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Surface analysis of SUS 316 by SIMS, SEM and ESCA
Journal of Nuclear Materials 80 (1979) 361-363 0 North-Holland Publishing Company
LETTER TO THE EDITORS - LETTRE AUX REDACTEURS SURFACE ANALYSIS OF SUS 3 16 BY SIMS, SEM AND ESCA
tions and analyzed by the same device. One of the main reasons is considered to be as follows: the surface composition of high-temperature alloys being different from that of the bulk, depends upon the sample treatment, and the difference in surface composition may lead to different results in oxidation behaviour. So, it is essential to characterize the surface layer before as well as after oxidation. In this letter, we report the results of surface analysis of SUS 3 16 with composition vs. depth profiles analyzed by SIMS, SEM with energy-dispersive X-ray analysis (EDXA), and ESCA. The combined use of these instruments gives semi-quantitative information about not only planar but also in-depth profiles of alloy components. The details and applications of
Surface oxidation of high-temperature materials in environments of low-oxygen potential has recently become a very important problem in relation to the development of HTR. Though this problem has been investigated by many workers by various methods [l-8], some inconsistency seems to remain among the results appearing in reports. Some authors have indicated that the outermost surface of slightly oxidized stainless steel is chromium-enriched [l-5], while other authors have shown an iron-rich surface [6-81. The controversy may be partly due to the dif. ference in the thickness of the surface layer analyzed by different methods. However, the surface oxide is often found to be different from sample to sample even if the sample was oxidized under similar condi-
SUS
316
as
recieved
b)
a) 6
10
20
30
I
I
40
50
60
70
m/e
Fig. 1. Positive SIMS spectra from the sample surface of SUS 316 (a) as received, and (bj after slight sputter-etching. 361
T. Tanabe, S. Imoto /Surface
362
these modes of analysis have already been published by many workers (e.g., [lo]). The SUS 316 sample was obtained from the Japan Stainless Steel Association in the form of cold-rolled sheets. In fig. 1 are shown SIMS spectra of positive secondary ions from the sample surface, as received. Alkali metal elements such as Na, K and Mg are nearly always found in the spectra, probably because of their high sputtering yield and contamination by human hand and other sources. These elements are considered to be deposited as salt with halogen ions such as Cl, and F, which are also detected in negative SIMS spectra (not represented here). These alkali and halogen ions are, however, easily sputtered off by the argon-ion etching (see fig. 1). The ions of Cr, Fe, Si and Cu which have appeared in positive SIMS spectra are all constituent elements of SUS 316. It is noticeable, however, that only a very weak peak of Ni ions is plotted in SIMS in spite of about ten percent dissolution in the bulk. The Ni peak is found in ESCA analysis also to be weak in contrast with an appreciable height of peak (Kol X-ray) in EDXA. Fig. 2 shows the composition vs. depth profiles of Fe, Cr and Ni which were obtained by combination of SIMS analysis and Ar-ion etching, where the sputtering rate is roughly estimated to be about 2.5 A/
analysis of SUS 316
? ‘$5.0 -
Fe
> 0I_ 0 2
Cr
---...___..___
=1.0-
Li $ tz 0.5-
---...__
Fe
;
ION
ETCHING
TIME
( minutes
mechanically
min, assuming the sputtering yield is unity and independent of ion species. The figure definitely indicates surface depletion of chromium with enrichment below the surface. The almost complete disappearance of Ni in the outermost surface layer is also
polished Si C,Ca,
Ar
K .Naf
Na
MO
,
I
10
I
20
I
30
40
50
I
Fig. 2. Composition vs. depth profile of SUS 316 as received; etching rate is about 2.5 A/min (sse text).
316
SUS
----... Cr/
60
I
1
I
70
80
90
100
pig. 3. Positive SIMS spectra of mechanically polished SUS 316.
110
m/e
T. Tanabe, S. Imoto /Surface analysisof SUS 316
shown in the profile. Because of the greater penetration range of electrons and the greater escape depth of X-rays, compared with ions, such a fine depth profile with such remarkable depletion of Ni at surface was never obtained by the use of EDXA only. Fig. 3 shows the positive SIMS spectra from the sample as mechanically polished. In this case, the iron-enriched layer characteristic to the specimen as received has been polished off and a rather high concentration of chromium is identified. From surface analysis of samples oxidized at various temperatures in air, it is found that the surface composition is hardly changed by oxidation below 600°C, whereas above 600°C it is changed in various ways according to the oxidation temperature and time, owing to different diffusion behaviour of the various constituent elements. Details of the surface
Received 27 January 1979
363
analysis of oxidized samples will be published in a separate paper [ 111. References f l] T. Hirano,M. Okada, H. Yoshida and R. Watanabe, J. Nucl. Mat. 75 (1978) 304. [2] A.F. Smith and R. Hales, Werkstoff und Korrosion 28 (1977) 405. 131 R.K. Wild, Corrosion Sci. 17 (1977) 87. [4] R.L. Park et al., J. Vat. Sci. Technol. 9 (1972) 103. [S] S. Strop and R. Helm, Surface Sci. 68 (1977) 10. [6] I. Olefjord, Met. Sci. J. 9 (1975) 263. [7] R. Shubert, J. Vat. Sci. Technol. 12 (1975) 505. [8] G. Betz et al., J. Appl. Phys. 45 (1974) 5312. [9] P.F. Kane and G.B. Larrabee, Characterization of Solid Surfaces (Plenum Press, New York, 1974). [lo] R. Vanselow and S.Y. Tong, Chemistry and Physics of Solid Surfaces (CRC press, 1977). [ 1 l] T. Tanabe and S. Imoto, to be published.
