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Corrosion and oxidation behavior of amorphous and nanoquasicrystalline phases in Zr70Pd30 and Zr80Pt20 alloys
Journal of Non-Crystalline Solids 334&335 (2004) 544–547 www.elsevier.com/locate/jnoncrysol
Corrosion and oxidation behavior of amorphous and nanoquasicrystalline phases in Zr70Pd30 and Zr80Pt20 alloys K. Mondal, U.K. Chatterjee, B.S. Murty
*
Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Materials Engineering, Kharagpur 721 302, India
Abstract The corrosion behavior of melt-spun amorphous and nanoquasicrystalline Zr80 Pt20 ribbons and amorphous Zr70 Pd30 ribbons has been investigated using a potentiodynamic polarization study in a neutral NaCl solution. All three alloys are susceptible to chloride attack, and pitting is observed. The pitting corrosion behavior of these alloys has been compared with zirconium (98% pure). The oxidation behavior of the amorphous Zr70 Pd30 alloy and the partially nanocrystalline Zr80 Pt20 alloys has been studied non-isothermally by a thermo-gravimetric analysis in static air at different heating rates up to 773 K. It was observed that the amorphous Zr70 Pd30 alloy readily oxidizes. Zr80 Pt20 alloys in the nanoquasicrystalline state are more resistant to oxidation. Ó 2004 Elsevier B.V. All rights reserved. PACS: 82.45.Bb; 81.65.Mq; 61.43.Dq; 61.82.Rx; 76.30.He
1. Introduction Since the synthesis of the amorphous phase in the Au–Si system by the rapid solidification technique in 1959 [1], a great number of amorphous alloys have been developed over the past three decades. Recently, Murty et al. [2] have found that in binary Zr–Pd and Zr–Pt alloys, near their eutectic composition, amorphization is possible by rapid quenching and that these alloys lead to nanoquasicrystallization. One important aspect in the search for potential applications of the newly developed amorphous and nanocrystalline alloys is their stability under different environmental conditions, which will in turn decide their long time functionality [3]. Corrosion investigations on many multicomponent glass forming Zr-based amorphous alloys have been carried out in different corrosive media [4,5]. But, much less attention has been directed toward corrosion studies of simple binary Zr-based amorphous alloys. Dey et al. [6] tried to carry out an aqueous corrosion investigation on amorphous and crystalline Zr–Ni alloys in different acid media. The corrosion behavior of the amorphous Zr–Cu alloy was compared with that of its crystalline *
Corresponding author. Tel.: +91-3222 283 270; fax: +91-3222 282 280/55303. E-mail address: [email protected] (B.S. Murty). 0022-3093/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2003.12.038
counterpart by Naka et al. [5]. In the present study, the corrosion behavior of melt-spun Zr80 Pt20 and Zr70 Pd30 alloys was investigated in different environments. For high temperature applications, the oxidation behavior of amorphous as well as nanocrystalline alloys needs to be understood. Recent studies [7,8] have cited a high sensitivity of some of these alloys to oxidation. Depending on the alloying elements, such alloys exhibit either excellent or rather poor oxidation properties [9,10]. K€ oster et al. [7,8] carried out isothermal studies of the oxidation behavior of some Zr-based multicomponent amorphous alloys and concluded that the oxide layer consists of mainly ZrO2 , and that the oxidation resistance could be improved either by reducing the driving force or the mobility of the rate controlling element. In the present investigation, the non-isothermal oxidation behavior of binary melt-spun and heat treated Zr70 Pd30 and Zr80 Pt20 alloys was studied.
2. Experimental details The arc melted alloys were rapidly solidified by melt spinning at wheel speed of 20 and 40 m/s for Zr80 Pt20 and at 20 m/s for Zr70 Pd30 . The alloys were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) and scanning electron
K. Mondal et al. / Journal of Non-Crystalline Solids 334&335 (2004) 544–547
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microscopy (SEM). The corrosion characteristics of the alloys were determined based on the registration of anodic polarization curves obtained using the potentiodynamic method. The potentiodynamic polarization was carried out using a three-electrode principle, where platinum was used as the counter electrode and a saturated calomel electrode was used as the reference electrode in a PS6 Mainsberger potentiostat/galvanostat. The samples were tested in 0.5 N NaCl at room temperature. All potentials were measured against the saturated calomel electrode and the potential of the tested samples was changed at a rate of 0.5 mV/s. Non-isothermal thermogravimetry was carried out in static air up to 773 K at four different heating rates (2.5, 5, 10 and 20 K/min). Fig. 1. XRD patterns of Zr70 Pd30 -20 m/s and Zr80 Pt20 alloys (20 and 40 m/s) in the melt-spun condition.
