# Effect Of Oxidation With Aluminum Coating On The NY600 Carburization At 900 °C

Christophe Issartel, Henri Buscail, Sébastien Perrier

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Christophe Issartel, Henri Buscail, Sébastien Perrier. Effect Of Oxidation With Aluminum Coating On The NY600 Carburization At 900 °C. HTCPM 2024, Jun 2024, Ile des Embiez, Six Fours, France. hal-04832257

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Distributed under a Creative Commons Attribution 4.0 International License
# Effect Of Oxidation With Aluminum Coating On The NY600 Carburization At 900 °C

Christophe ISSARTEL<sup>a</sup>, Henri BUSCAIL<sup>a</sup>, Sébastien PERRIER<sup>a</sup>

<sup>a</sup>Université Clermont Auvergne - LVEEM, 3 Rue Lashermes, CS 10219, 43009 Le Puy-en-Velay, France
christophe.issartel@uca.fr; henri.buscail@uca.fr; sebastien.perrier@uca.fr

**Keywords** Oxidation, Aluminization, Alloy NY600, Carburization

## Introduction

Corrosion and carburization are the main reasons for the degradation of mechanical properties of conveyor units. In order to improve alloy carburization resistance, an adherent oxide scale can act as a carbon diffusion barrier. Oxidation of Alloy NY600 with aluminum coating in N₂ at 900 °C was performed in order to grow a protective and adherent alumina scale.

## Experimental

The NY600 alloy is an austenitic stainless steel. Table 1 gives the NY600 composition in weight %. 2 mm thick rectangular specimens (approximately 13 mm wide and 20 mm long) were abraded up to the 320-grit SiC paper, then degreased with ethanol and finally dried. Then, an aluminum CVD coating (100µm) was performed on NY600 specimens. A pre-oxidation was performed at 900 °C in N₂ on blank and coated samples. Carburization was performed at 900 °C in Ar-5vol.%CH₄ under atmospheric pressure for two hours.

<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

Figure 1 shows the kinetic curves obtained after isothermal oxidation of NY600 specimens at 900 °C, in N₂. For blank samples, the weight gain curves show a parabolic behavior during the 46 hours oxidation. A parabolic regime indicates the formation of a protective scale acting as a good diffusion barrier. The aluminization treatments decrease the weight gain.

<figure><img src="image_2.png" /><figcaption>Fig. 1 Mass gain versus time curves obtained after 46h isothermal oxidation of blank and aluminized NY600 in N₂ at 900 °C.</figcaption></figure>

## Morphology and oxide scale composition

The oxide scales cross sections are shown in figure 2. The oxide scales observed after pre-oxidation are adherent. On the NY600, the oxide scale is composed of chromia. Alumina is formed as internal oxide along the grain boundaries. On the aluminized NY600, the oxide scale is thin and composed of alumina. A thick NiAl coating is observed under the oxide scale and chromium is also present under the aluminum coating.
<figure><img src="image_3.png" /><figcaption>**Fig. 2** Oxide scale cross sections obtained after pre-oxidation (N₂, 900 °C, 46h) of NY600 and aluminized NY600 and after carburization (Ar-5vol.%CH₄, 900 °C, 2h) of the pre-oxidized samples.</figcaption></figure>

Carburization of pre-oxidized NY600 led to the formation of carbides at grain boundaries 100 µm deep inside the alloy. The aluminized NY600 sample has shown a good resistance against carburizing environments. These results are in qualitative accordance with the recent experimental investigations of Ortiz [1]

**Conclusion**

In order to improve alloy carburization resistance, an adherent oxide scale can act as a carbon diffusion barrier. Oxidation of aluminum coated Alloy NY600 in N₂ at 900 °C was performed to grow a protective and adherent alumina scale. This alumina/NiAl scale appears to be more protective than a chromia scale against carburization. Results indicate that a better performance in coking conditions can be attained using alumina-forming alloys.

**References**

1. L. Ortiz and B. Church, *Corrosion Science*, **190**, 1-11 (2021).