Oxidation Performance and Interdiffusion Behaviour of two MCrAlY Coatings on a Fourth-Generation Single-Crystal Superalloy

doi:10.1007/s40195-021-01287-1

Abstract

Abstract:

The oxidation behaviour of a fourth-generation single-crystal superalloy without coating and with two types of MCrAlY coatings at 1140 °C was studied. The results showed that both coatings greatly improved the oxidation resistance of the superalloy, and the addition of Hf further improved the oxidation resistance by pinning the oxide layer into the coating. Before and after oxidation, obvious Cr and Al interdiffusion was detected. Inward Cr diffusion induces the precipitation of a topologically close-packed phase, while the diffusion of Al affects the structure of the γ/γ' phase, the solubility of refractory elements, and the formation of an interdiffusion zone.

Key words: Superalloys, Metal coatings, Oxidation, Electron probe microanalyser (EPMA), Element diffusion

K. J. Tan, J. J. Liang, X. G. Wang, X. P. Tao, J. Gong, C. Sun, Y. Z. Zhou, X. F. Sun. Oxidation Performance and Interdiffusion Behaviour of two MCrAlY Coatings on a Fourth-Generation Single-Crystal Superalloy[J]. Acta Metallurgica Sinica (English Letters), 2022, 35(4): 679-692.

Figures/Tables 17

Table 1 Chemical composition of the superalloy (wt%)

W + Mo + Ta	Co	Cr	Al	Re	Ru	Ni
15	12	4	5.8	6	3	Bla.

Table 2 Chemical composition of the targets of two coatings (wt%)

Coating	Co	Cr	Al	Si	Y	Hf	Ni
A	32	20	10	0.1	0.6	-	Bla.
B	20	28	10	0.1	0.6	0.1	Bla.

Fig. 1 Microstructure of as-cast a and heat-treated b superalloys

Fig. 2 Microstructure of surface and cross section of samples with coating A a, b and coating B c, d before oxidation

Table 3 Element composition in different regions of the two samples (wt%)

Elements	Sample A			Sample B
Elements	Substrate	IDZ	Coating	Substrate	IDZ	Coating
Al	5.4	6.8	7.4	5.8	5.9	6.3
Cr	4.6	8.5	20.8	4.1	10.8	26.5
Co	11.9	18.4	32.1	12.2	10.2	22.6
Ni	52.1	51.4	39.7	54.6	49.2	44.3
Ru	3.6	0.8	-	2.9	2.0	-
Ta	7.6	7.3	-	8.9	9.8	-
W	10.2	4.4	-	5.4	6.3	-
Re	4.5	2.4	-	6.2	5.9	-
Hf	-	-	-	-	-	0.4

Fig. 3 Element distribution of sample A before oxidation

Fig. 4 Element distribution of sample B before oxidation

Fig. 5 Mass change of the substrate sample and two types of coatings samples during isothermal oxidation at 1140 °C

Fig. 6 XRD patterns of coating A a and coating B b samples before and after oxidation at different times

Fig. 7 Microstructure of surface with substrate a, d samples after 10 h exposure as well as sample A b, e and sample B c, f samples after 100 h exposure

Fig. 8 Microstructure of cross section of sample A in surface region a, near surface region b, coating c, and IDZ d

Fig. 9 Microstructure of cross section of sample B in surface region a, IDZb, interior region c, d, and full view e

Table 4 Thickness of each area of two coating samples after oxidation (μm)

Oxidation Time (h)	Coating A			Coating B
Oxidation Time (h)	IDZ	SRZ	Al₂O₃	IDZ	SRZ	Al₂O₃
0	0	0	0	12	0	0
10	17	14	2.1	20	17	3.1
100	54	19	2.5	51	Full	5.3
200	89	0	2.8	92	Full	5.8

Fig. 10 Composition change curve of elements at different positions from the surface of two samples before a, b and after oxidation for 100 h c, d

Fig. 11 Morphology and element composition of the TCP phase in SRZ of sample B

Fig. 12 Element distribution of sample A after oxidation for 100 h

Fig. 13 Element distribution of sample B after oxidation for 100 h

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