# Hot corrosion of platinum-containing TROPEA superalloy

Louis Hunault, Stéphane Mathieu, Lionel Aranda, Jonathan Cormier, Renaud Podor, Fernando Pedraza

► To cite this version:

Louis Hunault, Stéphane Mathieu, Lionel Aranda, Jonathan Cormier, Renaud Podor, et al. Hot corrosion of platinum-containing TROPEA superalloy. Workshop Molten Salts & Extreme Environments, Mar 2025, Lanzarote, Spain. hal-05339164

HAL Id: hal-05339164

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<figure><img src="image_1.png" /></figure>

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# Hot corrosion of platinum-containing TROPEA superalloy

Lanzarote 2025 – Lanzarote, Canary Islands, SPAIN

21 March 2025

Louis HUNAULT*, Stéphane MATHIEU**, Lionel ARANDA**, Jonathan CORMIER***, Renaud PODOR****, Fernando PEDRAZA*

**Email: louis.hunault@univ-lr.fr, stephane.mathieu@univ-lorraine.fr, lionel.aranda@univ-lorraine.fr
renaud.podor@cea.fr; jonathan.cormier@ensma.fr; fernando.pedraza@univ-lr.fr

* Université de La Rochelle. LaSIE UMR 7356-CNRS. 17042 La Rochelle cedex 1. France

**Institut Jean Lamour, Campus Artem, 2 allée André Guinier 54011 Nancy. France

***Institut Pprime, 1 avenue Clément ADER 86961 Chasseneuil – Futuroscope. France

****Institut de Chimie Séparative de Marcoule ICSM, Site de Marcoule, Bâtiment 426 30207 Bagnols sur Cèze. France
<figure><img src="image_2.png" /></figure>
<figure><img src="image_3.png" /><figcaption>Flight: A320
Aircraft engines: CFM56-5B</figcaption></figure>

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>
<figure><img src="image_6.png" /></figure>

Sulfur species : Troposphere (1.10⁻⁵ and 0.07ppm) + Jet-A1 fuel (400-800ppm)

NaCl (g)

Turbine

<figure><img src="image_7.png" /></figure>

Flight: A320

Cold section
(<500°C)

Hot section
(500-1100°C)

Aircraft engines: CFM56-5B

<figure><img src="image_8.png" /></figure>

$$4 \text{ NaCl(g)} + 2 \text{ H}_2\text{O(g)} + 2 \text{ SO}_2\text{(g)} + \text{O}_2\text{(g)} \rightarrow 2 \text{ Na}_2\text{SO}_4\text{(s)} + 4 \text{ HCl(g)}$$

Atmosphere

<figure><img src="image_9.png" /></figure>

<figure><img src="image_10.png" /></figure>

Atmosphere + fuel

<figure><img src="image_11.png" /></figure>

$$T > T_m(\text{Na}_2\text{SO}_4) = 884 \, ^\circ\text{C}$$

Type I hot corrosion

<figure><img src="image_12.png" /></figure>
Type-I Hot Corrosion: $T > T_m (Na_2SO_4) = 884^\circ C$

1. Incubation + initiation stage

Simple oxidation + diffusion of sulfur through the
oxide layer

2. Propagation stage

Dissolution of oxides and re-precipitation in porous
oxide layer

accelerated degradation → Basic and Acidic Fluxing
Type-I Hot Corrosion: T > Tm (Na₂SO₄) = 884°C

1. Incubation + initiation stage

Simple oxidation + diffusion of sulfur through the
oxide layer

2. Propagation stage

Dissolution of oxides and re-precipitation in porous
oxide layer

accelerated degradation → Basic and Acidic Fluxing

$$
\mathrm{Na_2SO_4 \rightarrow Na_2O + SO_3}
$$

<figure><img src="image_13.png" /></figure>

Type I hot corrosion behavior of TROPEA?
Ni-Based single crystal superalloy: TROPEA and CMSX-4

<figure><img src="image_14.png" /></figure>

Y

Y'

