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Corrosion and wear mechanisms of aluminum alloys surface reinforced by multicharged N-implantation
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Corrosion and wear mechanisms of aluminum alloys surface reinforced by multicharged N-implantation S. Thibault a,∗ , E. Hug b a b
ENSICAEN, 6 Bd Maréchal Juin, 14050 Caen, France Laboratoire de Cristallographie et Sciences des Matériaux, ENSICAEN, Université de Caen, CNRS, 6 Bd Maréchal Juin, 14050 Caen, France
a r t i c l e
i n f o
Article history: Received 14 November 2013 Received in revised form 22 March 2014 Accepted 22 March 2014 Available online xxx Keywords: Ion implantation Aluminum alloys Corrosion Tribology Aluminum nitride
a b s t r a c t Samples of Al-1050 and of Al-2024 aluminum alloys were implanted by means of nitrogen multicharged ion beam provided by an ECR source. Wear and corrosion tests were performed in order to qualify and quantify the surface enhancement created by implantation. The tests performed, respectively, using ballon-disk set up and linear polarization technique, combined with SEM observations and correlated with microstructural study already published, made possible the identification of damaging mechanisms of nitrogen implanted aluminum surface. The study underlines the importance which has to be given to the implanted fluence and to the initial microstructure, if a consistent surface improvement is targeted. It is demonstrated in this work that the improvement of wear resistance is strongly linked to the intrinsic properties of the nitride protective layer and not to the initial microstructure which only affects optimum fluence. Corrosion tests reveal inverse tendency. The alloy composition is, in this case, of importance, contrarily to implanted fluencies which do not affect the results. This study also shows that if nitrogen implantation is good for surface resistance, a pit (corrosion) or a crack (wear) of implanted surface causes more damage than corrosion or wear of untreated surface. © 2014 Elsevier B.V. All rights reserved.
Introduction Despite its very low thickness (under one micrometer), protective layers produced thanks to nitrogen implantation in metals allow significant improvement in wear and corrosion resistance, thanks to the formation of interstitial compounds. The identification and characterization of nitride phases has been largely studied [1–12]. The potential of implantation techniques is recognized, and confirmed by other studies containing tribological [6,8,13–16] or corrosion positive results [17–20]. Nevertheless it is difficult to find information about the dose dependence of these improvements, of their life time, and, finally, on the consequences of the fracture of the protective layer. The aim of this paper is to bring some answers to these important questions for an industrial use of implantation. This study follows previous results which have shown that multi-charged nitrogen implantation is an efficient surface treatment for pure aluminum (Al-1050) [21]. Aluminum nitride
∗ Corresponding author. Tel.: +33 231451315/+33 673540329. E-mail addresses: [email protected], thibault [email protected] (S. Thibault).
formation mechanisms during implantation were described, and it was concluded that optimized fluence leads to the formation and coherent growth of AlN, allowing significant improvement in wear resistance. This optimum is reached when stress relaxation occurs during implantation. If experiments on pure aluminum are interesting for microstructural modifications study, it is necessary to confirm the interest of the technique with a widely used aluminum alloy. Al-2024 alloy was chosen for its large range of industrial applications. As it is globally established for other aluminum alloys, Al-2024 is not a good friction partner. From the chemical point of view, despite the passivity of aluminum surface, it is sensitive to intergranular corrosion. With this contribution, we propose to investigate surface reaction of N-implanted 1050 and 2024 alloy when submitted to wear and corrosion. To this end, we present the results of ball-on-disk and electrochemical tests. These results are confronted to nanonindentation data and already published microstructural study [21] to state on the origin of the implanted surface resistance. Then we discuss on mechanisms responsible for the destruction of the protective layer thanks to SEM observations. These observations are correlated to wear rate and corrosion rate measurements. Finally we conclude on the efficiency of multi-charged implantation for
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Please cite this article in press as: S. Thibault, E. Hug, Corrosion and wear mechanisms of aluminum alloys surface reinforced by multicharged N-implantation, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.03.164
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aluminum alloys and on the importance of an optimized implantation depending on the industrial application targeted. Material and methods Samples preparation Al-1050 (Al: 99.5%) and Al-2024 aluminum (see normative composition in Table 1) circular samples (10 mm height and 30 mm diameter) were polished to a mirror grade thanks to SiC grinding paper and using 3 m diamond paste. Sintered bulk aluminum nitride (AlN) with dimension (1 × 20 × 20 mm) was used as received as a reference for hardness and tribological tests. Its insulator property impedes electrochemical experiments. Implantation procedure
Fig. 1. Evolution of the friction coefficient during tribological tests for unimplanted and implanted Al-1050 (dashed lines) and Al-2024 samples (dark lines). Pure AlN friction coefficient is given for comparison.
