高温酸化アルミナ皮膜の生成・相変態におよぼす
種々の因子	
ー初期酸化皮膜から安定アルミナ皮膜への遷移ー	

林 重成	 
東京工業大学大学院理工学研究科
材料工学専攻Protection of Heat-resistant Alloys Against HighTemperature Oxidation and Corrosion	
Higher Temperature
Oxidizing, Corrosive atmospheres
Oxide Scale

1. Compact, Higher thermo-dynamical Stability
2. Good adhesion to substrate
3. Rapid formation, maintained for longer time

Cr2O3, Al2O3, and SiO2
Alloy

SiO2
Al2O3

Cr2O3800	
Steam turbines
Boiler tubes
Chemical plants

1000	

Gas turbines
Jet engines

1200℃	
Rocket engines

Growth of Metastable and α-Al2O3 Scale
Ni-22Al-30Pt-Hf in air at 1150oC
0.80.7Weight change, mg/cm2

0.60.5α-Al2O30.40.30.2

metastable Al2O30.100200

400600

Number of 1h cycles

8001000

Typical Forms Thermally Grown Alumina

α-Al2O3(Corundum)	

γ-Al2O3(Cubic)	

Alloy composition	
θ-Al2O3(Monoclinic)	

Atmosphere	Temperature	TTT Diagram of Thermally Grown Alumina

alloy with Al deposition

FeCrAl alloy

S. Taniguchi and A. Andoh, Oxid. Met., 58, (2002), 545.

Growth rates of metastable and α-Al2O3 scales
10-­‐10	  temperature	  (ºC)	  1400	   1200	  1000	   900	  kp (g2/cm4s)

10-­‐11	  800	  700	  θ-­‐Al2O3	  on	  NiAl	  10-­‐12	  α-­‐Al2O3	  on	  NiAl	  10-­‐13	  10-­‐14	  θ-­‐Al2O3	  on	  FeAl	  α-­‐Al2O3	  on	  FeAl	  γ-­‐Al2O3	  on	  NiAl	  10-­‐15	  10-­‐16	  9	  8	  6	  7	  reciprocal	  temperature	  (104/K)	  10	  Effect(s) of Fe Deposit on the Phase Transformation
to α-Al2O3
Fe deposit	
β-NiAl substrate	
Fe deposited area

900oC for 10h in air	α-­‐Al2O3	  metastable-­‐Al2O3	  T. Nishimoto, T. Narita, JIM annual meeting, (2007).

Metal Coating Dependence on Metastable Al2O3
Formation
1Fe-50Al

0.8

at 900ºC~50nm

Ni coating
Fe50Al0.60.4

Cr coating
No-metastable
Al2O3 formation	

0.2
00100

200

metastable Al2O3	

mass gain (mg/cm2)

Metal deposit

Fe coating

300 400
Time (h)500

600

Y. Kitajima, S. Hayashi, et al., Oxid. Met., (2010)	

Metal Coating Dependence on Metastable Al2O3
Ni coating
Formation
1Fe-Al	mass gain (mg/cm2)

Metal Coating

Fe-50Al0.8

at 900ºC~50nm

Ni coating

Fe-Al	

Fe50Alnon coating
0.6

Cr coating

0.4
Cr coating

Fe-Al	0.2Fe coating

0α-Al O
20100Fe coating

3	200Fe-Al	300 400
Time (h)500600Y. Kitajima, S. Hayashi, et al., Oxid. Met., (2010)	

Purpose of the Study

Clarify the effect of various elements on thetransformation behavior of Al2O3 scale during HToxidation by in-situ HT X-ray diffraction study bymeans of synchrotron radiation.

