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Surface modification of iron and steel by zirconium or yttrium ion implantation and their electrochemical properties
I
Surface modifkation of iron and steel by zirconium or yttrium ion implantation and their electrochemical properties Masaya Iwaki and Katsuo Takahashi RIK EN, Wake. Saituma Ikpun~
Toshiharu Hayakawa, Makoto Yuasa and Isao Sekine Scienc‘c!University of Tokyo. Nodu I Japan)
Jun Takahashi and K&i&i Terashima Chiba lnstitutc of Techncrlyl?‘, C’hiha /Japan)
B. Vincent Crist Iiakuto Co. Ltd.. Shinjuku. Tokyo IJupan j
A study has been made of the corrosion behaviors of zirconium or yttrium ion implanted iron and Fe-5XCr substrates, and of their surface characterization. Implantations of Zr‘ or Y + ions were carried out with fluences of around (0.1. I) x IO” ions cm-’ at an energy of 100 keV at room temperature. The anodic dissolution behavior of ion-implanted iron or steel electrodes was measured by cyclic voltammetry in a pH S acetate buffer solution. Microscopic characterization of the implanted layers was performed by X-ray photoelectron spectroscopy (XPS) measurements combined with argon sputtering. Suppression of the anodic dissolution of iron is observed for both zirconium and yttrium implantations, and the former is more effective than the latter. It was also found that zirconium implantation into Fe-S%0 alloys has a remarkable effect on the suppression of anodic dissolution. The suppression effects become clearer as the zirconium flucn~ increases. XPS results show that implanted zirconium atoms form a gaussian-like distribution, and in the case of high-fluence zirconium ion implantation, either carbon or oxygen atoms invaded near-surface layers to form a diffusion-like distribution. The binding energy spectra corresponding to C,, and Zr,, suggest that the invading carbon combines with iron to form iron carbides, and the invading oxygen combines with zirconium to form zirconium oxides. In conclusion, implanted zirconium atoms play an important role in the improvement in corrosion resistance ofsteels.
1. laWh&m
Ion implantation, which is useful for changing surface composition, has been applied to fundamental studies of corrosion inhibition of steels (see for example ref. I). In this case, the technique has been used fm the formation of compounds such as nitrides and carbides, and metastable alloys such as Fe-Ti-C amorphous alloys. Iron nitrides prod& by nitrogen implantation into iron at room temperature were crystalline, and suppressed the anodic dissolution of iron during electrochemical treatment [Z]. Carbon implantation is more effective than nitrogen implantation for inhibiting corrosion of iron [2]. Surface alloys produced by metal ion implantation also protect iron from corrosion, and it seems that surface alloy formation is more effective than buried nitride formation. Implantation of tantalum and titanium ions into iron results in an improvement in the corrosion inhibition of iron [3,43. In the case of titanium implantation in iron and steel, carbon atoms invaded the iron surfaces during implantation to form an Fe-
Ti-C amorphous alloy [S, 63. Zirconium and yttrium implantantions are considered to have almost identical effects on the corrosion inhibition of iron as titanium implantation because these atoms have similar prop-
erties. In this study, the effects of zirconium and yttrium implantations on the corrosion inhibition of iron and an Fe-S%Cr alloy were investigated, using threeelectrode cyclic voltammetry. X-ray photoelectron spectroscopy (XPS) measurements combined with argon sputtering were used to determine the chemical composition and bonding states. Experimental results will be discussed along with those of our previous work on titanium implantation.