Nitrogen implantation was performed under secondary vacuum on aluminum samples using a micro-implanter described elsewhere [21], with an average charge of 1.4+ and an acceleration bias voltage of 40 kV. Implantation durations were ranged between 10 and 60 s/cm2 which corresponds to ion fluencies in the range of 5.1017 –3.1018 ions/cm2 . The expected projected range of implanted ions was calculated thanks to S.R.I.M. software [22] and is approximately 120 nm. More details on implantation procedure and implantation profiles can be extracted from previous work of the authors [21]. Mechanical tests Tribological tests were performed with a CSM tribometer, using a 6 mm diameter 100C6 ball. A 0.25 N load was applied during 40 laps of 10 mm radius. The rotation speed was set to 0.1 mm/s. Residual track profiles were determined with profilometry measurements. Superficial hardness profiles were obtained with a MTS XP nanoindentation device using the continuous stiffness measurement mode. On each sample, two matrixes of indents were performed with a Berkovich tip (25 indents; X–Y space: 100 m; indentation depth: 2 m) perpendicularly to the surface. Electrochemical tests Polarization curves of Al-samples were obtained thanks to an electrochemical cell designed for flat specimens, using a conventional three-point electrode set up. Electrolyte was a 30 g/L. NaCl solution. The potential scanning was performed with a scan rate of 0.01 V/s, and was measured using a saturated calomel electrode as a reference electrode. Polarization tests were repeated three times for every implantation condition. Results and discussion Surface properties enhancement Results of tribological tests for Al-1050 and Al-2024 are plotted in Fig. 1. It can be clearly seen that implantation under 40 s/cm2 for Al-1050, and 60 s/cm2 for Al-2024, has almost no effect on the coefficient of friction (COF, measured tangential force to applied normal force ratio) which oscillates, respectively, between 0.8 and 1.6 and 0.8 and 1.2. Depending on the aluminum type, different threshold fluence has to be implanted to see a significant and durable decrease of the COF of Al-1050/100C6 and Al-2024/100C6. Independently of the initial microstructure, this COF is close to the AlN/100C6 COF value during the first 20 laps and slightly goes up as the lap number
Fig. 2. Evolution of the average hardness peak value with the implanted fluence for Al-1050 and Al-2024
increases. These results are in good agreement with other studies [6,8,13,16] which postulate that threshold fluence has to be reached to improve friction behavior of aluminum surface by forming continuous AlN protective layer. Thanks to previous grazing incidence X-ray diffraction results concerning Al-1050 [21] the authors have demonstrated that a low COF consecutive to N-implantation is obtained when stress relaxation occurs. This relaxation can be evidenced by nanoindentation measurements. It corresponds to the fall of the hardness peak of the implanted surface. In the case of Al-2024, the optimized implanted fluence for wear resistance enhancement is a 60 s/cm2 . Under this fluence, implantation-induced stress makes the surface instable and brittle. In fact, despite the triggering of hardness decrease with a 50 s/cm2 observed in Fig. 2, tribological test performed for this fluence shown in Fig. 1 reveals that the protective layer is not stable. In the case of Al-1050 the optimized fluence is 40 s/cm2 . Fig. 3 summarizes the results of the electrochemical experiments. The plot of the logarithm of the intensity versus the working electrode potential allows the identification of the corrosion potential Ecor of tested surfaces. The shift of Ecor toward less electronegative potentials after implantations of both alloys can be interpreted as an ennoblement of the surface. This ennoblement traduces a significant improvement of surface corrosion. Contrarily to wear tests, corrosion tests do not show the necessity of threshold fluence to improve surface resistance. As no influence of the
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Table 1 Composition of Al-1050 and Al-2024 in EN 573-1 standard. Alloy
Cu
Mg
Si
Fe
Mn
Zn
Ti
Cr
Al
Al-2024 Al-1050
3.8–4.9 0.05
1.2–1.8 0.05
0.5 0.25
0.5 0.4
0.3–0.9 0.05
0.25 0.07
0.15 0.05
0.1 –
Rest Rest
Fig. 3. Polarization curves of unimplanted and implanted Al-1050 and Al-2024 in NaCl 30 g/L solution Fig. 5. Cracks of fractured protective layer of implanted sample (here Al-2024)
implanted fluence was observed, samples are only presented as ‘unimplanted’ and ‘implanted’ sample. Even if care must be taken when comparing pure and copper alloyed aluminum, we can suppose, regarding to previous results [21], that AlN, chemically very stable phase, is already superficially present from the 10 s/cm2 fluence. That can explain the precocity of implantation-induced surface protection from corrosion. Since corrosion is only governed by chemical reactions resulting of the contact of different species, mechanical state (implantationinduced stress, see [21]) of the sample surface doesn’t interact in the wrong way. Surface sputtering also plays a role in the protection of the implanted surface from corrosion as it was demonstrated by other study [18]. Fig. 4 represents the shift of the corrosion potential. The dispersion of these measurements traduces the reactivity of the surface which can be directly linked to the surface roughness. One can see that surface reactivity decreases with implantation, which confirms that the surface, smoothed by the sputtering [21], is more chemically stable. Another explanation can be the inhibition
Fig. 4. Corrosion potential measurements performed on unimplanted and implanted Al-1050 and Al-2024 samples
of surfacing crystallographic orientations of the grains, due to AlN superficial layer formation. This hypothesis is very difficult to study because of the impossibility to perform crystallographic orientation identification (with electron back scattered diffraction – EBSD – for example) of irradiated, and consequently highly disturbed and strained [21] surface.
Protective layer deterioration and consequences for the substrate It is also necessary to understand the mechanisms of destruction of the nitrided protective layer. They can be studied thanks to SEM pictures of post-mortem samples and to pertinent data extracted from tribological and corrosion tests. Fig. 5 is a typical SEM observation of implanted samples after tribological tests. Same cracks and wear can be observed for underimplanted samples and samples which underwent prolonged wear test (∼1000 laps). In the first case, fracture of the layer occurs due to the high implantation-induced internal stresses. In the second case, the fracture of the optimized implanted layer (40 s/cm2 and 60 s/cm2 , respectively, for Al-1050 and Al-2024), occurs due to an over external stress. These cracks lead to the creation of particles shown in Fig. 6. Despite its low ability to quantify light elements (like O, C, N), the authors have previously verified that energy dispersive X-ray spectrometry (EDS) is suitable to dissociate implanted and unimplanted areas, by detecting or not the presence of nitrogen. In consequence EDS was used to study the particles revealed by SEM observations. An EDS scan is presented in Fig. 6. Nitrogen atomic concentrations are only presented to distinguish areas with, and without, implanted nitrogen. The center part of the scan, with high nitrogen concentration corresponds to the particle region. The left and right parts correspond to the substrate, not protected anymore. This scan clearly shows that the observed particles are rich in nitrogen and are consequently fragments of the protective nitride layer. These hard particles promote severe three-body abrasive wear. Such cracks are not visible on unimplanted samples where a smooth
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Fig. 6. Abrasive particles formed by the protective layer destruction of Al-2024 implanted sample and nitrogen concentration profile measured with EDS
interface between the ball track and the safe region of the sample can be seen [21]. Fig. 7 sums up the results of wear rates expressed in mm3 /N/m. It indicates that wear is more intense for a cracked underimplanted surface (30 and 50 s/cm2 , respectively, for Al-1050 and Al-2024) than for an unimplanted surface. It also indicates the correspondence between stress relaxation – evidenced by hardness decrease – and the consistent enhancement of wear resistance for optimized implantations (40 and 60 s/cm2 , respectively, for Al-1050 and Al2024). Examination of corrosion patterns (Fig. 8) reveals simple pitting for unimplanted and implanted Al-1050 samples. No significant difference can be established between implanted and unimplanted pitted surface. It is only possible to make out the protective layer on the edge of the pits, which is lightly thicker than the oxide layer present on the unimplanted sample. Implanted and unimplanted Al-2024 corroded samples surface presents significant differences as it can be seen in Fig. 9. On the unimplanted surface, intergranular corrosion is clearly observed. This form of corrosion is typical for the Al–Cu–Mg alloys. Intermetallic Al2 CuMg present at grain boundaries are more electronegative than the solid solution and thus will be preferentially corroded [23,24].