<table><thead><tr><th></th><th></th><th>Ni</th><th>Cr</th><th>Mo</th><th>Co</th><th>W</th><th>Re</th><th>Al</th><th>Ti</th><th>Ta</th><th>Pt</th><th>Hf</th></tr></thead><tbody><tr><td>CMSX-4</td><td>wt.%</td><td>Bal.</td><td>6.4</td><td>0.6</td><td>9.7</td><td>6.4</td><td>2.9</td><td>5.6</td><td>1.1</td><td>6.5</td><td>/</td><td>0.1</td></tr><tr><td>TROPEA</td><td>wt.%</td><td>Bal.</td><td>6.5</td><td>0.6</td><td>9.0</td><td>6.0</td><td>1.0</td><td>5.6</td><td>1.0</td><td>9.0</td><td>2.0</td><td>0.1</td></tr></tbody></table>

<figure><img src="image_15.png" /></figure>

<figure><img src="image_16.png" /></figure>

<figure><img src="image_17.png" /></figure>

<figure><img src="image_18.png" /></figure>

<figure><img src="image_19.png" /></figure>

Pt effects:

* Stabilize γ' precipitates near the solvus temperature

* TROPEA exhibits excellent fatigue properties at 1200°C

* Creep strength and high yield stress similar to 2nd and 3rd generation superalloys
Y

Y'

<table><thead><tr><th></th><th></th><th>Ni</th><th>Cr</th><th>Mo</th><th>Co</th><th>W</th><th>Re</th><th>Al</th><th>Ti</th><th>Ta</th><th>Pt</th><th>Hf</th></tr></thead><tbody><tr><td>CMSX-4</td><td>wt.%</td><td>Bal.</td><td>6.4</td><td>0.6</td><td>9.7</td><td>6.4</td><td>2.9</td><td>5.6</td><td>1.1</td><td>6.5</td><td>/</td><td>0.1</td></tr><tr><td>TROPEA</td><td>wt.%</td><td>Bal.</td><td>6.5</td><td>0.6</td><td>9.0</td><td>6.0</td><td>1.0</td><td>5.6</td><td>1.0</td><td>9.0</td><td>2.0</td><td>0.1</td></tr></tbody></table>

* CMSX-4 more homogeneous γ/γ' microstructure than TROPEA

* Both superalloys contain casting pores and Laves phases

CMSX-4

<figure><img src="image_20.png" /></figure>

Dendrites region

TROPEA

<figure><img src="image_21.png" /></figure>

Eutectic (interdendritic region)

Pores

<figure><img src="image_22.png" /></figure>

<figure><img src="image_23.png" /></figure>

Laves phase

<figure><img src="image_24.png" /></figure>

<figure><img src="image_25.png" /></figure>
# Type I hot corrosion behavior of TROPEA?
**In air:**

* Temperature: 900°C

* Time: 24 h

* Deposit: 1 ± 0.5mg/cm² of Na₂SO₄ by aerograph

<figure><img src="image_26.png" /></figure>

**In air + 400 ppm of SO₂:**

* Temperature: 900°C

* Time: 24 h

* Deposit: 1 ± 0.5mg/cm² of Na₂SO₄ by aerograph

<figure><img src="image_27.png" /></figure>

**Analytical techniques:**

* TGA, Optical microscopy, SEM-EDS, XRD, Raman spectroscopy
<figure><img src="image_28.png" /></figure>
<figure><img src="image_29.png" /></figure>

<figure><img src="image_30.png" /></figure>

Only initiation stage
<figure><img src="image_31.png" /></figure>

<table><thead><tr><td></td><td>k<sub>p</sub> (mg<sup>2</sup>.cm<sup>-4</sup>.s<sup>-1</sup>)</td></tr></thead><tbody><tr><td>CMSX-4</td><td>1.8x10<sup>-6</sup></td></tr><tr><td>CMSX-4 + Na<sub>2</sub>SO<sub>4</sub></td><td>1.7x10<sup>-7</sup></td></tr></tbody></table>

<figure><img src="image_32.png" /></figure>

Only initiation stage

<table><thead><tr><td></td><td>k<sub>p</sub> (mg<sup>2</sup>.cm<sup>-4</sup>.s<sup>-1</sup>)</td></tr></thead><tbody><tr><td>CMSX-4 + Na<sub>2</sub>SO<sub>4</sub></td><td>1.7x10<sup>-7</sup></td></tr><tr><td>TROPEA + Na<sub>2</sub>SO<sub>4</sub></td><td>5.4x10<sup>-7</sup></td></tr></tbody></table>
in air

