Influences of Iridium and Palladium on Oxidation Resistance of PtAl Coating

doi:10.1007/s40195-020-01185-y

Abstract

Abstract:

The overarching goal of present study is to investigate the effects of Ir and Pd additions on the oxidation behaviour of PtAl coatings. Prior to depositing standard PtAl coating, Ir layer was electroplated by IrBr₃ aqueous solution while Pd layer was prepared using electroless deposition. Comparing with normal PtAl coating, cyclic oxidation tests were carried out on both the Ir- and Pd-modified aluminide coatings. The results showed that Ir-modified PtAl coating exhibited better oxidation resistance than both Pd-modified and normal PtAl coatings because Ir partly served as diffusion barrier to reserve Al while Pd did not.

Key words: Thermal barrier coating, PtAl coating, Oxidation resistance, Iridium, Palladium

Ling-Yi Qian, Jing Wang, Yun-Shan Guo, He Liu, Ze-Bin Bao. Influences of Iridium and Palladium on Oxidation Resistance of PtAl Coating[J]. Acta Metallurgica Sinica (English Letters), 2021, 34(8): 1120-1130.

Figures/Tables 17

Fig. 1 Schematic diagram of the thermal cycling test rig: a furnace photo, b cooling stage set-up, c heating stage set-up

Fig. 2 BSE images of Pd coatings on M246 with different deposition time: a 30 min, b 45 min, c 60 min

Fig. 3 Surface morphologies of as-deposited Pd coatings after various deposition time: a 45 min, b 60 min. The labelled locations indicate the clusters and cracks after deposition

Table 1 EDS result of electroless plated Pd coating

Element	Content (wt%)
Pd	96
P	4

Fig. 4 BSE image of the microstructure of layered Pd and Pt coatings. Pt pegs can be found in the cracks of electroless deposited Pd

Fig. 5 Cross-sectional and surface morphologies of a, c as-deposited Ir coating, b, d Ir-Pt dual-layer coating

Fig. 6 Microstructures of Ir-Pt and Pd-Pt coatings on M246 after vacuum diffusion heat treatment at 1100 °C: a Ir-Pt coating after 4 h, b Pd-Pt coating after 1 h

Table 2 EDS results (wt.%) of marked area shown in Fig. 6

Marked areas	Ni	Al	Ir	Pt	Pd	Cr	Co	W
1	32.3	2.1	31.0	10.7	-	11.5	7.1	3.8
2	45.4	4.7	13.6	15.8	-	4.0	5.5	9.3
3	43.2	2.4	-	18.8	4.0	11.1	10.8	9.4
4	42.7	6.6	-	25.2	14.4	2.2	3.9	3.7
5	48.5	2.5	-	11.1	3.7	10.0	11.2	13.0

Fig. 7 Cross-sectional morphologies of the modified PtAl coatings: a Ir-PtAl-1 h coating, b Ir-PtAl-4 h coating, c Pd-PtAl coating

Table 3 EDS results (wt.%) of marked areas shown in Fig. 7

Marked areas	Ni	Al	Ir	Pt	Pd	Cr	Co	W	P
1	38.0	13.5	22.5	16.1	-	4.5	3.8	-	-
2	50.1	8.7	12.6	13.5	-	3.9	5.4	3.4	-
3	51.0	24.5	-	16.5	-	2.6	4.6	-	-
4	32.8	18.2	39.6	-	-	2.4	5.3	-	-
5	45.8	17.6		14.5	13.2	3.4	5.0	-	-
P precipitate	18.2	2.1	-	-	2.0	14.5	12.8	13.6	16.2

Fig. 8 Cross-sectional morphologies and the corresponding Al mapping profiles of the Ir-PtAl coatings: a, b Ir-PtAl-1 h coating, c, d Ir-PtAl-4 h coating

Fig. 9 TGO thickness changes of Ir-PtAl-4 h, Pd-PtAl and general PtAl coatings on M246 substrate during the thermal cyclic oxidation test

Fig. 10 Surface roughness values of Ir-PtAl-4 h, Pd-PtAl and normal PtAl coatings on M246 substrate before and after cyclic thermal oxidation

Fig. 11 Cross-sectional morphologies of Ir-PtAl-1 h coating on M246 substrate after cyclic oxidation at 1100 °C for different cycles: a 50 cycles, b 100 cycles

Table 4 EDS results (wt.%) of labelled areas in Fig. 11

Labelled area	Ni	Al	Ir	Pt	Cr	Co	Ti	W	Mo	O
1	51.2	5.2	10.7	6.0	6.7	7.0	1.5	8.5	2.2	-
2	54.7	3.3	6.8	6.6	7.7	8.3	0.9	10.5	-	-
3	21.5	21.8	-	-	7.0	4.5	0.4	-	-	42.6

Fig. 12 Microstructure evolution of Ir-PtAl-4 h a, c and e and Pd-PtAl b, d and f coatings during the cyclic thermal oxidation test: a, b 50 cycles, c, d 100 cycles, e, f 200 cycles

Table 5 EDS results (wt.%) of detected β and γ' phases in Ir-PtAl-4 h and Pd-PtAl coatings after thermal cyclic oxidation test

Phases	Ni	Al	Ir	Pt	Pd	Cr	Co	W
β 50 cycles (Ir-PtAl-4 h)	40.6	12.5	21.5	15.4	-	4.2	4.1	-
β 100 cycles (Ir-PtAl-4 h)	44.5	13.8	16.4	15.1	-	4.4	4.4	-
β 200 cycles (Ir-PtAl-4 h)	41.0	13.8	14.5	14.9	-	4.4	3.7	-
β 50 cycles (Pd-PtAl)	48.7	15.0	-	13.0	14.0	4.0	4.6	-
β 100 cycles (Pd-PtAl)	47.4	14.8	-	14.2	14.4	3.8	4.7	-
β 200 cycles (Pd-PtAl)	47.0	14.7	-	13.5	16.3	3.8	4.0	-
γ' 50 cycles (Pd-PtAl)	59.2	9.7		9.2	5.3	3.8	6.9	4.2
γ' 100 cycles (Pd-PtAl)	59.9	8.9	-	9.9	4.1	4.0	6.7	4.5
γ' 200 cycles (Pd-PtAl)	61.1	8.9	-	8.7	4.8	4.0	6.5	4.4
γ' 100 cycles (Ir-PtAl-4 h)	59.3	8.8	-	2.7		4.4	6.8	5.9
γ' 200 cycles (Ir-PtAl-4 h)	51.2	7.2	11.9	13.5		6.6	6.5	-

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