Fig. 8. Corroded area of unimplanted (a) and implanted (b) Al-1050 samples
Table 2 Main results of corrosion tests for implanted and unimplanted Al-1050 and Al-2024; polarization resistance (Rpol ), corrosion intensity (Icor ), corrosion rate (CR) and the shift of Ecor (Ecor ). Sample
Rpol (M)
Icor (A)
C.R. (m/yr)
Ecor (mV)
Al-1050 Al-1050 Al-2024 Al-2024
Unimplanted Implanted Unimplanted Implanted
9.1 31 58 16
2.2 0.54 0.35 1.25
2.39 0.58 0.37 1.36
201
Observations carried out on implanted samples reveal different corroded areas detailed in Fig. 10, and more complex corrosion mechanisms. The first condition for the sodium chloride solution to corrode the surface is to pit the protective layer, as it can be seen in Fig. 10. The pits localize corrosion which creates circular ‘craters’ on the substrate. As mentioned before, the layer is brittle and consequently exhibits cracks after pitting. These cracks lead to decohesion of the protective layer from the substrate. After the local delamination of the protective layer, intergranular corrosion can follow on bulk. It is also important to underline that, except local pit, the protective layer is absolutely free from corrosion. Measurements of polarization resistance Rpol , corrosion current icor , corrosion rate CR and the shift of Ecor due to implantation, Ecor , are presented in Table 2. Rpol is the inverse of the slope of the polarization curve at the cathodic/anodic transition. The Stern–Geary relation [25] was used to calculate icor linked to Rpol with the formula icor = B/Rpol , where B is a constant generally set to 20 mV. CR was obtained thanks to the Faraday law defined in equation 1: CR =
Fig. 7. Wear rate versus implanted fluence for Al-1050 and Al-2024
87
M × icor n×F ××A
(1)
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Fig. 9. Corroded area of unimplanted (a) and implanted (b) Al-2024 sample
where M is the molar mass (26.98 g/mol for Al), n the valency number of the ions involved in the reaction (3 for Al), F is the Faraday constant and is equal to 96,485 C/mol, is the mass density (2.7 g/cm3 for Al), A is the corroded area (1 cm2 for this set-up). The calculated values for unimplanted samples are in good agreement with other studies dealing with corrosion of aluminum alloys in saline solution [24,26,27]. For Al-1050 samples, CR decreases after implantation, confirming the positive effect on corrosion resistance of multi-charged implantation into pure aluminum. It is not so easy to conclude on the results concerning Al-2024. Despite an ennoblement of the surface traduced by a shift of Ecor , the corrosion rate CR increases after implantation. Galvanic corrosion is possible for two materials A and B if, |EcorA − EcorB | > 100 mV, A and B are in contact, and A and B are immersed in an electrolyte [23]. After pitting of the layer, substrate and layer can be considered as two materials A and B, and fulfill the galvanic corrosion conditions (|EcorA − EcorB | = Ecor = 201 mV > 100 mV). The increase of CR can be explained by galvanic corrosion, responsible for the craters formation, and subsequent preferential corrosion of the substrate. Furthermore, this estimated CR is underestimated. In fact, if intergranular corrosion is generalized on the unimplanted surface, the anodic current measured on the implanted sample is coming from the few craters observed by SEM (Fig. 9). The corroded area A should be corrected and consequently lowered. Surface ratio of craters to total surface is typically, for observed corroded Al-2024 implanted samples, ranged between 0.05 and 0.1. It indicates that CR for Al2024 implanted sample is underestimated with a factor 10 to 20. The use of multicharged implantation of Al-2024 can be dramatic if the corrosive media pits the nitrided layer.
5
Fig. 10. The four steps of protective layer corrosion for implanted Al-2024: pitting (a), cracking, galvanic corrosion and preferential intergranular corrosion of the bulk (b)
Conclusion Concerning multicharged N-implantation of Al-1050 and Al2024, the following conclusions can be established: - Multi-charged implantation of nitrogen into Al-1050 and Al-2024 allows a significant decrease of the COF, and a chemical ennoblement of the surface. - For both alloys, threshold fluence is required to change the tribological behavior of the surface (COF decrease). This threshold fluence depends on initial microstructure (composition) and is reached when implantation-induced stress relaxes. Absolute value of the COF (0.2) of optimized implanted surface are linked to intrinsic properties of AlN and not to the bulk ones. - From a chemical point of view, the mechanisms are more complex. In one hand, light fluence is sufficient to ennoble the surface. Ecor is shift from the first steps of protective layer formation and probably thanks to additive effects of sputtering. Increasing fluence has no effect. In the other hand, the corrosion resistance of aluminum alloy is strongly dependent on the alloy composition and especially to the corresponding value of Ecor . A too high Ecor value can lead to an increase of the corrosion rate due to galvanic corrosion. - Multi-charged implantation can produce inverse effects of the ones whished if the protective layer is fractured by mechanical or corrosion stresses. Fractured or pitted protective layer acts as a catalyzer for bulk material deterioration. In the case of wear, the more pronounced deterioration is caused by three-body abrasive wear. In the case of corrosion, it is caused by galvanic preferential corrosion.