<figure><img src="image_33.png" /></figure>

Only initiation stage

in air with 400 ppm of SO₂

<figure><img src="image_34.png" /></figure>
in air

<figure><img src="image_35.png" /></figure>

Only initiation stage

in air with 400 ppm of SO₂

<figure><img src="image_36.png" /></figure>

TROPEA: Initiation and propagation stage

CMSX-4: Initiation stage
Kinetics study

<table><thead><tr><th>TROPEA</th><th>k<sub>p</sub> (mg<sup>2</sup>.cm<sup>-4</sup>.s<sup>-1</sup>)</th></tr></thead><tbody><tr><td>In air</td><td>5.4x10<sup>-7</sup></td></tr><tr><td>In air with 400 ppm of SO<sub>2</sub></td><td>1.7x10<sup>-4</sup></td></tr></tbody></table>

<figure><img src="image_37.png" /></figure>

<table><thead><tr><th>CMSX-4</th><th>k<sub>p</sub> (mg<sup>2</sup>.cm<sup>-4</sup>.s<sup>-1</sup>)</th></tr></thead><tbody><tr><td>In air</td><td>1.7x10<sup>-7</sup></td></tr><tr><td>In air with 400 ppm of SO<sub>2</sub></td><td>5.3x10<sup>-5</sup></td></tr></tbody></table>

<figure><img src="image_38.png" /></figure>

in air with 400 ppm of SO₂

<figure><img src="image_39.png" /></figure>

TROPEA: Initiation and propagation stage

CMSX-4: Initiation stage

In air with sulfur dioxide
induces much greater
corrosion than in air!
In air
TROPEA

<figure><img src="image_40.png" /></figure>

CMSX-4

<figure><img src="image_41.png" /></figure>

2 different attacked areas in TROPEA vs. only one area in CMSX-4
Zone A

<figure><img src="image_42.png" /><figcaption>CMSX-4</figcaption></figure>

<figure><img src="image_43.png" /></figure>

Porous corrosion
products
γ' depletion area

Substrate

Porous corrosion
products
γ' depletion area

Substrate
Zone A

TROPEA

<figure><img src="image_44.png" /></figure>

CMSX-4

<figure><img src="image_45.png" /></figure>

Porous corrosion
products
γ' depletion area

Porous corrosion
products
γ' depletion area

Substrate

Substrate

<table><thead><tr><th></th><th>TROPEA</th><th>CMSX-4</th></tr></thead><tbody><tr><td>Corrosion products at the surface (XRD, Spectroscopy Raman)</td><td colspan="2">NiO, γ-Al<sub>2</sub>O<sub>3</sub>, NaTaO<sub>3</sub> and Na<sub>2</sub>CrO<sub>4</sub></td></tr></tbody></table>

SAME BEHAVIOR
TROPEA

<figure><img src="image_46.png" /><figcaption>Zone A</figcaption></figure>

<figure><img src="image_47.png" /></figure>
## TROPEA

### Zone B

<figure><img src="image_48.png" /><figcaption>**Internal area**</figcaption></figure>

<figure><img src="image_49.png" /><figcaption>**Intermediate area**</figcaption></figure>

<figure><img src="image_50.png" /><figcaption>**Interface internal area/substrate**</figcaption></figure>

<figure><img src="image_51.png" /></figure>

<figure><img src="image_52.png" /></figure>

<figure><img src="image_53.png" /></figure>
CMSX-4

Zone A

<figure><img src="image_54.png" /></figure>

<figure><img src="image_55.png" /></figure>
$$ \text{In air} + 400 \text{ ppm of } \text{SO}_2 $$
TROPEA

<figure><img src="image_56.png" /></figure>

CMSX-4

<figure><img src="image_57.png" /></figure>
Zone A

TROPEA

<figure><img src="image_58.png" /></figure>

CMSX-4

<figure><img src="image_59.png" /></figure>

Porous corrosion products

Corrosion products

Substrate

Porous corrosion products

Corrosion products

Substrate

<table><thead><tr><th></th><th>TROPEA</th><th>CMSX-4</th></tr></thead><tbody><tr><td>Corrosion products at the surface (XRD, Spectroscopy Raman):</td><td>NiO</td><td>NiO and Al<sub>2</sub>O<sub>3</sub></td></tr></tbody></table>
TROPEA