Experimental Setup for In-situ Measurement	

X-ray beam
Energy:12.4 keV, λ=1ÅPILATUS2D detector	

Heating rate: 10-100°C/min

Storage ring	
X-ray beam	~12.5°	

Heating stage	Sample	
Thermocouple	Experimental Setup for In-situ Measurement	

Furnace	
8-axis stage	
2D detector 	Stage	

X-ray beam	

2D detector 	
Furnace	Experimental Procedures	
Effect of Fe on the Transformation of Al2O3 Scale

Alloys: Fe-45~52at%Al (FeAl)
Coatings: Fe ~100nm (PVD)
Oxidation: in air, air + 7.6H2O
in lowPO2 = 1.8 x 10-13 atm (Ar-0.9H2-7.6H2O)(FeO/Fe3O4, 1.2 x 10-12 atm)
at 1000 ~ 1100°C
Heating and cooling rate : 50°C/min for heating
about 300°C/min for cooling
Oxidation time: 1 or 4h 	Evolution of Oxide Scale during the HT Oxidation	
Non-coated Fe-Al at 1000°C for 4h	589°C	

Cooling	

32°C	

999°C	999°C	
(113)	 999°C	
(006)	
999°C	

(104)	
α-Al2O3999°C	
999°C	

(401)	 (002)	

997°C	

867°C	
θ-Al2O3379°C	

High-angle 	

Heating	

948°C	

Isothermal oxidation for 4h	

999°C	

Change in Intensities of Different Al2O3 Phases 	
20

1000

Temperature
α-Al2O3(104)	

Intensity, a.u.	

600
10Heating	

400

α-Al2O3(113)	

5

θ-Al2O3(002)	
01015

20

25

Oxidation time, min	

200

30350Temperature, °C	

15800

Change in Lattice Spacing of α-Al2O3	
α-Al2O3 (104)	

2.59

Temperature1000

2.58800

2.575

600

d=2.5724: Pure-Al2O3 at 1000°C	

2.57

400

2.565

200

2.56

0050

100

150

Oxidation time, min	200

Temperature, °C	

Lattice spacing, Å	2.585

1200

Evolution of Oxide Scale During the HT Oxidation	
462°C	
998°C	
(113)	
998°C	

(104)	

999°C	
(110)	

998°C	
999°C	

α-Al2O3

998°C	
947°C	

Cooling	 Isothermal oxidation for 1h	

101°C	

866°C	
(113)	

703°C	
541°C	

Fe2O3

378°C	
297°C	

High-angle 	

Heating	(104)	
(110)	

Fe-coated Fe-Al at 1000°C for 1h	Change in Lattice Spacing of Oxide Scale	800°C	
2.72

Temperature2	2.71

1000800Fe2O3 (104)	

2.7

Fe2O3 at 1000°C	400200

2.69 d=2.7032: Al2O3-saturated
2.59600

3	1	α-Al2O3 (104)	

Fe2O3	d=2.5795: Fe2O3-saturated
Al2O3 at 1000°C	

Fe2O3	Al2O3	2.565

3	020

4060

Oxidation time, min	

Fe-Al	Saturation of Al2O3in Fe2O3	

2.57 d=2.5719: Pure-Al2O3 at 1000°C	

2.56

Fe-Al	

Therm. Exp. of Fe2O3	

2	2.58
2.575

Fe2O3	0Oxidation time, min	

2.585

Temperature, °C	

1	Lattice spacing, Å	1200

d=2.7214: Pure-Fe2O3 at 800°C	80100Fe-Al	Precipitation of Al2O3	

TEM Cross-section and EDS Analysis of α-Al2O3
Fe-coated Fe-Al at 1000°C for 1h	1	2	3	6	4	7	5	8	9	11	12	10	Fe-Al	Fe	(in at.%)	
Al	O	
Solid Solution	

