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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]

[Display omitted] • The precursor containing NiSO 4 and TEOS was applied to prepare Ni-SiO 2 coating. • The stress in the sintered Ni-SiO 2 coatings is reduced due to the incorporated Ni. • The Ni particles can withstand stress change and strengthen the coating structure. • The oxidation product of nickel, NiO, can impede the occurrence of cracking. In this study, a novel SiO 2 coating with the incorporation of nickel was prepared on Ti48Al2Nb2Cr alloy by co-electrodeposition. The effect of Ni in SiO 2 coating on the oxidation resistance of Ti48Al2Nb2Cr alloy at 900 °C was investigated. Due to the incorporation of nickel, the high temperature performance of the SiO 2 coating is promoted. For the Ni-modified SiO 2 coating, diffusion of oxygen to the substrate is effectively inhibited by a compact oxide scale composed of SiO 2 outer layer, Al 2 O 3 middle layer, and Ti 5 Si 3 inner layer. The incorporated Ni reinforces the structure and withstands the stress change of the SiO 2 coating. Moreover, the occurrence of cracking is impeded by NiO which is formed during oxidation. [ABSTRACT FROM AUTHOR]

SiOC coating was electrodeposited on TiAl alloy to improve the high temperature oxidation resistance. The mass gain of the compact SiOC coating is 0.06 ± 0.026 mg cm-2, which is one order of magnitude lower than that of TiAl alloy. The SiOC coating exhibits good thermal stability and partial amorphous SiOC transforms into crystal SiO 2 or SiC. After oxidation, no obvious pore can be found in the coating. Moreover, an Al 2 O 3 layer is generated due to the enrichment of Al and the low oxygen partial pressure at the coating/substrate interface, therefore improving the barrier property of the oxide scale. [Display omitted] • SiOC coating is prepared on TiAl alloy by electrodeposition. • The high temperature oxidation resistance of the TiAl alloy with the SiOC coating is dramatically improved. • Thermal exposure results in partial amorphous SiOC transforms into crystal SiO 2 or SiC. • The outward diffused Al can strengthen the network structure of the SiOC coating and establish an Al 2 O 3 intermediate layer. [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]