Zone A

<figure><img src="image_60.png" /></figure>

Porous area

<figure><img src="image_61.png" /></figure>

Internal area

<figure><img src="image_62.png" /></figure>

Intermediate area

<figure><img src="image_63.png" /></figure>

Interface internal area/substrate

<figure><img src="image_64.png" /></figure>

<figure><img src="image_65.png" /></figure>
TROPEA
Zone B

<figure><img src="image_66.png" /></figure>

Porous corrosion products

γ' depletion area

Substrate

<figure><img src="image_67.png" /></figure>

NiO

Oxides (Cr, Al)

Cr sulfides
CMSX-4
Zone A

<figure><img src="image_68.png" /></figure>

<figure><img src="image_69.png" /><figcaption>Porous area</figcaption></figure>

<figure><img src="image_70.png" /><figcaption>Internal area</figcaption></figure>

<figure><img src="image_71.png" /><figcaption>Interface internal area/substrate</figcaption></figure>

<figure><img src="image_72.png" /></figure>
Hot corrosion degradation is more important for
TROPEA than CMSX-4 for both atmosphere
Hot corrosion degradation is more important for TROPEA than CMSX-4 for both atmosphere

<figure><img src="image_73.png" /></figure>

High proportion of eutectic phases in TROPEA
Conclusions: Different chemical composition

<table><thead><tr><th></th><th></th><th>Ni</th><th>Cr</th><th>Mo</th><th>Co</th><th>W</th><th>Re</th><th>Al</th><th>Ti</th><th>Ta</th><th>Pt</th><th>Hf</th></tr></thead><tbody><tr><td>CMSX-4</td><td>wt.%</td><td>Bal.</td><td>6.4</td><td>0.6</td><td>9.7</td><td>6.4</td><td>2.9</td><td>5.6</td><td>1.1</td><td>6.5</td><td>/</td><td>0.1</td></tr><tr><td>TROPEA</td><td>wt.%</td><td>Bal.</td><td>6.5</td><td>0.6</td><td>9.0</td><td>6.0</td><td>1.0</td><td>5.6</td><td>1.0</td><td>9.0</td><td>2.0</td><td>0.1</td></tr></tbody></table>
Conclusions: Different chemical composition

<table><thead><tr><th></th><th></th><th>Ni</th><th>Cr</th><th>Mo</th><th>Co</th><th>W</th><th>Re</th><th>Al</th><th>Ti</th><th>Ta</th><th>Pt</th><th>Hf</th></tr></thead><tbody><tr><td>CMSX-4</td><td>wt.%</td><td>Bal.</td><td>6.4</td><td>0.6</td><td>9.7</td><td>6.4</td><td>2.9</td><td>5.6</td><td>1.1</td><td>6.5</td><td>/</td><td>0.1</td></tr><tr><td>TROPEA</td><td>wt.%</td><td>Bal.</td><td>6.5</td><td>0.6</td><td>9.0</td><td>6.0</td><td>1.0</td><td>5.6</td><td>1.0</td><td>9.0</td><td>2.0</td><td>0.1</td></tr></tbody></table>

<figure><img src="image_74.png" /></figure>

Zone A

<figure><img src="image_75.png" /></figure>

NaTaO₃

Non-protective
oxide layer (Ni, Al)

Cr sulfides

γ' depletion area

Substrate

In air

<figure><img src="image_76.png" /></figure>

Zone B

NiO

Cr₂O₃

Ta₂O₅

Non-protective
oxide layer (Al, Ni)

Pt

Al₂O₃

Phases rich in Hf
and Re

Substrate

Rame et al., *Superalloys* 2020, **2020**, 71-81

Chang et al., *Corrosion science* 98, **2015**, 585-591

Chang et al. *Corrosion Science* 117, **2017**, 35-42
# Conclusions: Different chemical composition