1	42.0	

7.1	

2	

2.5	

29.1	 68.3	 7.9 mol%Fe2O3	

3	1.4	

31.3	 67.3	 4.3 mol%Fe2O3	

4	0.1	

30.6	 69.3	 0.3 mol%Fe2O3	

5	0.2	

31.3	 68.5	 0.6 mol%Fe2O3	

6	

2.5	

30.7	 66.8	 7.5 mol%Fe2O3	

7	1.9	

28.1	 70.1	 6.3 mol%Fe2O3	

8	0.3	

32.6	 67.1	 0.9 mol%Fe2O3	

9	0.0	

31.5	 58.5	10	0.2	32.9	 67.0	 0.6 mol%Fe2O3	

50.9	 14.5 mol%Al2O3	0 mol%Fe2O3	

11	 35.1	

6.5	

12	33.9	 64.9	 3.4 mol%Fe2O3	

1.2	

58.4	 15.6 mol%Al2O3	Effect of PO2 on the Transformation of Al2O3	
Bulk Fe-52Al oxidized in air, air+H2O or H2/H2O at 1100°C	(a)	θ-Al2O3(002)	

α-Al2O3(104)	

air	 Isothermal
FeAl2	

oxidation	

Intensity, a.u.	

heating	(b)	

Air+H2O	 Isothermaloxidation	
heating	(c)	H2/H2O Isothermal(low PO2)	 oxidation	
heating	Two theta, degree	Effect of H2O and/or PO2 on the Transformation to α-Al2O3	
θ-Al2O3	403020Fe-50at%Al合金
1100℃air	Intensity, a.u.	

10α-Al2O3	01412108642040

θ-Al2O3	H2/H2O	
α-Al2O3	
θ-Al2O3	30Air+H2O	

2010α-Al2O3	00204060Oxidation time, min	80100

TEM Cross-sections of α-Al2O3
Bulk Fe-52Al at 1100°C for 1h (40min)	
in air for 1h 	in air+H2O for 40min	

α-Al2O3	

α-Al2O3	400nm	
in H2/H2O for 1h	400nm	

400nm	

Effect of PO2 on the Transformation of Al2O3	Fe-coated Fe-52Al oxidized in air or H2/H2O at 1100°C	
α-Al2O3	Fe2O3	 α-Al2O3	
Fe2O3	

Fe2O3	air	Intensity, a.u.	

Isothermaloxidation	
FeAl2	

FeAl2	
heating	

FeAl2O4	
θ-Al2O3	

FeAl2O4	
α-Al2O3	
θ-Al2O3	
α-Al2O3	

Fe3O4	FeO	2θ, degree	

H2/H2O	
Isothermaloxidation	
heating	TEM Cross-sections of α-Al2O3
Fe-coated Fe-52Al at 1100°C for 1h (40min)	

in air for 1h 	in H2-H2O for 1h	Fe2O3	

α-Al2O3	

FeAl2O4	

FeAl	
FeFeAl2O	 3 is necessary to form α-Al2O
3 without metastable
Al2O3 formation 	
400nm	

α-Al2O3	400nm	

Modified Ternary Fe-Al-O System0air

Fe2O3

α-Al2O3-8Fe3O4

H2/H2OFeAl2O4

α-Al2O3+FeAl2O4

FeAl2O4+FeO
γ-Fe+FeAl2O4log Po2 (atm)-16γ-Fe+Al2O3-24

θ-Al2O3-32

α-Fe+Al2O3α-Fe

γ-Fe-40
0Fe2O320ξ η4060
Mol %Lθ80

100
Al2O3F.A. Elrefair and W.W. Smeltzer, Met. Trans. B, (1983)	

SummaryFormation of α-A 2 O 3 from Fe 2 O 3 was confirmed by in-situ
measurement via synchrotron radiation.
Precipitation of α-Al2O3 (sympathetic nucleation) occurred whenFe-coated alloy was oxidized in air.
In low PO2, Metastable Al2O3 formed and it’s transformation to αAl2O3 delayed.
Transformation to α-A2O3 was delayed and/or metastable θ-Al2O3 wasstabilized:- On the alloys with lower Fe content.
- In the atmosphere with lower partial pressure of oxygen.
Lower Fe content in the metastable Al2O3 delayed thetransformation.