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Амирханова, Н. А.; Nev’yantseva, R. R.; Быбин, А. А.; Semenova, Irina P.; Smolnikova, O. G.

doi:10.1023/a:1025807105304

Cited by 4 publications

(3 citation statements)

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“…On the other hand, such a combination of acids should be safe for the surfaces of substrates. Considering the requirements above, many acids and inorganic reagents, such as (NH 4 ) 6 Mo 7 O 24 , HNO 3 , HF and HCl, and their combinations, have been adopted [11][12][13][14]. Poupard et al investigated various soft chemical stripping methods and found that chemical baths containing relatively high concentrations of pitting reagents in organic media are the most effective [15].…”

Section: Introductionmentioning

confidence: 99%

In-Depth Understanding of the Chemical Stripping Mechanism of AlSiY Coatings on Nickel Superalloys by First-Principles Calculation

Li,

Luo,

Zhang

et al. 2024

Coatings

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In order to repair a failed AlSiY coating on aeroengine turbine components, the AlSiY coating was stripped using a nitric acid-based removal reagent. The homogeneity of chemical stripping was evaluated and the stripping mechanism was clarified using first-principles calculations. The effects of hydrofluoric acid (HF) and chromium trioxide (CrO3) on the homogeneity of chemical stripping were investigated by calculating the electronic work functions (EWFs) of the stripped surfaces. The results showed that the stripped surfaces of the AlSiY coating exhibited a serrated appearance when it was etched by a single nitric acid solution, indicating severely inhomogeneous stripping. With the addition of HF and/or CrO3, the homogeneity of chemical stripping could be greatly improved, which was attributed to the increased EWF of the (200) surface and the decreased EWF of the (110) surface, causing the corrosion cathode to transition from the (110) surface to the (200) surface. The HF+CrO3+HNO3 mixed reagent was the optimal combination for the uniform stripping of the AlSiY coating, while the inner layer was not broken. The Al atoms on the surface could be preferentially removed due to the strong bonding with acid ions. The research method proposed in the present work will provide a new means to design chemical removal reagents.

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Section: Introductionmentioning

confidence: 99%

In-Depth Understanding of the Chemical Stripping Mechanism of AlSiY Coatings on Nickel Superalloys by First-Principles Calculation

Li,

Luo,

Zhang

et al. 2024

Coatings

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“…Chemical stripping generally involves the use of strong inorganic acids that may reduce the substrates cross-section, hence compromising the mechanical properties of the component. For the specific case of aluminide coatings, Amirkhanova and Nev'yantseva [3] employed a mixture of nitric and hydrochloric acids (2:1) to which potassium dichromate and ammonium heptamolybdate were added to increase the oxidising power. Nevertheless, the presence of NH 4 + , Mo 7 O 24 6-and Cr 2 O 7 2-ions represents non negligible environmental hazards [4].…”

Section: -Introductionmentioning

confidence: 99%

Soft chemical stripping of aluminide coatings and oxide products on Ni superalloys

Poupard¹,

Martínez²,

Pedraza³

2008

Surface and Coatings Technology

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“…HF, HNO 3 ) that may degrade the superalloy substrate [e.g. 18,19]. Furthermore, most of these chemicals are toxic and carcinogenic [20].…”

Section: Introductionmentioning

confidence: 99%

Controlled stripping of aluminide coatings on nickel superalloys through electrolytic techniques

et al. 2008

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Aluminide diffusion coatings are widely employed to improve the oxidation and/or the corrosion resistance of highly added value turbine components operating in harsh environments at high temperatures. Refurbishment of such components requires appropriate removal of worn coatings and of the corrosion products layer-usually an oxide scale. Stripping is mostly carried out using hazardous chemical baths of limited reliability. In this work, an alternative stripping method based on electrochemical techniques has been carried out at laboratory scale for CVD Al diffusion coatings on a directionally solidified Ni base superalloy. Both the galvanostatic and the potentiostatic modes have been investigated. Prior to them, in situ gas bubbling induced by cathodic polarization seems to be an effective way to remove the superficial oxide scales. Measuring the open circuit potential during the experiments allows easy monitoring of the progress of the selective dissolution of the different layers. Complete removal of the aluminide coatings is indicated by potential values similar to those of the substrate. The correlation between the electrochemical features and the surface state after stripping has been carried out by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). The electrochemical approach is a promising means to strip out surfaces in a selective and reliable manner.

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Cited by 4 publications

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In-Depth Understanding of the Chemical Stripping Mechanism of AlSiY Coatings on Nickel Superalloys by First-Principles Calculation

In-Depth Understanding of the Chemical Stripping Mechanism of AlSiY Coatings on Nickel Superalloys by First-Principles Calculation

Soft chemical stripping of aluminide coatings and oxide products on Ni superalloys

Controlled stripping of aluminide coatings on nickel superalloys through electrolytic techniques

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