2. Ex#meaU&Us The substrates used were pure iron (999%) and Fe-S%Cr alloy sheets. Before ion implantation, they
.t*e 1992 -
Elsevier Sequoia. All rights reserved
were mechanically mirror polished using a huffing wheel and ultrasonically cleaned in trichloroethylene. A RIKEN 200 kV low current implanter with a Niel.sen-type ion .source was employed and metal chlorides were kd into a discharge chamber to obtain zirconium and yttrium ions. Ion implantation was carried out with fluences ranging from I x IO’” to 1 x IO” ions cm ’ at an energy of 100 keV. The target temperature was near room temperature for low beam current densities of approximately 0.05 -0.5 PA cm -‘. The pressure during ion implantation was about 1 x IO a Pa and the mass spectra of residual gases showed the appearance of masses of 18, 28. and 44 corresponding to H,, N> or CO, and CO2 respectively. Electrochemical properties of implanted specimens were investigated using multisweep cyclic voltammetry, which is a conventional voltammetric system with a three-electrode-type cell used for investigating the aqueous corrosion behavior of iron or iron-based alloys 14-J. The potential sweep rate and the sweep region in cyclic .. < *t voltammetry were SOmV s ’ and -0.7 to +l.OV 1:s saturated calomel ekctrodc (SCE) respectively. The electrolytic solution used was 0.5 mol cm ’ acetate buffer solution of pH 5. All of the measurements were made at 25aO.l C. XPS measurements were carried out to examine depth profiks of implanted elements, host elements, and clements invading during ion implantation, using an “Sprobe”” surface spectrometer from Surface Science Instruments. X-ray photoelectron spectra were used to estimate the chemical bonding states of elements appearing in implanted layers. The binding energy was calibrated using the three values of 83,%&O.l eV for AI_I~~.~, 1~ __..39 &O.I5 eV for Cu,, and 932.47 +0.07 eV for CU 1pJ.L.
3. Resukmldkm&on
Anodic dissolution and passivation of iron were observed in the electrode potential regions of -0-6 to -0.2 V and +O.l to + I .O V respectively, as shown in the previous work [4]. Figure I shows the peak current density of anodic dissolution I, t:s. the potential sweep cycle N, for pure iron, yttrium-implanted iron and zirconium-implanted iron. I, for pure iron is greater than IO mA cm -’ even at early stages of the sweep cycle, showing that iron easily dissolved into the solution. The results in Fig. I indicate that the anodic dissolution is dependent on the fluence. I, for zirconium or fluence of iron with a yttrium-implanted 3.5 x IO’” ions cm _2 is lower than that for pure iron at sting an improvement in aqueous the early stages, su corrosion resistance resulting from ion implantation. I,.
however, gradually increases as N, increases, and I,, at N, =30 is almost the same as that for an unimplantcd specimen. A comparison of the effects of zirconium and yttrium implantation on corrosion inhibition shows that zirconium implantation is mom effective than yttrium implantation. a tluence of Zirconium implantation with 6 x IO”‘ ions. cm -’ is effective for the suppression of anodk dissolution for N, up to 20. However, I, gradually increases as N, increases, and it is almost the same as that of unimplanted iron at N,=50. At a Ruence of I x IO” ions cm ‘, I, at N,=SO was about 2 mA cm - ’ , which is 0. I times that of unimplanted iron. The extremely low I, is almost the same as that of titanium-implanted iron and is one of the lowest I,, values seen in our research. ure 2 shows 1, as H function of N, for unimplanted and zirconium-implanted Fe 5”inCr alloys. The saturated I,, for an unimplanted Fe .S?~$Cralloy is about ImAcm ‘$ which is 20 times lower as that for pure iron. and is similar to that for zirconium-implanted iron with a fluence of I x 10” ions cm ’ at N,=20. At a fhrence of 3.5 x 10rh ions cm ‘. I, at the early stage of N, and at IV,= IO is approximately 0.3 and 0.1 times that for an unimplanted specimen respectively. At a tluence of 6 x 10lh ions cm ‘. I, was 0.04 and 0.06 mA cm ’ at N,= IO and 20 respectively. The saturated I, for zirconium-implanted Fe-S?,CCr alloys is almost the same as that of an Fe IO%Cr alky [73. These results suggest that zirconium implantation of a low fluence in an Fe-Cr alloy with a lower chromium content is useful for obtaining the same properties of anodic dissolution as a higher chromium content alloy. 3.2. Depth distribution t?fcompo,sitions of’impltnted lqwrs
Yttrium atoms implanted in iron with a ftuence of 3.S x IO’” ions cm ” ’ formed a gaussian-like distribution
hf. lwaki et al. / Surjiacemdijication
ofironand steel
Sputtering
Numberof potmtial
swwp cycles
NC
Fig. 2. Relationship between I, and N, for unimphmted ( implanted Fe-S%Cr alloys: V 3.5 x lOi6 Zr cmW2, A 5 x IO” Zr cm-“, t-l 6 x IO’” Zr cm-*.
