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Nitrogen recoil chromium implantation into SAE 1020 steel by means of ion beam or plasma immersion ion implantation
Surface & Coatings Technology 196 (2005) 275 – 278 www.elsevier.com/locate/surfcoat
Nitrogen recoil chromium implantation into SAE 1020 steel by means of ion beam or plasma immersion ion implantation G.F. Gomesa, M. Uedaa,*, H. Reutherb, E. Richterb, A.F. Belotoc a
Laborato´rio Associado de Plasma, LAP-INPE, Sa˜o Jose´ dos Campos-SP, Brazil b Forschungszentrum Rossendorf, FZR, Dresden, Germany c Laborato´rio Associado de Materiais e Sensores, LAS-INPE, Sa˜o Jose´ dos Campos, Brazil Available online 19 September 2004
Abstract As an effort to improve the corrosion behavior of the mild steel under work conditions, we attempted to produce a high chromium content layer on its surface by applying the recoil implantation process. After polishing, SAE 1020 construction steel samples were covered with chromium and then bombarded with ions. As recoil bombarding atom, we used nitrogen, a light mass specimen. Recoil atoms were applied either by ion beam (IB) accelerator or by plasma immersion ion implantation (PIII) method. Samples treated by the PIII process showed better results, presenting a thicker layer of high Cr content, as measured by Auger electron spectroscopy (AES). The presence of nitrogen, from hitting process, caused little effect on the surface hardness, as SAE 1020 steel is not suitable for nitriding hardening. Corrosion tests of the PIII-treated samples showed significant enhancement in the steel behaviour under chloride medium attack. D 2004 Elsevier B.V. All rights reserved. PACS: 52.77.Dq; 81.15.Jj; 61.82.Bg; 61.72.Ww; 81.65.Kn; 81.70.Jb Keywords: Plasma immersion ion implantation; SAE 1020 steel; Construction steel; Corrosion; AES
1. Introduction SAE 1020 is one of the most commonly used plain carbon steels, mainly as mortar reinforcement in buildings and small machine parts, as bolts, screws, gears, etc. [1– 4]. However, aside from good mechanical properties as strength, ductility, weldability and machinability, its surface is prone to severe corrosion rates. Due to its modest surface hardness, the high wear rates preclude its use as parts where the wear plays an important role. It has a nominal carbon content of 0.20% and Fe to balance, aside from little amounts of Mg, S and P. As is well known, the presence of chromium (Cr) in excess of 12% in the Fe alloys turns them resistant to several corrosive attacks. As
* Corresponding author. Tel.: +55 12 3945 6676; fax: +55 12 3945 6710. E-mail address: [email protected] (M. Ueda). 0257-8972/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2004.08.107
a rough estimate, about 4% of the USA Gross National Product are costs dealing with corrosion protection products and procedures. Therefore, in this work, we proposed to introduce Cr in such amounts into the surface of SAE 1020 steel. Cr films of 5, 15 and 50 nm were deposited by electron beam process. By bombarding the Cr film either by nitrogen plasma immersion ion implantation (PIII) [5] or nitrogen ion beam (IB), Cr atoms were recoil introduced into the Fe matrix. Normally, in the recoil process, heavy atoms are used, but in this set of experiments, we used a relatively lighter atom, viz. nitrogen [4,6]. SRIM [7] code simulation was used to calculate the range of the Cr atoms into the steel surface after being hit by nitrogen atoms. The energy transferred to the Cr atoms is great enough to implant them by recoil process, even at low energies, as those from a PIII at 10 kV. The surfaces treated by these processes were analyzed to confirm the Cr implantation and some of their new properties, for instance, corrosion enhancement and hard-
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ness. Although not being suitable for nitriding hardening, nitrogen implanted during the recoil Cr implantation may increase the surface hardness and wear resistance (yet to be confirmed by hardness measurements in progress). Further corrosion tests are being carried out in order to measure corrosion properties of the chromium implanted surfaces.