Tetsuo Tanabe and Shizsuke Imoto Department of Nuclear Engineering, Faculty of Engineering, Osaka University, Yamadakami, Suita, Osaka,Japan
LETTER TO THE EDITORS - LETTRE AUX REDACTEURS SURFACE ANALYSIS OF SUS 3 16 BY SIMS, SEM AND ESCA
tions and analyzed by the same device. One of the main reasons is considered to be as follows: the surface composition of high-temperature alloys being different from that of the bulk, depends upon the sample treatment, and the difference in surface composition may lead to different results in oxidation behaviour. So, it is essential to characterize the surface layer before as well as after oxidation. In this letter, we report the results of surface analysis of SUS 3 16 with composition vs. depth profiles analyzed by SIMS, SEM with energy-dispersive X-ray analysis (EDXA), and ESCA. The combined use of these instruments gives semi-quantitative information about not only planar but also in-depth profiles of alloy components. The details and applications of
Surface oxidation of high-temperature materials in environments of low-oxygen potential has recently become a very important problem in relation to the development of HTR. Though this problem has been investigated by many workers by various methods [l-8], some inconsistency seems to remain among the results appearing in reports. Some authors have indicated that the outermost surface of slightly oxidized stainless steel is chromium-enriched [l-5], while other authors have shown an iron-rich surface [6-81. The controversy may be partly due to the dif. ference in the thickness of the surface layer analyzed by different methods. However, the surface oxide is often found to be different from sample to sample even if the sample was oxidized under similar condi-
SUS
316
as
recieved
b)
a) 6
10
20
30
I
I
40
50
60
70
m/e
Fig. 1. Positive SIMS spectra from the sample surface of SUS 316 (a) as received, and (bj after slight sputter-etching. 361
T. Tanabe, S. Imoto /Surface
362
these modes of analysis have already been published by many workers (e.g., [lo]). The SUS 316 sample was obtained from the Japan Stainless Steel Association in the form of cold-rolled sheets. In fig. 1 are shown SIMS spectra of positive secondary ions from the sample surface, as received. Alkali metal elements such as Na, K and Mg are nearly always found in the spectra, probably because of their high sputtering yield and contamination by human hand and other sources. These elements are considered to be deposited as salt with halogen ions such as Cl, and F, which are also detected in negative SIMS spectra (not represented here). These alkali and halogen ions are, however, easily sputtered off by the argon-ion etching (see fig. 1). The ions of Cr, Fe, Si and Cu which have appeared in positive SIMS spectra are all constituent elements of SUS 316. It is noticeable, however, that only a very weak peak of Ni ions is plotted in SIMS in spite of about ten percent dissolution in the bulk. The Ni peak is found in ESCA analysis also to be weak in contrast with an appreciable height of peak (Kol X-ray) in EDXA. Fig. 2 shows the composition vs. depth profiles of Fe, Cr and Ni which were obtained by combination of SIMS analysis and Ar-ion etching, where the sputtering rate is roughly estimated to be about 2.5 A/
analysis of SUS 316
? ‘$5.0 -
Fe
> 0I_ 0 2
Cr
---...___..___
=1.0-
Li $ tz 0.5-
---...__
Fe
;
ION
ETCHING
TIME
( minutes
mechanically
min, assuming the sputtering yield is unity and independent of ion species. The figure definitely indicates surface depletion of chromium with enrichment below the surface. The almost complete disappearance of Ni in the outermost surface layer is also
polished Si C,Ca,
Ar
K .Naf
Na
MO
,
I
10
I
20
I
30
40
50
I
Fig. 2. Composition vs. depth profile of SUS 316 as received; etching rate is about 2.5 A/min (sse text).
316
SUS
----... Cr/
60
I
1
I
70
80
90
100
pig. 3. Positive SIMS spectra of mechanically polished SUS 316.
110
m/e
T. Tanabe, S. Imoto /Surface analysisof SUS 316
shown in the profile. Because of the greater penetration range of electrons and the greater escape depth of X-rays, compared with ions, such a fine depth profile with such remarkable depletion of Ni at surface was never obtained by the use of EDXA only. Fig. 3 shows the positive SIMS spectra from the sample as mechanically polished. In this case, the iron-enriched layer characteristic to the specimen as received has been polished off and a rather high concentration of chromium is identified. From surface analysis of samples oxidized at various temperatures in air, it is found that the surface composition is hardly changed by oxidation below 600°C, whereas above 600°C it is changed in various ways according to the oxidation temperature and time, owing to different diffusion behaviour of the various constituent elements. Details of the surface
Received 27 January 1979
363
analysis of oxidized samples will be published in a separate paper [ 111. References f l] T. Hirano,M. Okada, H. Yoshida and R. Watanabe, J. Nucl. Mat. 75 (1978) 304. [2] A.F. Smith and R. Hales, Werkstoff und Korrosion 28 (1977) 405. 131 R.K. Wild, Corrosion Sci. 17 (1977) 87. [4] R.L. Park et al., J. Vat. Sci. Technol. 9 (1972) 103. [S] S. Strop and R. Helm, Surface Sci. 68 (1977) 10. [6] I. Olefjord, Met. Sci. J. 9 (1975) 263. [7] R. Shubert, J. Vat. Sci. Technol. 12 (1975) 505. [8] G. Betz et al., J. Appl. Phys. 45 (1974) 5312. [9] P.F. Kane and G.B. Larrabee, Characterization of Solid Surfaces (Plenum Press, New York, 1974). [lo] R. Vanselow and S.Y. Tong, Chemistry and Physics of Solid Surfaces (CRC press, 1977). [ 1 l] T. Tanabe and S. Imoto, to be published.
Tetsuo Tanabe and Shizsuke Imoto Department of Nuclear Engineering, Faculty of Engineering, Osaka University, Yamadakami, Suita, Osaka,Japan