predicted by LSS theory and measured by Rutherford backscattering and XPS combined with argon sputtering. There were a Few carbon or oxygen atoms on the implanted surface. For zirconium implantation with the same fluence, hardly any carbon or oxygen invasion wa3 found. In some cases of high-fluence zirconium implantation, additional implantations were carried out repeatedly to obtain a desired fluence. The specimen had been exposed to n&dual gases for a long time before and/or during ion implantation. As a result, the color of some samples changed from metallic-luster to gold. XPS measurements were carried out fol both samples, and a large amount of carbon or oxygen atoms was found to have invaded the specimens with metallic-luster or gold color respectively. For a metallic-luster specimen, Fig. 3 shows the depth prtiles of iron, zirconium, carbon and oxygen in zirconiurn-implanted iron with a fluence of 6 x lOi ions cmW2, measured by XPS combined with argon sputtering, Implanted zirconium atoms form a gaussian-like distribution, as predicted theoretically. The carbon invasion is a w not predicted by colli3ion effects alone. Large amounts of carbon atom3 were found to invade the near-surflayers, as in the case of titanium implantation into iron [S-9]. This w should not appear at low fluence ion implantation, which does not calkse sputter-removal of surface native oxides. After removal of the surface oxides, carbon atom3 formed surface layers as a result of carbon absorption and its chemical reaction on the surface. Con3equently, carbon atoms impinged on the surface layers by recoil implantation and knock-on doped carbon atom3 diffused into
3
Time
(34x)
Fig. 3. Atomic percentagc of Fe (O), Zr (0). C (h) and 0 (LI)as a function of argon sputtering time determined by XPS of zirconiumimplanted iron with a Ruence of 6 x lOI Zr cm-“.
deepef regions of the iron, a3 seen for titanium implantation 193. Carbon invasion did not occur for gold colored specimen3. Figure 4 shows the depth pro&s of iron, chromium, zirconium, carbon and oxygen in a zirconium implanted Fe-S%0 alloy at a fluence of 6 x lOi ion3 cm -2. The depth pro& of zirconium is a gaussian-like distribution and a significant reduction in iron content takes place in zirconium-implanted layers. Instead of carbon invasion, it is found that a large amount of oxygen atom3 invades the zirconiumimplanted layers to form a diffusion-like di3tributioq which is similar to the distribution of carbon atom3 invading surface layers of the metallic-luster specimen3. The gold-colored iron induced by zirconium imphtation is due to the invasion of oxygen atoms. The invasion
Sputtering
Time (sac)
Fig.4. Atomic percentage of Fe (0). Zr (0). Cr (A), C (h) and 0 (U) as a function of argon sputtering time determined by XPS of zirconium-implanted Fe-S%0 alloy with a Rueme of 6 xlOlb Zr cmW2.
r-
-7
---------
kd
190
Binding
Energy
(eV)
1
185
Binding
180
Energy
175
(eV)
I M. Iwaki, CRC Crit. Rec. Solid Sfute Ma&r. Sri., 1.5(1989) 473. 2 T. Fujihana, A. Sekiguchi, Y. Okabe, K. Takahashi and M. Iwaki, St@ Cwt. Technd, 51(1992) 19-23. 3 H. Ferber, G. K. Wolf. H. Schmiedel and G. Dearnalay, Murer. Sci. Eng.. 69 (1985) 261. 4 Y. Okabe. M. Iwaki, K. Takahashi and K. Yoshida, Jpn. J. Appl. Php.. 22 (1983) Ll6S.
5 I. L. Singer, J. C’ac.Sci. Tedma/. A. I ( 1983) 419. 6 J. A. Knapp, D. M. Follstaedt and B. L. Doyle. Nucl. Instrum. Methods B, 7-R (1985) 38. 7 T. Hayakawa, J.Takahashi, M. Yuasa, I. Sekine, M. lwaki and K. Takahashi, to be submitted. 8 Y. Fukui, Y. Hirose and M. Iwaki, Thin SdIid Films, 176 (1989) 165. 9 M. Iwaki, K. Yabe, M. Suzuki and 0. Nishimura, Nucl. bstrum. IO M. Iwaki, ltmics, in the press.
