On dipping of γ-TiAl in low-concentration phosphoric acid solution and consecutive oxidation resistance at 800°C

Brou, S.Y.; Siab, R.; Bonnet, Gilles; Grosseau-Poussard, Jean-Luc

doi:10.1016/j.scriptamat.2006.11.029

Cited by 8 publications

(9 citation statements)

References 24 publications

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“…Since their decomposition temperatures are well above 650°C, these compounds shall remain stable at our oxidation temperature of 650°C. Moreover, Brou et al [23][24][25] showed that the formation of metal pyrophosphates [AlxPyOz] could also occur. Depending on the temperature and time, the pyrophosphates evolve into Al2O3 and P2O5 [24].…”

Section: Cyclic Oxidation Tests On Aluminized and Aluminized/sealed Smentioning

confidence: 99%

“…on TiAl but at higher temperature [23][24][25], the phosphate layer seems to block diffusion, hence limiting oxidation while the growth of alumina would be delayed by the transformation of the aluminium phosphates. As a result, the oxide scales are much thinner than in the untreated specimens ( After more than 1000 cycles of exposure to air at 650°C, the microstructure and the composition of the sealed aluminide coatings remained similar to the untreated ones.…”

Section: Cyclic Oxidation Tests On Aluminized and Aluminized/sealed Smentioning

confidence: 99%

“…Sealing is commonly achieved by impregnating the coating with organic or inorganic solutions [20]. Orthophosphoric acid (H3PO4) and commercial phosphate solutions have been successfully used as sealants for porous oxide coatings [20][21][22] while mixed H3PO4 and acetone were employed to seal γ-TiAl [23][24][25]. With the latter, a gel-like deposit was left over the surface and the high temperature oxidation resistance in air was greatly improved.…”

Section: Introductionmentioning

confidence: 99%

“…shows the Raman spectra in different areas of the samples with 0.5 and 1 mol.L-1 concentrations and dipping time. Clearly, all the Raman peaks corresponded to the P-O vibration of H3PO4[23,24,33] while -Al2O3 was detected in the fluorescence region.…”

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confidence: 99%

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Suitable sealants for cracked aluminized austenitic steels and their oxidation behaviour

Boulesteix

Pedraza

2017

Surface and Coatings Technology

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Aluminizing of steels may result in the appearance of tensile cracks from the coating surface to the substrate due to the difference in thermal expansion coefficients. The cracks often need to be sealed to make the coatings impervious to chemical attack and to limit their mechanical degradation. In this work, dipping of the cracked aluminide coatings elaborated on IN-800HT in 0.5, 1 and 3.75 mol.L-1 concentrations of H3PO4 in acetone and increasing the dipping time are investigated. The three concentrations resulted in the formation of P-O compounds and of Al2O3. However, the 0.5 mol.L-1 allowed better wetting of the surface. Further reduction of the concentration from 0.5 mol.L-1 to 0.2 mol.L-1 brought about the complete sealing of both large and fine cracks. The efficiency of the sealing process with 0.2 mol.L-1 and 0.5 mol.L-1 was thereafter evaluated by cyclic oxidation in air at 650°C for more than 1000 cycles. The overall microstructure and composition of the aluminide coatings remained identical after sealing and the oxidation behaviour comparable to the untreated counterparts. The oxide scale formed on the untreated samples appeared thicker compared to the sealed ones. The latter were covered by a thin layer of AlPO4 which evolved towards a thin protective alumina scale. However, for the sealed samples, some minor cracks were detected after oxidation but they appeared completely healed with Al2O3 and no propagation of them beyond the additive layer/interdiffusion zone was noticed.

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Section: Cyclic Oxidation Tests On Aluminized and Aluminized/sealed Smentioning

confidence: 99%

Section: Cyclic Oxidation Tests On Aluminized and Aluminized/sealed Smentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Suitable sealants for cracked aluminized austenitic steels and their oxidation behaviour

Boulesteix

Pedraza

2017

Surface and Coatings Technology

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“…Unlike Ni-Al alloys, no protective Al 2 O 3 layer could occur on the titanium aluminide alloys because both titanium and aluminum form oxides of similar stability 11 . Therefore, many measures were taken to improve the oxidation resistance of titanium aluminide alloys such as surface treatment 12, 13 and coating technologies 14–16 . In particular, both mechanical properties and oxidation resistance at high temperatures can be simultaneously improved via adding moderate ternary or quartic elements such as niobium 17 , tungsten, silicon, molybdenum 18 , chromium 19 and yttrium 20 in binary titanium aluminide alloys 21, 22 .…”

Section: Introductionmentioning

confidence: 99%

Core-multishell globular oxidation in a new TiAlNbCr alloy at high temperatures

Shougao

et al. 2017

Sci Rep

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Oxidation resistance is one of key properties of titanium aluminide (TiAl) based alloys for high-temperature applications such as in advanced aero-engines and gas turbines. A new TiAlNbCr alloy with micro-addition of yttrium has been developed, but its oxidation behavior is unknown. To provide some fundamental insights, high-temperature oxidation characteristics of this alloy are examined via scanning electron microscopy, transmission electron microscopy, electron probe microanalysis, and X-ray diffraction. We show that distinctive core-multishell globular oxidation and “daisy” flower-like oxidation occur exclusively around Y2O3 particles. Globular oxides exhibit multi-layered Y2O3/TiO2/Al2O3-rich/TiO2-rich shell structures from the inside to outside. Flower-like inner oxides consist of core Y2O3 particles surrounded by divergent Al2O3 and oxygen-rich α2-Ti3Al in the near-scale substrate. As the scale-substrate interface moves inward, the inner oxide structures suffer deeper oxidation and transform into the globular oxide structures. Our results demonstrate that the unique oxidation characteristics and the understanding of formation mechanisms pave the way for the exploration and development of advanced oxidation-resistant TiAl-based materials.

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Microstructural evolution and high-temperature oxidation mechanisms of a titanium aluminide based alloy

Shougao

et al. 2018

Acta Materialia

130

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On dipping of γ-TiAl in low-concentration phosphoric acid solution and consecutive oxidation resistance at 800°C

Cited by 8 publications

References 24 publications

Suitable sealants for cracked aluminized austenitic steels and their oxidation behaviour

Suitable sealants for cracked aluminized austenitic steels and their oxidation behaviour

Core-multishell globular oxidation in a new TiAlNbCr alloy at high temperatures

Microstructural evolution and high-temperature oxidation mechanisms of a titanium aluminide based alloy

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