Formation Mechanism of Nanoparticles in Fe-Cr-Al ODS Alloy Fabricated by Direct Oxidation Method

doi:10.1007/s40195-020-01184-z

Abstract

Abstract:

This study presents the fabrication of 14Cr Fe-Cr-Al oxide dispersion strengthened (ODS) alloy by a direct oxidation process. In order to explain how oxide nanoparticles are formed in the consolidation process, the powders after oxidation are subjected to vacuum thermal treatment at high temperatures. Differential scanning calorimeter, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy techniques are used to detect the generation, evolution of oxides on both the surface and interior of the powder, as well as the type of oxide nanoparticles in the fabricated ODS alloy. It is found that an iron oxide layer is formed on the surface of the powder during low temperature oxidation. And the iron oxide layer would be decomposed after thermal treatment at high temperature. In the consolidation process, the oxygen required by the reaction of alumina and yttrium oxide to produce nanoscale Y-Al-O particles mainly derives from the decomposition of iron oxide layer at elevated temperature and the inward diffusion of oxygen. Using the direct oxidation process, YAlO₃ nanoparticles are dispersed in the grains and at the grain boundaries of Fe-Cr-Al ODS alloy.

Key words: Fe-Cr-Al ODS alloy, Direct oxidation, Iron oxide layer, Y-Al-O nanoparticles, Formation mechanism

Fuzhao Yan, Jing Li, Yiyi Li, Liangyin Xiong, Shi Liu. Formation Mechanism of Nanoparticles in Fe-Cr-Al ODS Alloy Fabricated by Direct Oxidation Method[J]. Acta Metallurgica Sinica (English Letters), 2021, 34(7): 963-972.

Figures/Tables 16

Table 1 Chemical composition of the atomized powder (wt%)

Powder	Fe	Cr	Al	Y	Ti
Fe-Cr-Al	Bal.	13.95	4.16	0.47	0.55

Fig. 1 SEM images of dispersoids on the surface of powder 14Cr-A under alow, b high magnifications

Table 2 Composition of the surface of powder 14Cr-A (wt%)

Point	Fe	Cr	Al	Y	Ti	O
1	71.7	15.0	6.2	2.0	1.3	3.8
2	79.90	14.11	4.22	0.1	0	1.67
3	75.52	14.94	4.33	1.10	1.01	3.1
4	74.7	14.71	5.69	0.01	0.67	4.22

Fig. 2 Auger electron spectroscopy (AES) depth profile of surface chemical composition of the powder 14Cr-A

Fig. 3 DSC curve of the oxidized powder 14Cr-A

Fig. 4 SEM images of dispersoids on the surface of powder 14Cr-B under a low, b high magnifications

Table 3 Composition of the surface of powder 14Cr-B (wt%)

Point	Fe	Cr	Al	Y	Ti	O
1	75.0	11.1	7.9	2.3	0.5	3.2
2	76.2	13.2	5.7	0	0.8	4.1
3	78.9	13.3	5.8	0.1	0.2	1.7
4	78.8	11.7	6.8	0	0.5	2.2

Fig. 5 AES depth profile of surface chemical composition of powder 14Cr-B

Fig. 6 SEM images of dispersoids on the surface of powder 14Cr-C under a low, b high magnifications

Table 4 Composition of the surface of powder 14Cr-C (wt%)

Point	Fe	Cr	Al	Y	Ti	O
1	43.2	10.5	21.1	0.6	0.2	24.4
2	54.7	11.9	17.4	0	0.4	15.6
3	53.5	11.4	16.8	1.4	0.3	16.6
4	55.4	12.6	15.7	0.1	0.3	15.9

Fig. 7 AES depth profile of surface chemical composition of powder 14Cr-C

Fig. 8 TEM/HRTEM results of the as-HIPed alloy: a bright field image of nanoparticles, b particle size distribution of nanoparticles, c EDS energy spectrum and composition of particle 1 in a, d FFT pattern of particle 2 in a

Fig. 9 TEM bright field image of oxide particles near grain boundary

Table 5 Inter-planar spacing (d) and angles (α) of particle 2 and the possible indexing

d (Å), α (°)	d₁ (011)	d₂ (121)	d₃ (110)	α₁₂	α₂₃
Measured	5.357	4.469	7.135	35.48	54.58
YAlO₃	5.329	4.318	7.137	35.86	54.14

Fig. 10 Detailed XPS spectra of oxygen, iron, chromium, aluminum and yttrium near the surfaces of a 14Cr-A, b 14Cr-B, c 14Cr-C

Fig. 11 Schematic diagram for the formation process of oxide nanoparticles: a after direct oxidation, b during heating, cafter HIPing. For illustrative purposes, a small amount of chromium oxide on the surface is ignored

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