Surface modifkation of iron and steel by zirconium or yttrium ion implantation and their electrochemical properties Masaya Iwaki and Katsuo Takahashi RIK EN, Wake. Saituma Ikpun~
Toshiharu Hayakawa, Makoto Yuasa and Isao Sekine Scienc‘c!University of Tokyo. Nodu I Japan)
Jun Takahashi and K&i&i Terashima Chiba lnstitutc of Techncrlyl?‘, C’hiha /Japan)
B. Vincent Crist Iiakuto Co. Ltd.. Shinjuku. Tokyo IJupan j
A study has been made of the corrosion behaviors of zirconium or yttrium ion implanted iron and Fe-5XCr substrates, and of their surface characterization. Implantations of Zr‘ or Y + ions were carried out with fluences of around (0.1. I) x IO” ions cm-’ at an energy of 100 keV at room temperature. The anodic dissolution behavior of ion-implanted iron or steel electrodes was measured by cyclic voltammetry in a pH S acetate buffer solution. Microscopic characterization of the implanted layers was performed by X-ray photoelectron spectroscopy (XPS) measurements combined with argon sputtering. Suppression of the anodic dissolution of iron is observed for both zirconium and yttrium implantations, and the former is more effective than the latter. It was also found that zirconium implantation into Fe-S%0 alloys has a remarkable effect on the suppression of anodic dissolution. The suppression effects become clearer as the zirconium flucn~ increases. XPS results show that implanted zirconium atoms form a gaussian-like distribution, and in the case of high-fluence zirconium ion implantation, either carbon or oxygen atoms invaded near-surface layers to form a diffusion-like distribution. The binding energy spectra corresponding to C,, and Zr,, suggest that the invading carbon combines with iron to form iron carbides, and the invading oxygen combines with zirconium to form zirconium oxides. In conclusion, implanted zirconium atoms play an important role in the improvement in corrosion resistance ofsteels.
1. laWh&m
Ion implantation, which is useful for changing surface composition, has been applied to fundamental studies of corrosion inhibition of steels (see for example ref. I). In this case, the technique has been used fm the formation of compounds such as nitrides and carbides, and metastable alloys such as Fe-Ti-C amorphous alloys. Iron nitrides prod& by nitrogen implantation into iron at room temperature were crystalline, and suppressed the anodic dissolution of iron during electrochemical treatment [Z]. Carbon implantation is more effective than nitrogen implantation for inhibiting corrosion of iron [2]. Surface alloys produced by metal ion implantation also protect iron from corrosion, and it seems that surface alloy formation is more effective than buried nitride formation. Implantation of tantalum and titanium ions into iron results in an improvement in the corrosion inhibition of iron [3,43. In the case of titanium implantation in iron and steel, carbon atoms invaded the iron surfaces during implantation to form an Fe-
Ti-C amorphous alloy [S, 63. Zirconium and yttrium implantantions are considered to have almost identical effects on the corrosion inhibition of iron as titanium implantation because these atoms have similar prop-
erties. In this study, the effects of zirconium and yttrium implantations on the corrosion inhibition of iron and an Fe-S%Cr alloy were investigated, using threeelectrode cyclic voltammetry. X-ray photoelectron spectroscopy (XPS) measurements combined with argon sputtering were used to determine the chemical composition and bonding states. Experimental results will be discussed along with those of our previous work on titanium implantation.