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The present study confirms the interest of multi-charged implantation of nitrogen into aluminum alloys. By extension, it seems that every aluminum alloys wear resistance could be improved, since AlN superficial formation is possible. This work also focuses on the problems that could happen if the protective layer is damaged. Generally it underlines that specific care must be taken to optimize N-implantation fluence, depending on the initial microstructure, the kind and the intensity of the external stresses, even more for anti-corrosion applications. References [1] W. Österle, I. Dörfel, I. Urban, T. Reier, J.W. Schultze, XPS and XTEM study of AlN formation by N + 2 implantation of aluminium, Surf. Coat. Technol. 102 (1998) 168–174. [2] S. Ohira, M. Iwaki, Formation of AlN by nitrogen molecule ion implantation, Nucl. Instrum. Methods Phys. Res., Sect. B: Beam Interact. Mater. and At. 19–20 (1987) 162–166. [3] P. Budzynski, A.A. Youssef, Z. Surowiec, R. Paluch, Nitrogen ion implantation for improvement of the mechanical surface properties of aluminum, Vacuum 81 (2007) 1154–1158. [4] R. Figueroa, C.M. Abreu, M.J. Cristobal, G. Pena, Effect of nitrogen and molybdenum ion implantation in the tribological behavior of AA7075 aluminum alloy, Wear 276–277 (2012) 53–60. [5] S. Fukumoto, M. Ando, H. Tsubakino, M. Terasawa, T. Mitamura, Morphology of AlN formed in aluminum by ion implantation, Mater. Chem. Phys. 54 (1998) 351–355. [6] J. Jagielski, A. Piatkowska, P. Aubert, C. Legrand-Buscema, C.L. Paven, G. Gawlik, J. Piekoszewski, Z. Werner, Effects of high dose nitrogen implantation into aluminum, Vacuum 70 (2003) 147–152. [7] T.R. Jervis, H.-L. Lu, J.R. Tesmer, Effect of nitrogen implantation on the surface hardness of pure aluminum and alloy materials, Nucl. Instrum. Methods Phys. Res., Sect. B: Beam Interact. Mater. and At. 72 (1992) 59–63. [8] H.J. Kang, Surface modification of aluminum by N-ion implantation, Int. J. Precis. Eng. Manuf. 7 (2006) 57. [9] E. Leblond, D. Treheux, C. Esnouf, G. Fantozzi, N. Moncoffre, G. Marest, Y. Corre, Elaboration et optimisation de nanopréciprités d’AlN dans une matrice d’aluminium, Mater. Tech. 5–6 (2000). [10] H.L. Lu, W.F. Sommer, M.J. Borden, J.R. Tesmer, X.D. Wu, The microstructure and properties of a buried AIN layer produced by nitrogen implantation into pure aluminum, Thin Solid Films 289 (1996) 17–21.
[11] S. Lucas, J. Chevallier, Computer simulations and transmission electron microscopy investigations of nitrogen implanted into aluminium at high temperature, Surf. Coat. Technol. 51 (1992) 441–445. [12] S. Lucas, J. Chevallier, Nanohardness and transmission electron microscopy study of nitrogen-implanted aluminium, Surf. Coat. Technol. 65 (1994) 128–132. [13] E. Leblond, Nitruration de l’aluminium par voies ioniques, in: Ph.D., Ecole Centrale Lyon, 1998. [14] L. Guzman, G. Bonini, M. Adami, P.M. Ossi, A. Miotello, M. Vittori-Antisari, A.M. Serventi, E. Voltolini, Mechanical behaviour of nitrogen-implanted aluminium alloys, Surf. Coat. Technol. 83 (1996) 284–289. [15] A.A. Youssef, P. Budzynski, J. Filiks, Z. Surowiec, Improvement of tribological properties of aluminum by nitrogen implantation, Vacuum 78 (2005) 599–603. [16] R.J. Rodriguez, A. Sanz, A. Medrano, J. Garcia-Lorente, Tribological properties of ion implanted aluminum alloys, Vacuum 52 (1999) 187–192. [17] K.C. Walter, R.A. Dodd, J.R. Conrad, Corrosion behavior of nitrogen implanted aluminum, Nucl. Instrum. Methods Phys. Res., Sect. B: Beam Interact. Mater. and At. 106 (1995) 522–526. [18] S. Seghrouchni, Caractérisation chimique et structurale de revêtements d’aluminium oxydé et nitruré et étude de leur réactivité électrochimique en milieux acide et chloruré, in: Ph.D., Université Louis Pasteur, Strasbourg, 1996. [19] J.M. Williams, A. Gonzales, J. Quintana, I.S. Lee, R.A. Buchanan, F.C. Burns, R.J. Culbertson, M. Levy, J.R. Treglio, Ion implantation for corrosion inhibition of aluminum alloys in saline media, Nucl. Instrum. Methods Phys. Res., Sect. B: Beam Interact. Mater. and At. 59–60 Part 2 (1991) 845–850. [20] Y. Massiani, J.P. Crousier, L. Fedrizzi, S. Gialanella, P.L. Bonora, Electrochemical study of multiple-energy nitrogen-ion-implanted aluminium alloys, Mater. Sci. Eng., A 116 (1989) 53–57. [21] E. Hug, S. Thibault, D. Chateigner, L. Maunoury, Nitriding aluminum alloys by N-multicharged ions implantation: correlation between surface strengthening and microstructure modifications, Surf. Coat. Technol. 206 (2012) 5028–5035. [22] J.F. Ziegler, M.D. Ziegler, J.P. Biersack, SRIM: the stopping and range of ions in matter, Nucl. Instrum. Methods Phys. Res., Sect. B: Beam Interact. Mater. and At. 268 (2010) 1818–1823. [23] C. Vargel, Corrosion de l’aluminium, Dunod, Paris, 1999. [24] B.B. Wang, Z.Y. Wang, W. Han, W. Ke, Atmospheric corrosion of aluminium alloy 2024-T3 exposed to salt lake environment in Western China, Corros. Sci. 59 (2012) 63–70. [25] M. Stern, A.L. Geary, Electrochemical polarization. 1: A theoretical analysis of the shape of polarization curves, J. Electrochem. Soc. 104 (1957) 56–63. [26] U. Trdan, J. Grum, Evaluation of corrosion resistance of AA6082-T651 aluminium alloy after laser shock peening by means of cyclic polarisation and ElS methods, Corros. Sci. 59 (2012) 324–333. [27] H. Ezuber, A. El-Houd, F. El-Shawesh, A study on the corrosion behavior of aluminum alloys in seawater, Mater. Des. 29 (2008) 801–805.