2. Experimental SAE 1020 steel bars as received were prepared as sample disks of 15 mm diameter and 3 mm thickness, polished to 1 Am with alumina powder and then cleaned in acetone bath. Chromium films of thickness of 5, 15 and 50 nm were deposited on samples surface, in a 5 keV electron beam Edwards FL 400 Auto 306 Cryo device. These samples were bombarded either by N+ ion beam (IB) or by nitrogen plasma immersion ion implantation (PIII). In Fig. 1, the atomic concentration profile of these Cr films is presented. Oxygen is present in the film, as impurity from pumping system. In the case of the ion beam treatment, we used 100 keV N+ to a fluence of about 51017 N/cm2, with no temperature control. In the case of plasma immersion ion implantation, we bombarded the samples using two different high voltage pulses: (1) 10 kV, 50 As pulse duration, 300 Hz repetition rate in a glow discharge nitrogen plasma at 810 2 Pa. (2) In the second PIII treatment, we used 40 kV, 5 As pulse duration and 400 Hz repetition rate in a RF discharge nitrogen plasma; both to fluences about 51017 N/cm2, calculated after AES results. To determine the Cr range in the Fe matrix, depth profiling was performed with Auger electron spectroscopy (AES) measurements, in a FISONS Instruments Surface Science, MICROLAB 310-F apparatus, applying sensitivity factors to determine depth. Corrosion tests are under way, in
Fig. 1. Electron beam deposited 30 nm depth chromium film profile on SAE 1020.
Table 1 SRIM and AES results on nitrogen bombarding chromium recoil implantation into SAE 1020 steel Bombarding process
N IB at 100 keV
N PIII at 10 kV
N PIII at 40 kV
Remarks
Cr film thickness Energy to Cr atom (SRIM), from N+ SRIM projected N maximum range (nm) AES measured N maximum range (nm) SRIM projected Cr maximum range (nm) AES measured Cr maximum range (nm)
50 nm
5 or 15 nm
50 nm
e-beam deposited
22 keV/ion
5.9 keV/ion
13.2 keV/ion
195
30
80
185
110
115
20
9
15
20
null
115
a PAR EG&G system. Hardness tests are being carried out in a NanoScience nanoindenter.
3. Results and comments Numerical simulations were carried out using SRIM 2000 code, showing the range of Cr and N atoms in Cr/Fe region, where the presence of Cr film was taken into account (Table 1). In this table, results of AES are also presented, for comparison with theoretical results. As can be seen in the table, SRIM simulation of chromium implantation using nitrogen IB bombardment at 100 keV on Cr film of 50 nm predicted maximum range of about 20 nm to Cr atoms. This result was confirmed by AES data, but in an inhomogeneous profile, as can be seen in Fig. 2. Probably, the energy of nitrogen ion beam at 100 keV was
Fig. 2. Chromium and nitrogen profile of SAE 1020 with 50 nm Cr film after 100 keV ion beam.
G.F. Gomes et al. / Surface & Coatings Technology 196 (2005) 275–278
too large, compelling the N+ ions to cross the Cr film, and despite of a 30% Cr maximum content measured in the region just beneath the interface between the Cr film and the steel, Cr atoms lie mainly in a very thin layer, less than 8 nm. Nitrogen ranges were nearly equal in the simulation and AES results, about 190 nm (Fig. 2). After applying PIII at 10 kV, over a 5 or 15 nm Cr film, no Cr was encountered, albeit a projected range of about 9 nm in the Fe matrix. It was found neither in the Fe matrix nor in the surface. The initially deposited Cr film was removed by sputtering during the process. Nitrogen range from SRIM simulation was about 30 nm and AES results showed 110 nm maximum N ranges (Fig. 3). SRIM simulation of 40 keV N+ bombardment, over a 50 nm Cr film, showed maximum Cr range of about 15 nm, but AES profiles of the samples treated by nitrogen PIII at 40 kV showed ranges as large as 115 nm, evidencing little losses of Cr during the process, the best result so far. Percentages over 12% Cr in a layer ranging for more than 90 nm from the surface were encountered. For this case, nitrogen range from SRIM simulation was about 80 nm and the AES results showed 115 nm maximum N range, as can be seen in Fig. 4. Preliminary corrosion analysis results showed an increase in the corrosion potential of the reference sample and the only Cr film treated, about 430 to 370 mV to the IB-treated and to 330 mV to the PIII-treated sample, all measures referring to standard calomel electrode, SCE. This is a clear trend to more noble behaviour under corrosion attack. Corrosion medium was NaCl 0.66 M, pH 6.0 aerated solution. This result showed no difference between nontreated sample and the only Cr-deposited one. Oxygen, arising from pumping system is also implanted during PIII or IB processes, being beneficial to the surface, as a thin layer of Cr oxide can be created, acting as passivated layer. Preliminary nano-hardness test results showed only modest increase in the surface hardness of the samples treated by PIII at 40 kV and by IB at 100 keV, evidencing
277
Fig. 4. Chromium and nitrogen profile of SAE 1020 with 50 nm Cr film after 40 kV PIII.
the non-nitriding suitability of the SAE 1020 at this range of energies and treatment temperatures. Also, the presence of Cr caused no noticeable increase in the surface hardness.
