Hot Corrosion Behavior of Ti45Al8.5Nb Alloy: Effect of Anodization and Pre-oxidation

doi:10.1007/s40195-022-01380-z

Abstract

Abstract:

The hot corrosion behavior of Ti45Al8.5Nb alloy was studied in the salt of Na₂SO₄ and/or NaCl at 700 °C. To improve the hot corrosion resistance, Ti45Al8.5Nb alloy was anodized in fluorine-containing solution and pre-oxidized in air. Results showed that the combination of anodization and pre-oxidation can efficiently enhance the hot corrosion resistance of Ti45Al8.5Nb alloy contaminated with Na₂SO₄ or Na₂SO₄ + NaCl deposits. This is because anodization and pre-oxidation result in the formation of compact Al₂O₃ layer which can act as a diffusion barrier to prevent sulfur, chlorine, and oxygen from attacking the alloy, therefore providing good resistance against hot corrosion. When exposed to NaCl deposit, however, no obvious improvement was achieved on the hot corrosion behavior no matter the alloy was anodized or further pre-oxidized in air.

Key words: Hot corrosion, TiAl alloy, Anodization, Pre-oxidation, Halogen effect

Hao-Jie Yan, Jun-Jie Xia, Lian-Kui Wu, Fa-He Cao. Hot Corrosion Behavior of Ti45Al8.5Nb Alloy: Effect of Anodization and Pre-oxidation[J]. Acta Metallurgica Sinica (English Letters), 2022, 35(9): 1531-1546.

Figures/Tables 22

Fig. 1 Top-surface SEM images of the anodized Ti45Al8.5Nb alloy: low-magnification image a, high-magnification image b

Fig. 2 Top-surface a-c and cross-sectional d SEM images of the PO-anodized Ti45Al8.5Nb alloy. e XRD pattern of the PO-anodized alloy. The symbols marked in b-d show where EDS analysis was carried out. The inset in d shows the optical image of the PO-anodized alloy

Table 1 EDS results of the points marked in Fig. 2

Point	Element (at.%)
Point	Al	Ti	O	Nb
1	18.88	14.42	65.51	1.18
2	21.69	9.08	68.53	0.70
3	24.00	6.84	67.94	1.22
4	45.01	47.77	-	7.22

Fig. 3 Mass change of bare (1), anodized (2), and PO-anodized (3) Ti45Al8.5Nb alloys with Na2SO4 deposit during hot corrosion at 700 °C. The optical images of the specimens after hot corrosion for 100 h are given

Fig. 4 XRD patterns of bare a, anodized b, PO-anodized c Ti45Al8.5Nb alloys with Na2SO4 deposit after hot corrosion for 100 h

Fig. 5 Top-surface SEM images of bare a-c, anodized d-f, and PO-anodized g-i Ti45Al8.5Nb alloys with Na2SO4 deposit after hot corrosion for 100 h. The symbols marked in each image show where EDS analysis was carried out

Table 2 EDS results of the points marked in Fig. 5

Point	Element (at.%)
Point	Ti	Al	O	Nb	Na	S
1	10.55	15.57	70.25	1.69	1.93	0.01
2	12.81	15.80	67.65	1.91	1.83	-
3	12.50	15.10	68.61	2.22	1.42	0.14
4	15.80	16.83	64.35	2.37	0.57	0.08
5	6.27	25.69	67.20	0.73	0.11	-
6	7.32	23.08	68.70	0.74	0.16	-

Fig. 6 Cross-sectional SEM images a, c, e and corresponding EDS elemental maps b, d, f of Ti, Al, Nb, and O for bare a, b, anodized c, d, PO-anodized e, f Ti45Al8.5Nb alloys with Na2SO4 deposit after hot corrosion for 100 h. The symbols marked in each image show where EDS analysis was carried out

Table 3 EDS results of the points marked in Fig. 6

Point	Element (at.%)
Point	Ti	Al	O	Nb	Na	S
1	20.08	38.09	6.16	1.50	0.15	34.02
2	20.70	55.30	3.03	0.75	0.02	20.20
3	34.98	7.05	6.52	0.04	-	51.41
4	17.32	58.83	4.02	1.48	0.12	18.23
5	38.63	6.88	8.99	0.05	-	45.44
6	23.32	65.76	1.69	0.21	0.04	8.99
7	29.75	16.24	7.63	0.06	-	46.30
8	41.36	5.47	7.87	0.18	-	45.11

Fig. 7 Mass change of bare (1), anodized (2), and PO-anodized (3) Ti45Al8.5Nb alloys with NaCl deposit during hot corrosion at 700 °C. The optical images of the specimens after hot corrosion for 100 h are given

Fig. 8 XRD patterns of bare a, anodized b, PO-anodized c Ti45Al8.5Nb alloys with NaCl deposit after hot corrosion for 100 h