2. Ex#meaU&Us The substrates used were pure iron (999%) and Fe-S%Cr alloy sheets. Before ion implantation, they
.t*e 1992 -
Elsevier Sequoia. All rights reserved
were mechanically mirror polished using a huffing wheel and ultrasonically cleaned in trichloroethylene. A RIKEN 200 kV low current implanter with a Niel.sen-type ion .source was employed and metal chlorides were kd into a discharge chamber to obtain zirconium and yttrium ions. Ion implantation was carried out with fluences ranging from I x IO’” to 1 x IO” ions cm ’ at an energy of 100 keV. The target temperature was near room temperature for low beam current densities of approximately 0.05 -0.5 PA cm -‘. The pressure during ion implantation was about 1 x IO a Pa and the mass spectra of residual gases showed the appearance of masses of 18, 28. and 44 corresponding to H,, N> or CO, and CO2 respectively. Electrochemical properties of implanted specimens were investigated using multisweep cyclic voltammetry, which is a conventional voltammetric system with a three-electrode-type cell used for investigating the aqueous corrosion behavior of iron or iron-based alloys 14-J. The potential sweep rate and the sweep region in cyclic .. < *t voltammetry were SOmV s ’ and -0.7 to +l.OV 1:s saturated calomel ekctrodc (SCE) respectively. The electrolytic solution used was 0.5 mol cm ’ acetate buffer solution of pH 5. All of the measurements were made at 25aO.l C. XPS measurements were carried out to examine depth profiks of implanted elements, host elements, and clements invading during ion implantation, using an “Sprobe”” surface spectrometer from Surface Science Instruments. X-ray photoelectron spectra were used to estimate the chemical bonding states of elements appearing in implanted layers. The binding energy was calibrated using the three values of 83,%&O.l eV for AI_I~~.~, 1~ __..39 &O.I5 eV for Cu,, and 932.47 +0.07 eV for CU 1pJ.L.
3. Resukmldkm&on
Anodic dissolution and passivation of iron were observed in the electrode potential regions of -0-6 to -0.2 V and +O.l to + I .O V respectively, as shown in the previous work [4]. Figure I shows the peak current density of anodic dissolution I, t:s. the potential sweep cycle N, for pure iron, yttrium-implanted iron and zirconium-implanted iron. I, for pure iron is greater than IO mA cm -’ even at early stages of the sweep cycle, showing that iron easily dissolved into the solution. The results in Fig. I indicate that the anodic dissolution is dependent on the fluence. I, for zirconium or fluence of iron with a yttrium-implanted 3.5 x IO’” ions cm _2 is lower than that for pure iron at sting an improvement in aqueous the early stages, su corrosion resistance resulting from ion implantation. I,.
however, gradually increases as N, increases, and I,, at N, =30 is almost the same as that for an unimplantcd specimen. A comparison of the effects of zirconium and yttrium implantation on corrosion inhibition shows that zirconium implantation is mom effective than yttrium implantation. a tluence of Zirconium implantation with 6 x IO”‘ ions. cm -’ is effective for the suppression of anodk dissolution for N, up to 20. However, I, gradually increases as N, increases, and it is almost the same as that of unimplanted iron at N,=50. At a Ruence of I x IO” ions cm ‘, I, at N,=SO was about 2 mA cm - ’ , which is 0. I times that of unimplanted iron. The extremely low I, is almost the same as that of titanium-implanted iron and is one of the lowest I,, values seen in our research. ure 2 shows 1, as H function of N, for unimplanted and zirconium-implanted Fe 5”inCr alloys. The saturated I,, for an unimplanted Fe .S?~$Cralloy is about ImAcm ‘$ which is 20 times lower as that for pure iron. and is similar to that for zirconium-implanted iron with a fluence of I x 10” ions cm ’ at N,=20. At a fhrence of 3.5 x 10rh ions cm ‘. I, at the early stage of N, and at IV,= IO is approximately 0.3 and 0.1 times that for an unimplanted specimen respectively. At a tluence of 6 x 10lh ions cm ‘. I, was 0.04 and 0.06 mA cm ’ at N,= IO and 20 respectively. The saturated I, for zirconium-implanted Fe-S?,CCr alloys is almost the same as that of an Fe IO%Cr alky [73. These results suggest that zirconium implantation of a low fluence in an Fe-Cr alloy with a lower chromium content is useful for obtaining the same properties of anodic dissolution as a higher chromium content alloy. 3.2. Depth distribution t?fcompo,sitions of’impltnted lqwrs
Yttrium atoms implanted in iron with a ftuence of 3.S x IO’” ions cm ” ’ formed a gaussian-like distribution
hf. lwaki et al. / Surjiacemdijication
ofironand steel
Sputtering
Numberof potmtial
swwp cycles
NC
Fig. 2. Relationship between I, and N, for unimphmted ( implanted Fe-S%Cr alloys: V 3.5 x lOi6 Zr cmW2, A 5 x IO” Zr cm-“, t-l 6 x IO’” Zr cm-*.