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Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Corrosion and wear mechanisms of aluminum alloys surface reinforced by multicharged N-implantation S. Thibault a,∗ , E. Hug b a b
ENSICAEN, 6 Bd Maréchal Juin, 14050 Caen, France Laboratoire de Cristallographie et Sciences des Matériaux, ENSICAEN, Université de Caen, CNRS, 6 Bd Maréchal Juin, 14050 Caen, France
a r t i c l e
i n f o
Article history: Received 14 November 2013 Received in revised form 22 March 2014 Accepted 22 March 2014 Available online xxx Keywords: Ion implantation Aluminum alloys Corrosion Tribology Aluminum nitride
a b s t r a c t Samples of Al-1050 and of Al-2024 aluminum alloys were implanted by means of nitrogen multicharged ion beam provided by an ECR source. Wear and corrosion tests were performed in order to qualify and quantify the surface enhancement created by implantation. The tests performed, respectively, using ballon-disk set up and linear polarization technique, combined with SEM observations and correlated with microstructural study already published, made possible the identification of damaging mechanisms of nitrogen implanted aluminum surface. The study underlines the importance which has to be given to the implanted fluence and to the initial microstructure, if a consistent surface improvement is targeted. It is demonstrated in this work that the improvement of wear resistance is strongly linked to the intrinsic properties of the nitride protective layer and not to the initial microstructure which only affects optimum fluence. Corrosion tests reveal inverse tendency. The alloy composition is, in this case, of importance, contrarily to implanted fluencies which do not affect the results. This study also shows that if nitrogen implantation is good for surface resistance, a pit (corrosion) or a crack (wear) of implanted surface causes more damage than corrosion or wear of untreated surface. © 2014 Elsevier B.V. All rights reserved.
Introduction Despite its very low thickness (under one micrometer), protective layers produced thanks to nitrogen implantation in metals allow significant improvement in wear and corrosion resistance, thanks to the formation of interstitial compounds. The identification and characterization of nitride phases has been largely studied [1–12]. The potential of implantation techniques is recognized, and confirmed by other studies containing tribological [6,8,13–16] or corrosion positive results [17–20]. Nevertheless it is difficult to find information about the dose dependence of these improvements, of their life time, and, finally, on the consequences of the fracture of the protective layer. The aim of this paper is to bring some answers to these important questions for an industrial use of implantation. This study follows previous results which have shown that multi-charged nitrogen implantation is an efficient surface treatment for pure aluminum (Al-1050) [21]. Aluminum nitride
∗ Corresponding author. Tel.: +33 231451315/+33 673540329. E-mail addresses: [email protected], thibault [email protected] (S. Thibault).
formation mechanisms during implantation were described, and it was concluded that optimized fluence leads to the formation and coherent growth of AlN, allowing significant improvement in wear resistance. This optimum is reached when stress relaxation occurs during implantation. If experiments on pure aluminum are interesting for microstructural modifications study, it is necessary to confirm the interest of the technique with a widely used aluminum alloy. Al-2024 alloy was chosen for its large range of industrial applications. As it is globally established for other aluminum alloys, Al-2024 is not a good friction partner. From the chemical point of view, despite the passivity of aluminum surface, it is sensitive to intergranular corrosion. With this contribution, we propose to investigate surface reaction of N-implanted 1050 and 2024 alloy when submitted to wear and corrosion. To this end, we present the results of ball-on-disk and electrochemical tests. These results are confronted to nanonindentation data and already published microstructural study [21] to state on the origin of the implanted surface resistance. Then we discuss on mechanisms responsible for the destruction of the protective layer thanks to SEM observations. These observations are correlated to wear rate and corrosion rate measurements. Finally we conclude on the efficiency of multi-charged implantation for
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Please cite this article in press as: S. Thibault, E. Hug, Corrosion and wear mechanisms of aluminum alloys surface reinforced by multicharged N-implantation, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.03.164
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aluminum alloys and on the importance of an optimized implantation depending on the industrial application targeted. Material and methods Samples preparation Al-1050 (Al: 99.5%) and Al-2024 aluminum (see normative composition in Table 1) circular samples (10 mm height and 30 mm diameter) were polished to a mirror grade thanks to SiC grinding paper and using 3 m diamond paste. Sintered bulk aluminum nitride (AlN) with dimension (1 × 20 × 20 mm) was used as received as a reference for hardness and tribological tests. Its insulator property impedes electrochemical experiments. Implantation procedure
Fig. 1. Evolution of the friction coefficient during tribological tests for unimplanted and implanted Al-1050 (dashed lines) and Al-2024 samples (dark lines). Pure AlN friction coefficient is given for comparison.