Fig. 9 Top-surface SEM images of bare a, b, anodized c, d, PO-anodized e, f Ti45Al8.5Nb alloys with NaCl deposit after hot corrosion for 100 h. The symbols marked in each image show where EDS analysis was carried out

Table 4 EDS results of the points marked in Fig. 9

Point	Element (at.%)
Point	Ti	Al	O	Nb	Na	Cl
1	12.02	13.62	70.82	1.99	1.51	0.05
2	10.63	5.60	76.77	2.62	4.30	0.08
3	20.71	9.01	60.97	5.61	3.48	0.22
4	17.46	2.80	70.37	5.18	4.02	0.17
5	24.50	2.12	69.62	0.05	3.30	0.41
6	12.09	16.51	59.48	6.11	5.61	0.19
7	2.93	9.81	58.75	13.96	14.51	0.04
8	17.30	7.98	73.45	0.07	1.10	0.09
9	21.24	3.17	73.37	0.04	1.91	0.28
10	21.50	7.92	62.17	6.02	7.92	0.30

Fig. 10 Cross-sectional SEM images of bare a, b, anodized c, d, PO-anodized e, f Ti45Al8.5Nb alloys with NaCl deposit after hot corrosion for 100 h. The symbols marked in each image show where EDS analysis was carried out

Table 5 EDS results of the points marked in Fig. 10

Point	Element (at.%)
Point	Ti	Al	O	Nb	Na	Cl
1	52.84	5.83	29.90	9.49	0.52	1.43
2	19.94	9.28	64.33	1.70	4.59	0.16
3	47.29	40.56	5.86	6.29	-	-
4	21.24	13.00	60.96	3.05	1.63	0.12
5	40.65	22.39	48.01	4.18	0.14	0.48
6	22.97	25.18	41.44	3.21	2.17	0.03
7	44.61	41.77	7.26	6.36	-	-
8	43.90	40.18	5.53	10.39	-	-
9	35.52	19.97	38.47	4.40	0.12	1.52
10	46.75	42.88	3.86	6.51	-	-
11	46.39	39.62	3.48	10.51	-	-

Fig. 11 Mass change of bare (1), anodized (2), and PO-anodized (3) Ti45Al8.5Nb alloys with 75 wt% Na2SO4 + 25 wt% NaCl deposit during hot corrosion at 700 °C. The optical images of the specimens after hot corrosion for 100 h are given

Fig. 12 XRD patterns of bare a, anodized b, PO-anodized c Ti45Al8.5Nb alloys with 75 wt% Na2SO4 + 25 wt% NaCl after hot corrosion for 100 h

Fig. 13 Top-surface SEM images of bare a-c, anodized d-f, PO-anodized g-j Ti45Al8.5Nb alloys with 75 wt% Na2SO4 + 25 wt% NaCl after hot corrosion for 100 h. The symbol marked in the images shows where EDS analysis was carried out

Table 6 EDS results of the points marked in Fig. 13

Point	Element (at.%)
Point	Ti	Al	O	Nb	Na	Cl	S
1	2.53	0.42	62.46	17.90	16.57	0.12	-
2	27.40	7.16	61.11	4.26	-	0.07	-
3	16.48	3.11	73.12	6.46	0.51	0.06	0.26
4	9.39	15.50	59.69	8.96	6.36	0.10	-
5	16.55	1.48	78.47	3.31	0.17	0.01	-
6	23.42	6.93	62.11	7.08	0.32	0.15	-
7	10.11	17.39	67.04	4.77	0.21	0.47	-

Fig. 14 Cross-sectional SEM images a, c, e and corresponding EDS elemental maps b, d, f of Ti, Al, Nb, and O for bare a, b, anodized c, d, PO-anodized e, f Ti45Al8.5Nb alloys with 75 wt% Na2SO4 + 25 wt% NaCl after hot corrosion for 100 h. The symbols marked in each image show where EDS analysis was carried out

Table 7 EDS results of the points marked in Fig. 14

Point	Element (at.%)
Point	Ti	Al	O	Nb	Na	Cl	S
1	17.77	13.86	63.82	3.48	0.91	0.08	0.09
2	16.13	15.57	61.74	3.52	3.04	-	-
3	45.54	42.65	5.11	6.70	-	-	-
4	45.25	42.76	2.15	9.84	-	-	-
5	14.75	14.45	67.82	2.40	0.56	0.01	0.01
6	48.11	40.27	5.23	6.39	-	-	-
7	46.51	41.63	1.52	10.34	-	-	-
8	17.84	21.96	59.11	0.89	0.11	0.10	-
9	20.00	19.45	57.17	2.70	0.27	0.19	0.22
10	46.17	44.70	2.52	6.61	-	-	-

Fig. 15 Schematic illustration of hot corrosion process of bare a, anodized b, and PO-anodized c Ti45Al8.5Nb alloys

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