predicted by LSS theory and measured by Rutherford backscattering and XPS combined with argon sputtering. There were a Few carbon or oxygen atoms on the implanted surface. For zirconium implantation with the same fluence, hardly any carbon or oxygen invasion wa3 found. In some cases of high-fluence zirconium implantation, additional implantations were carried out repeatedly to obtain a desired fluence. The specimen had been exposed to n&dual gases for a long time before and/or during ion implantation. As a result, the color of some samples changed from metallic-luster to gold. XPS measurements were carried out fol both samples, and a large amount of carbon or oxygen atoms was found to have invaded the specimens with metallic-luster or gold color respectively. For a metallic-luster specimen, Fig. 3 shows the depth prtiles of iron, zirconium, carbon and oxygen in zirconiurn-implanted iron with a fluence of 6 x lOi ions cmW2, measured by XPS combined with argon sputtering, Implanted zirconium atoms form a gaussian-like distribution, as predicted theoretically. The carbon invasion is a w not predicted by colli3ion effects alone. Large amounts of carbon atom3 were found to invade the near-surflayers, as in the case of titanium implantation into iron [S-9]. This w should not appear at low fluence ion implantation, which does not calkse sputter-removal of surface native oxides. After removal of the surface oxides, carbon atom3 formed surface layers as a result of carbon absorption and its chemical reaction on the surface. Con3equently, carbon atoms impinged on the surface layers by recoil implantation and knock-on doped carbon atom3 diffused into
3
Time
(34x)
Fig. 3. Atomic percentagc of Fe (O), Zr (0). C (h) and 0 (LI)as a function of argon sputtering time determined by XPS of zirconiumimplanted iron with a Ruence of 6 x lOI Zr cm-“.
deepef regions of the iron, a3 seen for titanium implantation 193. Carbon invasion did not occur for gold colored specimen3. Figure 4 shows the depth pro&s of iron, chromium, zirconium, carbon and oxygen in a zirconium implanted Fe-S%0 alloy at a fluence of 6 x lOi ion3 cm -2. The depth pro& of zirconium is a gaussian-like distribution and a significant reduction in iron content takes place in zirconium-implanted layers. Instead of carbon invasion, it is found that a large amount of oxygen atom3 invades the zirconiumimplanted layers to form a diffusion-like di3tributioq which is similar to the distribution of carbon atom3 invading surface layers of the metallic-luster specimen3. The gold-colored iron induced by zirconium imphtation is due to the invasion of oxygen atoms. The invasion
Sputtering
Time (sac)
Fig.4. Atomic percentage of Fe (0). Zr (0). Cr (A), C (h) and 0 (U) as a function of argon sputtering time determined by XPS of zirconium-implanted Fe-S%0 alloy with a Rueme of 6 xlOlb Zr cmW2.
r-
-7
---------
kd
190
Binding
Energy
(eV)
1
185
Binding
180
Energy
175
(eV)
I M. Iwaki, CRC Crit. Rec. Solid Sfute Ma&r. Sri., 1.5(1989) 473. 2 T. Fujihana, A. Sekiguchi, Y. Okabe, K. Takahashi and M. Iwaki, St@ Cwt. Technd, 51(1992) 19-23. 3 H. Ferber, G. K. Wolf. H. Schmiedel and G. Dearnalay, Murer. Sci. Eng.. 69 (1985) 261. 4 Y. Okabe. M. Iwaki, K. Takahashi and K. Yoshida, Jpn. J. Appl. Php.. 22 (1983) Ll6S.
5 I. L. Singer, J. C’ac.Sci. Tedma/. A. I ( 1983) 419. 6 J. A. Knapp, D. M. Follstaedt and B. L. Doyle. Nucl. Instrum. Methods B, 7-R (1985) 38. 7 T. Hayakawa, J.Takahashi, M. Yuasa, I. Sekine, M. lwaki and K. Takahashi, to be submitted. 8 Y. Fukui, Y. Hirose and M. Iwaki, Thin SdIid Films, 176 (1989) 165. 9 M. Iwaki, K. Yabe, M. Suzuki and 0. Nishimura, Nucl. bstrum. IO M. Iwaki, ltmics, in the press.