Nitrogen implantation was performed under secondary vacuum on aluminum samples using a micro-implanter described elsewhere [21], with an average charge of 1.4+ and an acceleration bias voltage of 40 kV. Implantation durations were ranged between 10 and 60 s/cm2 which corresponds to ion fluencies in the range of 5.1017 –3.1018 ions/cm2 . The expected projected range of implanted ions was calculated thanks to S.R.I.M. software [22] and is approximately 120 nm. More details on implantation procedure and implantation profiles can be extracted from previous work of the authors [21]. Mechanical tests Tribological tests were performed with a CSM tribometer, using a 6 mm diameter 100C6 ball. A 0.25 N load was applied during 40 laps of 10 mm radius. The rotation speed was set to 0.1 mm/s. Residual track profiles were determined with profilometry measurements. Superficial hardness profiles were obtained with a MTS XP nanoindentation device using the continuous stiffness measurement mode. On each sample, two matrixes of indents were performed with a Berkovich tip (25 indents; X–Y space: 100 m; indentation depth: 2 m) perpendicularly to the surface. Electrochemical tests Polarization curves of Al-samples were obtained thanks to an electrochemical cell designed for flat specimens, using a conventional three-point electrode set up. Electrolyte was a 30 g/L. NaCl solution. The potential scanning was performed with a scan rate of 0.01 V/s, and was measured using a saturated calomel electrode as a reference electrode. Polarization tests were repeated three times for every implantation condition. Results and discussion Surface properties enhancement Results of tribological tests for Al-1050 and Al-2024 are plotted in Fig. 1. It can be clearly seen that implantation under 40 s/cm2 for Al-1050, and 60 s/cm2 for Al-2024, has almost no effect on the coefficient of friction (COF, measured tangential force to applied normal force ratio) which oscillates, respectively, between 0.8 and 1.6 and 0.8 and 1.2. Depending on the aluminum type, different threshold fluence has to be implanted to see a significant and durable decrease of the COF of Al-1050/100C6 and Al-2024/100C6. Independently of the initial microstructure, this COF is close to the AlN/100C6 COF value during the first 20 laps and slightly goes up as the lap number
Fig. 2. Evolution of the average hardness peak value with the implanted fluence for Al-1050 and Al-2024
increases. These results are in good agreement with other studies [6,8,13,16] which postulate that threshold fluence has to be reached to improve friction behavior of aluminum surface by forming continuous AlN protective layer. Thanks to previous grazing incidence X-ray diffraction results concerning Al-1050 [21] the authors have demonstrated that a low COF consecutive to N-implantation is obtained when stress relaxation occurs. This relaxation can be evidenced by nanoindentation measurements. It corresponds to the fall of the hardness peak of the implanted surface. In the case of Al-2024, the optimized implanted fluence for wear resistance enhancement is a 60 s/cm2 . Under this fluence, implantation-induced stress makes the surface instable and brittle. In fact, despite the triggering of hardness decrease with a 50 s/cm2 observed in Fig. 2, tribological test performed for this fluence shown in Fig. 1 reveals that the protective layer is not stable. In the case of Al-1050 the optimized fluence is 40 s/cm2 . Fig. 3 summarizes the results of the electrochemical experiments. The plot of the logarithm of the intensity versus the working electrode potential allows the identification of the corrosion potential Ecor of tested surfaces. The shift of Ecor toward less electronegative potentials after implantations of both alloys can be interpreted as an ennoblement of the surface. This ennoblement traduces a significant improvement of surface corrosion. Contrarily to wear tests, corrosion tests do not show the necessity of threshold fluence to improve surface resistance. As no influence of the
Please cite this article in press as: S. Thibault, E. Hug, Corrosion and wear mechanisms of aluminum alloys surface reinforced by multicharged N-implantation, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.03.164
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Table 1 Composition of Al-1050 and Al-2024 in EN 573-1 standard. Alloy
Cu
Mg
Si
Fe
Mn
Zn
Ti
Cr
Al
Al-2024 Al-1050
3.8–4.9 0.05
1.2–1.8 0.05
0.5 0.25
0.5 0.4
0.3–0.9 0.05
0.25 0.07
0.15 0.05
0.1 –
Rest Rest
Fig. 3. Polarization curves of unimplanted and implanted Al-1050 and Al-2024 in NaCl 30 g/L solution Fig. 5. Cracks of fractured protective layer of implanted sample (here Al-2024)
implanted fluence was observed, samples are only presented as ‘unimplanted’ and ‘implanted’ sample. Even if care must be taken when comparing pure and copper alloyed aluminum, we can suppose, regarding to previous results [21], that AlN, chemically very stable phase, is already superficially present from the 10 s/cm2 fluence. That can explain the precocity of implantation-induced surface protection from corrosion. Since corrosion is only governed by chemical reactions resulting of the contact of different species, mechanical state (implantationinduced stress, see [21]) of the sample surface doesn’t interact in the wrong way. Surface sputtering also plays a role in the protection of the implanted surface from corrosion as it was demonstrated by other study [18]. Fig. 4 represents the shift of the corrosion potential. The dispersion of these measurements traduces the reactivity of the surface which can be directly linked to the surface roughness. One can see that surface reactivity decreases with implantation, which confirms that the surface, smoothed by the sputtering [21], is more chemically stable. Another explanation can be the inhibition
Fig. 4. Corrosion potential measurements performed on unimplanted and implanted Al-1050 and Al-2024 samples
of surfacing crystallographic orientations of the grains, due to AlN superficial layer formation. This hypothesis is very difficult to study because of the impossibility to perform crystallographic orientation identification (with electron back scattered diffraction – EBSD – for example) of irradiated, and consequently highly disturbed and strained [21] surface.
Protective layer deterioration and consequences for the substrate It is also necessary to understand the mechanisms of destruction of the nitrided protective layer. They can be studied thanks to SEM pictures of post-mortem samples and to pertinent data extracted from tribological and corrosion tests. Fig. 5 is a typical SEM observation of implanted samples after tribological tests. Same cracks and wear can be observed for underimplanted samples and samples which underwent prolonged wear test (∼1000 laps). In the first case, fracture of the layer occurs due to the high implantation-induced internal stresses. In the second case, the fracture of the optimized implanted layer (40 s/cm2 and 60 s/cm2 , respectively, for Al-1050 and Al-2024), occurs due to an over external stress. These cracks lead to the creation of particles shown in Fig. 6. Despite its low ability to quantify light elements (like O, C, N), the authors have previously verified that energy dispersive X-ray spectrometry (EDS) is suitable to dissociate implanted and unimplanted areas, by detecting or not the presence of nitrogen. In consequence EDS was used to study the particles revealed by SEM observations. An EDS scan is presented in Fig. 6. Nitrogen atomic concentrations are only presented to distinguish areas with, and without, implanted nitrogen. The center part of the scan, with high nitrogen concentration corresponds to the particle region. The left and right parts correspond to the substrate, not protected anymore. This scan clearly shows that the observed particles are rich in nitrogen and are consequently fragments of the protective nitride layer. These hard particles promote severe three-body abrasive wear. Such cracks are not visible on unimplanted samples where a smooth
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Fig. 6. Abrasive particles formed by the protective layer destruction of Al-2024 implanted sample and nitrogen concentration profile measured with EDS
interface between the ball track and the safe region of the sample can be seen [21]. Fig. 7 sums up the results of wear rates expressed in mm3 /N/m. It indicates that wear is more intense for a cracked underimplanted surface (30 and 50 s/cm2 , respectively, for Al-1050 and Al-2024) than for an unimplanted surface. It also indicates the correspondence between stress relaxation – evidenced by hardness decrease – and the consistent enhancement of wear resistance for optimized implantations (40 and 60 s/cm2 , respectively, for Al-1050 and Al2024). Examination of corrosion patterns (Fig. 8) reveals simple pitting for unimplanted and implanted Al-1050 samples. No significant difference can be established between implanted and unimplanted pitted surface. It is only possible to make out the protective layer on the edge of the pits, which is lightly thicker than the oxide layer present on the unimplanted sample. Implanted and unimplanted Al-2024 corroded samples surface presents significant differences as it can be seen in Fig. 9. On the unimplanted surface, intergranular corrosion is clearly observed. This form of corrosion is typical for the Al–Cu–Mg alloys. Intermetallic Al2 CuMg present at grain boundaries are more electronegative than the solid solution and thus will be preferentially corroded [23,24].