<table><thead><tr><th></th><th></th><th>Ni</th><th>Cr</th><th>Mo</th><th>Co</th><th>W</th><th>Re</th><th>Al</th><th>Ti</th><th>Ta</th><th>Pt</th><th>Hf</th></tr></thead><tbody><tr><td>CMSX-4</td><td>wt.%</td><td>Bal.</td><td>6.4</td><td>0.6</td><td>9.7</td><td>6.4</td><td>2.9</td><td>5.6</td><td>1.1</td><td>6.5</td><td>/</td><td>0.1</td></tr><tr><td>TROPEA</td><td>wt.%</td><td>Bal.</td><td>6.5</td><td>0.6</td><td>9.0</td><td>6.0</td><td>1.0</td><td>5.6</td><td>1.0</td><td>9.0</td><td>2.0</td><td>0.1</td></tr></tbody></table>

<figure><img src="image_77.png" /></figure>

## Zone A

<figure><img src="image_78.png" /></figure>

## In air

NaTaO₃

Non-protective
oxide layer (Ni, Al)

Cr sulfides

γ' depletion area

Substrate

$$Na_2O + Ta_2O_5 \rightarrow 2NaTaO_3$$

NaTaO₃: Beneficial effect!
# Conclusions: Different chemical composition

<table><thead><tr><th></th><th></th><th>Ni</th><th>Cr</th><th>Mo</th><th>Co</th><th>W</th><th>Re</th><th>Al</th><th>Ti</th><th>Ta</th><th>Pt</th><th>Hf</th></tr></thead><tbody><tr><td>CMSX-4</td><td>wt.%</td><td>Bal.</td><td>6.4</td><td>0.6</td><td>9.7</td><td>6.4</td><td>2.9</td><td>5.6</td><td>1.1</td><td>6.5</td><td>/</td><td>0.1</td></tr><tr><td>TROPEA</td><td>wt.%</td><td>Bal.</td><td>6.5</td><td>0.6</td><td>9.0</td><td>6.0</td><td>1.0</td><td>5.6</td><td>1.0</td><td>9.0</td><td>2.0</td><td>0.1</td></tr></tbody></table>

## Zone A

<figure><img src="image_79.png" /></figure>

NaTaO₃

Non-protective
oxide layer (Ni, Al)

Cr sulfides

γ' depletion area

Substrate

## In air

$$Na_2O + Ta_2O_5 \rightarrow 2NaTaO_3$$

NaTaO₃: Beneficial effect!

Effect of Ta/Cr (wt.%) ratio:

Ta/Cr ratio > 0.5: Ta-oxides grew competitively

with Cr₂O₃ → Hot corrosion resistance

Ratio Ta/Cr of TROPEA ≈ 1.4

Rame et al., *Superalloys* 2020, **2020**, 71-81

Chang et al., *Corrosion science* 98, **2015**, 585-591

Chang et al. *Corrosion Science* 117, **2017**, 35-42
<table><thead><tr><th></th><th></th><th>Ni</th><th>Cr</th><th>Mo</th><th>Co</th><th>W</th><th>Re</th><th>Al</th><th>Ti</th><th>Ta</th><th>Pt</th><th>Hf</th></tr></thead><tbody><tr><td>CMSX-4</td><td>wt.%</td><td>Bal.</td><td>6.4</td><td>0.6</td><td>9.7</td><td>6.4</td><td>2.9</td><td>5.6</td><td>1.1</td><td>6.5</td><td>/</td><td>0.1</td></tr><tr><td>TROPEA</td><td>wt.%</td><td>Bal.</td><td>6.5</td><td>0.6</td><td>9.0</td><td>6.0</td><td>1.0</td><td>5.6</td><td>1.0</td><td>9.0</td><td>2.0</td><td>0.1</td></tr></tbody></table>

<figure><img src="image_80.png" /></figure>

In air with 400 ppm of SO₂

Zone A

<figure><img src="image_81.png" /></figure>

NiO

Non-protective
oxide layer (Al, Cr, Ta)

Cr sulfides

γ' depletion area

TaS₂

Substrate

Zone B

<figure><img src="image_82.png" /></figure>

NiO

Non-protective
oxide layer (Al, Cr)

