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# Water Vapor Influence on a Nickel-based Alloy NY600 Oxidation – Residual Stress Determination.

Henri Buscail, Christophe Issartel, Sébastien Perrier

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Henri Buscail, Christophe Issartel, Sébastien Perrier. Water Vapor Influence on a Nickel-based Alloy NY600 Oxidation – Residual Stress Determination.. HTCPM 2024, Jun 2024, Ile des Embiez, Six Fours, France. hal-04832254

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# Water Vapor Influence on a Nickel-based Alloy NY600 Oxidation – Residual Stress Determination

Henri BUSCAILª, Christophe ISSARTELª, Sébastien PERRIERª

ªUniversité Clermont Auvergne - LVEEM, 3 Rue Lashermes, CS 10219, 43009 Le Puy en Velay, France

henri.buscail@uca.fr; christophe.issartel@uca.fr; sebastien.perrier@uca.fr

**Keywords** Oxidation, Nickel-based alloy NY600, Water Vapor, Residual Stress, Cr₂O₃

## Introduction

The aim of this work is to show the influence of water vapour on the oxide scale formed in wet environment on a nickel-based alloys (NY600) between 900 and 1100 °C. Residual stress determinations were also performed after oxidation to characterise the influence of water vapor on the scale mechanical properties.

## Experimental

High temperature oxidation was performed during 96 h in flowing (8 l/h) air containing 10 vol.% H₂O. This gaseous environment corresponds to potential industrial oxidizing conditions. An adapted SETARAM TG92-1600 thermobalance was used to perform thermogravimetric measurements in dry and wet air. The oxide scale characterisation was realised by X-ray diffraction (XRD). XRD patterns were obtained by use of a PANalytical X'pert MPD diffractometer (copper radiation, λ = 0.15406 nm). SEM / EDS permit to analyse the oxide scale composition and morphology. The alloy composition is given in Table 1. Stress levels in Cr₂O₃ (ICDD 38-1479) were determined by X-ray diffraction. Determinations were made by using ψ goniometer technique, with Cr-Kα₁ = 0.229 nm radiation, based on the (86.42 ° 2θ) chromia peak [1, 2]. The ψ angle was varied in steps of 2 ° between -38 ° and +38 °. The mean stress σφ in the plane of the oxide is obtained from the slope (1 + v) σφ/E of the linear relationship between ε and sin²ψ, where ε is the strain, given by Δd/d, d being the interplanar spacing. The oxide was assumed to be isotropic with no stress gradients parallel to the surface components. The Cr₂O₃ Young's modulus, E, was taken as 282 GPa at room temperature and Poisson's ratio v as 0.30. The technique used is not able to determine the eventual stress gradient inside the oxide scale. Only a mean value is obtained from the whole surface and thickness analysed.

<table><caption>**Table 1.** NY600 Ni-based alloy composition (weight %).</caption><tr><td>NY600</td><td>Ni</td><td>Cr</td><td>Fe</td><td>Si</td><td>Ti</td><td>Mn</td><td>Al</td><td>Co</td></tr><tr><td>weight %</td><td>Bal.</td><td>15.8</td><td>8.5</td><td>0.32</td><td>0.27</td><td>0.87</td><td>0.22</td><td>0.04</td></tr></table>

## Kinetics

The mass gain curves per unit area are given in Fig. 1. All isothermal thermogravimetric analyses were carried out during 96 h at 900, 1000 and 1100 °C in ambient air and wet air (10 vol.% H₂O). A parabolic regime was observed throughout the 96 h oxidation tests. At 900 °C, the oxidation rates are similar under dry and wet air. At 1000 °C and 1100 °C, the oxidation rates are slightly higher in wet air than in dry air. No breakaway corrosion is observed within the 96 h isothermal oxidation tests.

<figure><img src="image_3.png" /><figcaption>**Fig. 1** Mass gain versus time curves obtained after 96h isothermal oxidation of NY600 under dry air and wet air (10 vol.% H₂O) at 900, 1000 and 1100 °C.</figcaption></figure>
## Morphology and oxide scale composition

The oxide scales cross sections are shown in figure 2. The oxide scales are adherent and mainly composed of chromia. A thin Mn<sub>1.5</sub>Cr<sub>1.5</sub>O<sub>4</sub> scale is found at the external interface mixed with some TiO<sub>2</sub> oxide grains. As also observed on other aluminium containing alloys (Inconel 601) [3] alumina is formed as internal oxide along the alloy grain boundaries. This internal aluminium oxidation seems to be deeper in wet conditions.

<figure><img src="image_4.png" /><figcaption>Fig. 2 Oxide scale cross sections obtained after dry and wet air (10 vol.% H<sub>2</sub>O) oxidation of NY600 between 900 and 1100 °C.</figcaption></figure>

## Conclusion

Between 900 and 1100 °C, 10 vol.% H<sub>2</sub>O in air has little effect on the NY600 stainless steel oxidation under isothermal conditions. The adherent oxide scale is mainly composed of Cr<sub>2</sub>O<sub>3</sub>. Some TiO<sub>2</sub> crystallites are observed at the external interface and Al<sub>2</sub>O<sub>3</sub> is present as internal oxide. Results show that water molecules do not influence the diffusion process in the scale formed on this nickel-based alloy. X-ray diffraction was used to determine the residual stress level in the chromia scale. Results show that on this substrate water vapor as no important influence on the stress level on the adherent chromia scale after oxidation. At 900°C σ = -800 +/- 100 MPa (dry) and σ = -900 +/- 100 MPa (wet). At 1000°C σ = -1800 +/- 100 MPa (dry) and σ = -1800 +/- 100 MPa (wet). At 1100°C σ = -2300 +/- 100 MPa (dry) and σ = -2200 +/- 100 MPa (wet). The alloy studied is believed to be an oxidation resistant material at high temperature in wet environments up to 1100 °C and 10 vol.% H<sub>2</sub>O. The role of Ti and Al will also be discussed.

## References

1. Chun. Liu. Analyse des contraintes par diffraction des rayons X à haute température dans le système Ni-NiO, Thèse de Doctorat, ENSAM Paris, 1991

2. F. Bernard, E. Sciora, N. Gerard, Experimental equipment for studying the residual stresses developed during high temperature reactions by X-Ray diffraction, *Journal de Physique*. IV, C4 (6) 259-266 (1996).

3. H. Buscail, S. Perrier, C. Josse, *Materials and Corrosion*. **62**, 5, 416-422 (2011).