Fig. 8. Corroded area of unimplanted (a) and implanted (b) Al-1050 samples
Table 2 Main results of corrosion tests for implanted and unimplanted Al-1050 and Al-2024; polarization resistance (Rpol ), corrosion intensity (Icor ), corrosion rate (CR) and the shift of Ecor (Ecor ). Sample
Rpol (M)
Icor (A)
C.R. (m/yr)
Ecor (mV)
Al-1050 Al-1050 Al-2024 Al-2024
Unimplanted Implanted Unimplanted Implanted
9.1 31 58 16
2.2 0.54 0.35 1.25
2.39 0.58 0.37 1.36
201
Observations carried out on implanted samples reveal different corroded areas detailed in Fig. 10, and more complex corrosion mechanisms. The first condition for the sodium chloride solution to corrode the surface is to pit the protective layer, as it can be seen in Fig. 10. The pits localize corrosion which creates circular ‘craters’ on the substrate. As mentioned before, the layer is brittle and consequently exhibits cracks after pitting. These cracks lead to decohesion of the protective layer from the substrate. After the local delamination of the protective layer, intergranular corrosion can follow on bulk. It is also important to underline that, except local pit, the protective layer is absolutely free from corrosion. Measurements of polarization resistance Rpol , corrosion current icor , corrosion rate CR and the shift of Ecor due to implantation, Ecor , are presented in Table 2. Rpol is the inverse of the slope of the polarization curve at the cathodic/anodic transition. The Stern–Geary relation [25] was used to calculate icor linked to Rpol with the formula icor = B/Rpol , where B is a constant generally set to 20 mV. CR was obtained thanks to the Faraday law defined in equation 1: CR =
Fig. 7. Wear rate versus implanted fluence for Al-1050 and Al-2024
87
M × icor n×F ××A
(1)
Please cite this article in press as: S. Thibault, E. Hug, Corrosion and wear mechanisms of aluminum alloys surface reinforced by multicharged N-implantation, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.03.164
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Fig. 9. Corroded area of unimplanted (a) and implanted (b) Al-2024 sample
where M is the molar mass (26.98 g/mol for Al), n the valency number of the ions involved in the reaction (3 for Al), F is the Faraday constant and is equal to 96,485 C/mol, is the mass density (2.7 g/cm3 for Al), A is the corroded area (1 cm2 for this set-up). The calculated values for unimplanted samples are in good agreement with other studies dealing with corrosion of aluminum alloys in saline solution [24,26,27]. For Al-1050 samples, CR decreases after implantation, confirming the positive effect on corrosion resistance of multi-charged implantation into pure aluminum. It is not so easy to conclude on the results concerning Al-2024. Despite an ennoblement of the surface traduced by a shift of Ecor , the corrosion rate CR increases after implantation. Galvanic corrosion is possible for two materials A and B if, |EcorA − EcorB | > 100 mV, A and B are in contact, and A and B are immersed in an electrolyte [23]. After pitting of the layer, substrate and layer can be considered as two materials A and B, and fulfill the galvanic corrosion conditions (|EcorA − EcorB | = Ecor = 201 mV > 100 mV). The increase of CR can be explained by galvanic corrosion, responsible for the craters formation, and subsequent preferential corrosion of the substrate. Furthermore, this estimated CR is underestimated. In fact, if intergranular corrosion is generalized on the unimplanted surface, the anodic current measured on the implanted sample is coming from the few craters observed by SEM (Fig. 9). The corroded area A should be corrected and consequently lowered. Surface ratio of craters to total surface is typically, for observed corroded Al-2024 implanted samples, ranged between 0.05 and 0.1. It indicates that CR for Al2024 implanted sample is underestimated with a factor 10 to 20. The use of multicharged implantation of Al-2024 can be dramatic if the corrosive media pits the nitrided layer.
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Fig. 10. The four steps of protective layer corrosion for implanted Al-2024: pitting (a), cracking, galvanic corrosion and preferential intergranular corrosion of the bulk (b)
Conclusion Concerning multicharged N-implantation of Al-1050 and Al2024, the following conclusions can be established: - Multi-charged implantation of nitrogen into Al-1050 and Al-2024 allows a significant decrease of the COF, and a chemical ennoblement of the surface. - For both alloys, threshold fluence is required to change the tribological behavior of the surface (COF decrease). This threshold fluence depends on initial microstructure (composition) and is reached when implantation-induced stress relaxes. Absolute value of the COF (0.2) of optimized implanted surface are linked to intrinsic properties of AlN and not to the bulk ones. - From a chemical point of view, the mechanisms are more complex. In one hand, light fluence is sufficient to ennoble the surface. Ecor is shift from the first steps of protective layer formation and probably thanks to additive effects of sputtering. Increasing fluence has no effect. In the other hand, the corrosion resistance of aluminum alloy is strongly dependent on the alloy composition and especially to the corresponding value of Ecor . A too high Ecor value can lead to an increase of the corrosion rate due to galvanic corrosion. - Multi-charged implantation can produce inverse effects of the ones whished if the protective layer is fractured by mechanical or corrosion stresses. Fractured or pitted protective layer acts as a catalyzer for bulk material deterioration. In the case of wear, the more pronounced deterioration is caused by three-body abrasive wear. In the case of corrosion, it is caused by galvanic preferential corrosion.