Cr sulfides

Substrate
<table><thead><tr><th></th><th></th><th>Ni</th><th>Cr</th><th>Mo</th><th>Co</th><th>W</th><th>Re</th><th>Al</th><th>Ti</th><th>Ta</th><th>Pt</th><th>Hf</th></tr></thead><tbody><tr><td>CMSX-4</td><td>wt.%</td><td>Bal.</td><td>6.4</td><td>0.6</td><td>9.7</td><td>6.4</td><td>2.9</td><td>5.6</td><td>1.1</td><td>6.5</td><td>/</td><td>0.1</td></tr><tr><td>TROPEA</td><td>wt.%</td><td>Bal.</td><td>6.5</td><td>0.6</td><td>9.0</td><td>6.0</td><td>1.0</td><td>5.6</td><td>1.0</td><td>9.0</td><td>2.0</td><td>0.1</td></tr></tbody></table>

Zone A

NiO

Non-protective
oxide layer (Al, Cr, Ta)

Cr sulfides

γ' depletion area

TaS₂

Substrate

In air with 400 ppm of SO₂

<figure><img src="image_83.png" /></figure>

<figure><img src="image_84.png" /><figcaption>Ellingham diagram for sulfide</figcaption></figure>

Rame et al., *Superalloys* 2020, **2020**, 71-81

Chang et al., *Corrosion science* 98, **2015**, 585-591

Chang et al. *Corrosion Science* 117, **2017**, 35-42

TaS₂ block the formation of NaTaO₃?
# Conclusions: µ-structural influence + chemical composition variation

TROPEA

<figure><img src="image_85.png" /></figure>

CMSX-4

<figure><img src="image_86.png" /></figure>

<table><thead><tr><th></th><th></th><th>Ni</th><th>Cr</th><th>Mo</th><th>Co</th><th>W</th><th>Re</th><th>Al</th><th>Ti</th><th>Ta</th><th>Pt</th><th>Hf</th></tr></thead><tbody><tr><td>TROPEA</td><td></td><td>Bal.</td><td>6.5</td><td>0.6</td><td>9.0</td><td>6.0</td><td>1.0</td><td>5.6</td><td>1.0</td><td>9.0</td><td>2.0</td><td>0.1</td></tr><tr><td>Eutectic</td><td>wt.%</td><td>55.9</td><td>3.6</td><td>0.6</td><td>7.1</td><td>5.2</td><td>0.0</td><td>5.9</td><td>1.3</td><td>16.9</td><td>2.7</td><td>0.2</td></tr></tbody></table>

TROPEA

<figure><img src="image_87.png" /></figure>

Eutectic
phase
➤ Investigation of phases formed during the incubation/initiation stage by In-situ SEM

➤ Investigation of oxidation behavior in air with 400 ppm of SO₂

➤ Elaboration of Al and Al/Si coating by flash aluminizing (C.F: T. Kepa paper):

<figure><img src="image_88.png" /></figure>
THANK YOU FOR YOUR ATTENTION

Lanzarote 2025 – Lanzarote, Canary Islands, SPAIN

21 March 2025

Louis HUNAULT*, Stéphane MATHIEU**, Lionel ARANDA**, Jonathan CORMIER***, Renaud PODOR****, Fernando PEDRAZA*

Email: louis.hunault@univ-lr.fr, stephane.mathieu@univ-lorraine.fr, lionel.aranda@univ-lorraine.fr; renaud.podor@cea.fr; jonathan.cormier@ensma.fr; fernando.pedraza@univ-lr.fr

* Université de La Rochelle. LaSIE UMR 7356-CNRS. 17042 La Rochelle cedex 1. France

**Institut Jean Lamour, Campus Artem, 2 allée André Guinier 54011 Nancy. France

***Institut Pprime, 1 avenue Clément ADER 86961 Chasseneuil – Futuroscope. France

****Institut de Chimie Séparative de Marcoule ICSM, Site de Marcoule, Bâtiment 426 30207 Bagnols sur Cèze. France
CMSX-4

<figure><img src="image_89.png" /></figure>

<figure><img src="image_90.png" /></figure>

TROPEA

<figure><img src="image_91.png" /></figure>
<figure><img src="image_92.png" /><figcaption>Superposition of the thermodynamic phase stability diagram of the Ta–S–O and Cr–S–O system</figcaption></figure>
<figure><img src="image_93.png" /></figure>