3. Results and discussion Fig. 1 shows the XRD patterns of the melt-spun Zr70 Pd30 and Zr80 Pt20 alloys. The Zr70 Pd30 alloy is
Fig. 2. HREM image of Zr70 Pd30 -20 m/s in the melt-spun condition. Fig. 4. SEM photomicrograph of the corroded surface of Zr70 Pd30 -20 m/s in NaCl showing chloride pitting.
Fig. 3. Dynamic polarization curves of all the melt-spun alloys in a 0.5 N NaCl solution.
Fig. 5. Variation of weight gain/unit area with temperature for all of the melt-spun alloys in static air at a heating rate of 2.5 K/min.
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Fig. 7. XRD patterns of the surface oxides of Zr70 Pd30 -20 m/s and (b) Zr80 Pt20 -40 m/s at the heating rate of 5 K/min.
Fig. 6. SEM microphotographs of oxidized surfaces: (a) Zr70 Pd30 -20 m/s at 20 K/min, (b) Zr80 Pt20 -20 m/s at 5 K/min and (b) Zr80 Pt20 -40 m/ s at 5 K/min.
completely amorphous and the amorphous structure is clearly visible in the high-resolution electron micrograph (Fig. 2). However, a number of clusters with short range order are evident from the high resolution micrograph. The other two alloys (Zr80 Pt20 -20 m/s and 40 m/s) are partially nanoquasicrystallized during rapid solidification and the Zr80 Pt20 -40 m/s alloy contains a larger volume fraction of the amorphous phase. The nanocrystalline phase has been indexed as the icosahedral phase. The nature of the polarization curves in 0.5 N NaCl of all the melt-spun alloys is shown in Fig. 3. In all cases, the melt-spun alloys have shown active–passive transi-
tion and sudden break-down in their polarization curves. Zr80 Pt20 alloys have the highest break-down potential (EBR ) in comparison to the Zr70 Pd30 -20m/s alloy. The presence of the more noble metal platinum could be the reason for their high pitting resistance. This could also be attributed to the nanoquasicrystalline phase present in these alloys. Zr80 Pt20 -20m/s has the highest pitting resistance as its EBR is the highest. The more strained structure of Zr80 Pt20 -40 m/s led to accelerated pitting in comparison to Zr80 Pt20 , made at a lower melt spinning rate. Fig. 4 shows the evidence of pitting in the melt-spun Zr70 Pd30 -20 m/s in a 0.5 N NaCl solution. These alloys have a higher pitting corrosion resistance in comparison to crystalline Zr, which has a lower EBR , a more negative open circuit potential, and a higher passive current density. Fig. 5 shows the variation of weight gain per unit area of the samples of all the melt-spun alloys for a heating rate of 2.5 K/min. This clearly indicates that Zr70 Pd30 -20 m/s is the most oxidation prone alloy among all of the three as melt-spun alloys. The same trend was observed for other heating rates. The oxidation resistance of the nanoquasicrystalline Zr80 Pt20 alloys is better than that
K. Mondal et al. / Journal of Non-Crystalline Solids 334&335 (2004) 544–547
of the amorphous Zr70 Pd30 -20 m/s alloy. The Zr80 Pt20 40 m/s alloy has a greater oxidation tendency than Zr80 Pt20 -20 m/s, because the volume fraction of the amorphous phase is greater in Zr80 Pt20 -40 m/s. The more open structure of the glass appears to facilitate a higher degree of oxygen diffusion into the alloy, leading to a greater oxidation tendency. The oxidation process in these alloy systems follows parabolic oxidation kinetics. The surface morphologies of these alloys after oxidation are shown in Fig. 6(a)–(c). Zr70 Pd30 -20 m/s in the melt-spun condition shows wide cracks and a swelling of the surface oxidized layer (Fig. 6(a)), whereas in the other two cases (Zr80 Pt20 alloys) the cracks are very fine (Fig. 6(b) and (c)). XRD of the surface oxide (Fig. 7(a) and (b)) has shown that the main oxide formed is ZrO2 in both the systems. Two other oxides are PdO and PtO2 , which form in Zr70 Pd30 and Zr80 Pt20 , respectively. After oxidation Zr70 Pd30 -20 m/s became powder and only at the heating rate of 20 K/min, did it retain its shape after oxidation; but the two Pt-containing alloys retained their shape even at lower heating rates (5 K/min).