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The present study confirms the interest of multi-charged implantation of nitrogen into aluminum alloys. By extension, it seems that every aluminum alloys wear resistance could be improved, since AlN superficial formation is possible. This work also focuses on the problems that could happen if the protective layer is damaged. Generally it underlines that specific care must be taken to optimize N-implantation fluence, depending on the initial microstructure, the kind and the intensity of the external stresses, even more for anti-corrosion applications. References [1] W. Österle, I. Dörfel, I. Urban, T. Reier, J.W. Schultze, XPS and XTEM study of AlN formation by N + 2 implantation of aluminium, Surf. Coat. Technol. 102 (1998) 168–174. [2] S. Ohira, M. Iwaki, Formation of AlN by nitrogen molecule ion implantation, Nucl. Instrum. Methods Phys. Res., Sect. B: Beam Interact. Mater. and At. 19–20 (1987) 162–166. [3] P. Budzynski, A.A. Youssef, Z. Surowiec, R. Paluch, Nitrogen ion implantation for improvement of the mechanical surface properties of aluminum, Vacuum 81 (2007) 1154–1158. [4] R. Figueroa, C.M. Abreu, M.J. Cristobal, G. Pena, Effect of nitrogen and molybdenum ion implantation in the tribological behavior of AA7075 aluminum alloy, Wear 276–277 (2012) 53–60. [5] S. Fukumoto, M. Ando, H. Tsubakino, M. Terasawa, T. Mitamura, Morphology of AlN formed in aluminum by ion implantation, Mater. Chem. Phys. 54 (1998) 351–355. [6] J. Jagielski, A. Piatkowska, P. Aubert, C. Legrand-Buscema, C.L. Paven, G. Gawlik, J. Piekoszewski, Z. Werner, Effects of high dose nitrogen implantation into aluminum, Vacuum 70 (2003) 147–152. [7] T.R. Jervis, H.-L. Lu, J.R. Tesmer, Effect of nitrogen implantation on the surface hardness of pure aluminum and alloy materials, Nucl. Instrum. Methods Phys. Res., Sect. B: Beam Interact. Mater. and At. 72 (1992) 59–63. [8] H.J. Kang, Surface modification of aluminum by N-ion implantation, Int. J. Precis. Eng. Manuf. 7 (2006) 57. [9] E. Leblond, D. Treheux, C. Esnouf, G. Fantozzi, N. Moncoffre, G. Marest, Y. Corre, Elaboration et optimisation de nanopréciprités d’AlN dans une matrice d’aluminium, Mater. Tech. 5–6 (2000). [10] H.L. Lu, W.F. Sommer, M.J. Borden, J.R. Tesmer, X.D. Wu, The microstructure and properties of a buried AIN layer produced by nitrogen implantation into pure aluminum, Thin Solid Films 289 (1996) 17–21.
[11] S. Lucas, J. Chevallier, Computer simulations and transmission electron microscopy investigations of nitrogen implanted into aluminium at high temperature, Surf. Coat. Technol. 51 (1992) 441–445. [12] S. Lucas, J. Chevallier, Nanohardness and transmission electron microscopy study of nitrogen-implanted aluminium, Surf. Coat. Technol. 65 (1994) 128–132. [13] E. Leblond, Nitruration de l’aluminium par voies ioniques, in: Ph.D., Ecole Centrale Lyon, 1998. [14] L. Guzman, G. Bonini, M. Adami, P.M. Ossi, A. Miotello, M. Vittori-Antisari, A.M. Serventi, E. Voltolini, Mechanical behaviour of nitrogen-implanted aluminium alloys, Surf. Coat. Technol. 83 (1996) 284–289. [15] A.A. Youssef, P. Budzynski, J. Filiks, Z. Surowiec, Improvement of tribological properties of aluminum by nitrogen implantation, Vacuum 78 (2005) 599–603. [16] R.J. Rodriguez, A. Sanz, A. Medrano, J. Garcia-Lorente, Tribological properties of ion implanted aluminum alloys, Vacuum 52 (1999) 187–192. [17] K.C. Walter, R.A. Dodd, J.R. Conrad, Corrosion behavior of nitrogen implanted aluminum, Nucl. Instrum. Methods Phys. Res., Sect. B: Beam Interact. Mater. and At. 106 (1995) 522–526. [18] S. Seghrouchni, Caractérisation chimique et structurale de revêtements d’aluminium oxydé et nitruré et étude de leur réactivité électrochimique en milieux acide et chloruré, in: Ph.D., Université Louis Pasteur, Strasbourg, 1996. [19] J.M. Williams, A. Gonzales, J. Quintana, I.S. Lee, R.A. Buchanan, F.C. Burns, R.J. Culbertson, M. Levy, J.R. Treglio, Ion implantation for corrosion inhibition of aluminum alloys in saline media, Nucl. Instrum. Methods Phys. Res., Sect. B: Beam Interact. Mater. and At. 59–60 Part 2 (1991) 845–850. [20] Y. Massiani, J.P. Crousier, L. Fedrizzi, S. Gialanella, P.L. Bonora, Electrochemical study of multiple-energy nitrogen-ion-implanted aluminium alloys, Mater. Sci. Eng., A 116 (1989) 53–57. [21] E. Hug, S. Thibault, D. Chateigner, L. Maunoury, Nitriding aluminum alloys by N-multicharged ions implantation: correlation between surface strengthening and microstructure modifications, Surf. Coat. Technol. 206 (2012) 5028–5035. [22] J.F. Ziegler, M.D. Ziegler, J.P. Biersack, SRIM: the stopping and range of ions in matter, Nucl. Instrum. Methods Phys. Res., Sect. B: Beam Interact. Mater. and At. 268 (2010) 1818–1823. [23] C. Vargel, Corrosion de l’aluminium, Dunod, Paris, 1999. [24] B.B. Wang, Z.Y. Wang, W. Han, W. Ke, Atmospheric corrosion of aluminium alloy 2024-T3 exposed to salt lake environment in Western China, Corros. Sci. 59 (2012) 63–70. [25] M. Stern, A.L. Geary, Electrochemical polarization. 1: A theoretical analysis of the shape of polarization curves, J. Electrochem. Soc. 104 (1957) 56–63. [26] U. Trdan, J. Grum, Evaluation of corrosion resistance of AA6082-T651 aluminium alloy after laser shock peening by means of cyclic polarisation and ElS methods, Corros. Sci. 59 (2012) 324–333. [27] H. Ezuber, A. El-Houd, F. El-Shawesh, A study on the corrosion behavior of aluminum alloys in seawater, Mater. Des. 29 (2008) 801–805.
Please cite this article in press as: S. Thibault, E. Hug, Corrosion and wear mechanisms of aluminum alloys surface reinforced by multicharged N-implantation, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.03.164