4. Conclusion As an effort to enhance the corrosion resistance of SAE 1020 steel, we tried to introduce a suitable amount of Cr in its surface. As is well known, anticorrosive effect can be obtained when Cr is in excess of 12% in an iron matrix. Cr films of several thicknesses were deposited on SAE 1020 surface and then bombarded by nitrogen ions. Some samples were ion-bombarded in a 100 keV N+ ion beam machine, and other in a nitrogen plasma immersion ion implantation (PIII) chamber, at 10 or 40 kV. Samples treated at 40 kV PIII showed very promising Cr recoil implantation results, while ones treated with 100 keV ion beam showed more modest results. PIII at 10 kV showed only nitrogen implantation. The absence of Cr would be ascribed to sputtering effect on the thin 15 nm Cr film. Preliminary results of corrosion tests showed great enhancement of the samples treated by PIII and more modest enhancement of the samples treated by IB in the behaviour of the SAE 1020 under corrosive attack in chloride medium. It seems that the presence of oxygen in the treated surfaces are beneficial, creating a barrier to the corrosion process. Even after Cr intake, hardness tests under way showed no significant increase in the surface hardness, as this steel is not suitable for nitriding hardening.
Acknowledgement Fig. 3. Nitrogen profile of SAE 1020 with 5 nm Cr film after 10 kV PIII (no Cr was implanted).
This work is partially funded by FAPESP, to whom G.F. Gomes thanks a postdoctoral fellowship.
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G.F. Gomes et al. / Surface & Coatings Technology 196 (2005) 275–278
References [1] [2] [3] [4]
R. Capozucca, Constr. Build. Mater. 9 (5) (1995) 295. C. Andrade, C. Alonso, Constr. Build. Mater. 15 (2001) 141. H. Agerskov, J. Constr. Steel Res. 53 (2000) 283. A. Anders, S. Anders, I.G. Brown, K.M. Yu, Nucl. Instrum. Methods Phys. Res., B Beam Interact. Mater. Atoms 102 (1995) 132.
[5] M. Ueda, L.A. Berni, G.F. Gomes, A.F. Beloto, E. Abramof, H. Reuther, J. Appl. Phys. 86 (9) (1999) 4821. [6] Z.-C. Wu, Y.-L. Liu, M.-C. Chen, Thin Solid Films 358 (2000) 180. [7] J.F. Ziegler, J.P. Biersack, Stop and Range of Ions in Matter, SRIM, IBM 2002.
Nitrogen recoil chromium implantation into SAE 1020 steel by means of ion beam or plasma immersion ion implantation G.F. Gomesa, M. Uedaa,*, H. Reutherb, E. Richterb, A.F. Belotoc a
Laborato´rio Associado de Plasma, LAP-INPE, Sa˜o Jose´ dos Campos-SP, Brazil b Forschungszentrum Rossendorf, FZR, Dresden, Germany c Laborato´rio Associado de Materiais e Sensores, LAS-INPE, Sa˜o Jose´ dos Campos, Brazil Available online 19 September 2004
Abstract As an effort to improve the corrosion behavior of the mild steel under work conditions, we attempted to produce a high chromium content layer on its surface by applying the recoil implantation process. After polishing, SAE 1020 construction steel samples were covered with chromium and then bombarded with ions. As recoil bombarding atom, we used nitrogen, a light mass specimen. Recoil atoms were applied either by ion beam (IB) accelerator or by plasma immersion ion implantation (PIII) method. Samples treated by the PIII process showed better results, presenting a thicker layer of high Cr content, as measured by Auger electron spectroscopy (AES). The presence of nitrogen, from hitting process, caused little effect on the surface hardness, as SAE 1020 steel is not suitable for nitriding hardening. Corrosion tests of the PIII-treated samples showed significant enhancement in the steel behaviour under chloride medium attack. D 2004 Elsevier B.V. All rights reserved. PACS: 52.77.Dq; 81.15.Jj; 61.82.Bg; 61.72.Ww; 81.65.Kn; 81.70.Jb Keywords: Plasma immersion ion implantation; SAE 1020 steel; Construction steel; Corrosion; AES
1. Introduction SAE 1020 is one of the most commonly used plain carbon steels, mainly as mortar reinforcement in buildings and small machine parts, as bolts, screws, gears, etc. [1– 4]. However, aside from good mechanical properties as strength, ductility, weldability and machinability, its surface is prone to severe corrosion rates. Due to its modest surface hardness, the high wear rates preclude its use as parts where the wear plays an important role. It has a nominal carbon content of 0.20% and Fe to balance, aside from little amounts of Mg, S and P. As is well known, the presence of chromium (Cr) in excess of 12% in the Fe alloys turns them resistant to several corrosive attacks. As
