows that the anodized specimens can provide excellent oxidation resistance and spallation resistance under 1000 °C. During the high temperature oxidation process, a compact and continuous alumina layer would generate on the anodized Ti45Al8.5Nb alloy. This protective alumina layer can efficiently decrease the inward diffusion of oxygen and outward diffusion of the substrate element. The improved oxidation resistance is assigned to the halogen effect caused by the fluorine component generated during the anodization process. [ABSTRACT FROM AUTHOR]

A novel Al–Si composite coating was fabricated on γ-TiAl by the combination of magnetron sputtered Al coating and subsequently electrodeposited SiO 2 coating. The oxidation performance of the specimens was evaluated in static air at 900 °C. Results shown that the Al–Si composite coating can act as an efficient oxygen migration barrier and provide good oxidation resistance. During the oxidation process, an Al 2 O 3 enriched layer formed beneath the composite coating. The interfacial reaction between the composite coating and alloy resulted in the generation of Al 2 O 3 and Ti 5 Si 3. Image 1 • A novel Al–Si composite coating was fabricated on γ-TiAl by a two-step method. • This Al–Si composite coating can prevent the formation of Al-depletion layer. • The interfacial reaction between the composite coating and alloy resulted in the generation of Al 2 O 3 and Ti 5 Si 3. • This Al–Si composite coating can reduce the coating/alloy interface hardness and improve the oxidation resistance. [ABSTRACT FROM AUTHOR]