* Corresponding author. Tel.: +55 12 3945 6676; fax: +55 12 3945 6710. E-mail address: [email protected] (M. Ueda). 0257-8972/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2004.08.107
a rough estimate, about 4% of the USA Gross National Product are costs dealing with corrosion protection products and procedures. Therefore, in this work, we proposed to introduce Cr in such amounts into the surface of SAE 1020 steel. Cr films of 5, 15 and 50 nm were deposited by electron beam process. By bombarding the Cr film either by nitrogen plasma immersion ion implantation (PIII) [5] or nitrogen ion beam (IB), Cr atoms were recoil introduced into the Fe matrix. Normally, in the recoil process, heavy atoms are used, but in this set of experiments, we used a relatively lighter atom, viz. nitrogen [4,6]. SRIM [7] code simulation was used to calculate the range of the Cr atoms into the steel surface after being hit by nitrogen atoms. The energy transferred to the Cr atoms is great enough to implant them by recoil process, even at low energies, as those from a PIII at 10 kV. The surfaces treated by these processes were analyzed to confirm the Cr implantation and some of their new properties, for instance, corrosion enhancement and hard-
276
G.F. Gomes et al. / Surface & Coatings Technology 196 (2005) 275–278
ness. Although not being suitable for nitriding hardening, nitrogen implanted during the recoil Cr implantation may increase the surface hardness and wear resistance (yet to be confirmed by hardness measurements in progress). Further corrosion tests are being carried out in order to measure corrosion properties of the chromium implanted surfaces.
2. Experimental SAE 1020 steel bars as received were prepared as sample disks of 15 mm diameter and 3 mm thickness, polished to 1 Am with alumina powder and then cleaned in acetone bath. Chromium films of thickness of 5, 15 and 50 nm were deposited on samples surface, in a 5 keV electron beam Edwards FL 400 Auto 306 Cryo device. These samples were bombarded either by N+ ion beam (IB) or by nitrogen plasma immersion ion implantation (PIII). In Fig. 1, the atomic concentration profile of these Cr films is presented. Oxygen is present in the film, as impurity from pumping system. In the case of the ion beam treatment, we used 100 keV N+ to a fluence of about 51017 N/cm2, with no temperature control. In the case of plasma immersion ion implantation, we bombarded the samples using two different high voltage pulses: (1) 10 kV, 50 As pulse duration, 300 Hz repetition rate in a glow discharge nitrogen plasma at 810 2 Pa. (2) In the second PIII treatment, we used 40 kV, 5 As pulse duration and 400 Hz repetition rate in a RF discharge nitrogen plasma; both to fluences about 51017 N/cm2, calculated after AES results. To determine the Cr range in the Fe matrix, depth profiling was performed with Auger electron spectroscopy (AES) measurements, in a FISONS Instruments Surface Science, MICROLAB 310-F apparatus, applying sensitivity factors to determine depth. Corrosion tests are under way, in
Fig. 1. Electron beam deposited 30 nm depth chromium film profile on SAE 1020.
Table 1 SRIM and AES results on nitrogen bombarding chromium recoil implantation into SAE 1020 steel Bombarding process
N IB at 100 keV
N PIII at 10 kV
N PIII at 40 kV
Remarks
Cr film thickness Energy to Cr atom (SRIM), from N+ SRIM projected N maximum range (nm) AES measured N maximum range (nm) SRIM projected Cr maximum range (nm) AES measured Cr maximum range (nm)
50 nm
5 or 15 nm
50 nm
e-beam deposited
22 keV/ion
5.9 keV/ion
13.2 keV/ion
195
30
80
185
110
115
20
9
15
20
null
115
a PAR EG&G system. Hardness tests are being carried out in a NanoScience nanoindenter.
3. Results and comments Numerical simulations were carried out using SRIM 2000 code, showing the range of Cr and N atoms in Cr/Fe region, where the presence of Cr film was taken into account (Table 1). In this table, results of AES are also presented, for comparison with theoretical results. As can be seen in the table, SRIM simulation of chromium implantation using nitrogen IB bombardment at 100 keV on Cr film of 50 nm predicted maximum range of about 20 nm to Cr atoms. This result was confirmed by AES data, but in an inhomogeneous profile, as can be seen in Fig. 2. Probably, the energy of nitrogen ion beam at 100 keV was
Fig. 2. Chromium and nitrogen profile of SAE 1020 with 50 nm Cr film after 100 keV ion beam.
G.F. Gomes et al. / Surface & Coatings Technology 196 (2005) 275–278
too large, compelling the N+ ions to cross the Cr film, and despite of a 30% Cr maximum content measured in the region just beneath the interface between the Cr film and the steel, Cr atoms lie mainly in a very thin layer, less than 8 nm. Nitrogen ranges were nearly equal in the simulation and AES results, about 190 nm (Fig. 2). After applying PIII at 10 kV, over a 5 or 15 nm Cr film, no Cr was encountered, albeit a projected range of about 9 nm in the Fe matrix. It was found neither in the Fe matrix nor in the surface. The initially deposited Cr film was removed by sputtering during the process. Nitrogen range from SRIM simulation was about 30 nm and AES results showed 110 nm maximum N ranges (Fig. 3). SRIM simulation of 40 keV N+ bombardment, over a 50 nm Cr film, showed maximum Cr range of about 15 nm, but AES profiles of the samples treated by nitrogen PIII at 40 kV showed ranges as large as 115 nm, evidencing little losses of Cr during the process, the best result so far. Percentages over 12% Cr in a layer ranging for more than 90 nm from the surface were encountered. For this case, nitrogen range from SRIM simulation was about 80 nm and the AES results showed 115 nm maximum N range, as can be seen in Fig. 4. Preliminary corrosion analysis results showed an increase in the corrosion potential of the reference sample and the only Cr film treated, about 430 to 370 mV to the IB-treated and to 330 mV to the PIII-treated sample, all measures referring to standard calomel electrode, SCE. This is a clear trend to more noble behaviour under corrosion attack. Corrosion medium was NaCl 0.66 M, pH 6.0 aerated solution. This result showed no difference between nontreated sample and the only Cr-deposited one. Oxygen, arising from pumping system is also implanted during PIII or IB processes, being beneficial to the surface, as a thin layer of Cr oxide can be created, acting as passivated layer. Preliminary nano-hardness test results showed only modest increase in the surface hardness of the samples treated by PIII at 40 kV and by IB at 100 keV, evidencing
277
Fig. 4. Chromium and nitrogen profile of SAE 1020 with 50 nm Cr film after 40 kV PIII.
the non-nitriding suitability of the SAE 1020 at this range of energies and treatment temperatures. Also, the presence of Cr caused no noticeable increase in the surface hardness.
4. Conclusion As an effort to enhance the corrosion resistance of SAE 1020 steel, we tried to introduce a suitable amount of Cr in its surface. As is well known, anticorrosive effect can be obtained when Cr is in excess of 12% in an iron matrix. Cr films of several thicknesses were deposited on SAE 1020 surface and then bombarded by nitrogen ions. Some samples were ion-bombarded in a 100 keV N+ ion beam machine, and other in a nitrogen plasma immersion ion implantation (PIII) chamber, at 10 or 40 kV. Samples treated at 40 kV PIII showed very promising Cr recoil implantation results, while ones treated with 100 keV ion beam showed more modest results. PIII at 10 kV showed only nitrogen implantation. The absence of Cr would be ascribed to sputtering effect on the thin 15 nm Cr film. Preliminary results of corrosion tests showed great enhancement of the samples treated by PIII and more modest enhancement of the samples treated by IB in the behaviour of the SAE 1020 under corrosive attack in chloride medium. It seems that the presence of oxygen in the treated surfaces are beneficial, creating a barrier to the corrosion process. Even after Cr intake, hardness tests under way showed no significant increase in the surface hardness, as this steel is not suitable for nitriding hardening.
Acknowledgement Fig. 3. Nitrogen profile of SAE 1020 with 5 nm Cr film after 10 kV PIII (no Cr was implanted).
This work is partially funded by FAPESP, to whom G.F. Gomes thanks a postdoctoral fellowship.
278
G.F. Gomes et al. / Surface & Coatings Technology 196 (2005) 275–278
References [1] [2] [3] [4]
R. Capozucca, Constr. Build. Mater. 9 (5) (1995) 295. C. Andrade, C. Alonso, Constr. Build. Mater. 15 (2001) 141. H. Agerskov, J. Constr. Steel Res. 53 (2000) 283. A. Anders, S. Anders, I.G. Brown, K.M. Yu, Nucl. Instrum. Methods Phys. Res., B Beam Interact. Mater. Atoms 102 (1995) 132.
[5] M. Ueda, L.A. Berni, G.F. Gomes, A.F. Beloto, E. Abramof, H. Reuther, J. Appl. Phys. 86 (9) (1999) 4821. [6] Z.-C. Wu, Y.-L. Liu, M.-C. Chen, Thin Solid Films 358 (2000) 180. [7] J.F. Ziegler, J.P. Biersack, Stop and Range of Ions in Matter, SRIM, IBM 2002.