4. Conclusions Zr70 Pd30 -20 m/s is completely amorphous in the as melt-spun condition. Zr80 Pt20 alloys are partially nanoquasicrystalline in the as melt-spun state and Zr80 Pt20 -40
547
m/s has a higher volume fraction of the amorphous phase than that of Zr80 Pt20 -20 m/s. All of the alloys have shown pitting in a NaCl solution; the pitting corrosion resistance of the Pt-containing alloys is better than that of the Pd-containing alloy. The oxidation resistance of Zr70 Pd30 is minimum, presumably due to a more open structure of the amorphous phase in this alloy. With increase in nanocrystallinity, the oxidation resistance increases in the case of Zr80 Pt20 alloys. The oxide scale consists of mainly ZrO2 .
References [1] W. Klement, R.H. Willens, P. Duwez, Nature 187 (1960) 869. [2] B.S. Murty, D.H. Ping, M. Ohnuma, K. Hono, Acta Mater. 49 (2001) 3453. [3] A. Inoue, Acta Mater. 48 (2000) 277. [4] K. Hashimoto, K. Asami, K. Teramoto, Corros. Sci. 19 (1979) 3. [5] M. Naka, K. Hashimoto, T. Masumoto, J. Non-Cryst. Solids 28 (1987) 403. [6] G.K. Dey, R.T. Savalia, S.K. Sharma, S.K. Kulkarni, Corros. Sci. 29 (1989) 823. [7] Triwikantoro, D. Toma, M. Meuris, U. Koester, J. Non-Cryst. Solids 250–252 (1999) 719. [8] U. Koester, D. Zander, Triwikantoro, Mater. Sci. Forum 343– 346 (2000) 203. [9] A. Dhawan, K. Raetzke, F. Faupel, S.K. Sharma, Bull. Mater. Sci. 24 (2001) 281. [10] X. Sun, S. Schneider, U. Geyer, M.A. Nicolet, W.L. Jhonson, J. Mater. Res. 11 (1996) 2738.
Corrosion and oxidation behavior of amorphous and nanoquasicrystalline phases in Zr70Pd30 and Zr80Pt20 alloys K. Mondal, U.K. Chatterjee, B.S. Murty
*
Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Materials Engineering, Kharagpur 721 302, India
Abstract The corrosion behavior of melt-spun amorphous and nanoquasicrystalline Zr80 Pt20 ribbons and amorphous Zr70 Pd30 ribbons has been investigated using a potentiodynamic polarization study in a neutral NaCl solution. All three alloys are susceptible to chloride attack, and pitting is observed. The pitting corrosion behavior of these alloys has been compared with zirconium (98% pure). The oxidation behavior of the amorphous Zr70 Pd30 alloy and the partially nanocrystalline Zr80 Pt20 alloys has been studied non-isothermally by a thermo-gravimetric analysis in static air at different heating rates up to 773 K. It was observed that the amorphous Zr70 Pd30 alloy readily oxidizes. Zr80 Pt20 alloys in the nanoquasicrystalline state are more resistant to oxidation. Ó 2004 Elsevier B.V. All rights reserved. PACS: 82.45.Bb; 81.65.Mq; 61.43.Dq; 61.82.Rx; 76.30.He
1. Introduction Since the synthesis of the amorphous phase in the Au–Si system by the rapid solidification technique in 1959 [1], a great number of amorphous alloys have been developed over the past three decades. Recently, Murty et al. [2] have found that in binary Zr–Pd and Zr–Pt alloys, near their eutectic composition, amorphization is possible by rapid quenching and that these alloys lead to nanoquasicrystallization. One important aspect in the search for potential applications of the newly developed amorphous and nanocrystalline alloys is their stability under different environmental conditions, which will in turn decide their long time functionality [3]. Corrosion investigations on many multicomponent glass forming Zr-based amorphous alloys have been carried out in different corrosive media [4,5]. But, much less attention has been directed toward corrosion studies of simple binary Zr-based amorphous alloys. Dey et al. [6] tried to carry out an aqueous corrosion investigation on amorphous and crystalline Zr–Ni alloys in different acid media. The corrosion behavior of the amorphous Zr–Cu alloy was compared with that of its crystalline *
Corresponding author. Tel.: +91-3222 283 270; fax: +91-3222 282 280/55303. E-mail address: [email protected] (B.S. Murty). 0022-3093/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2003.12.038
counterpart by Naka et al. [5]. In the present study, the corrosion behavior of melt-spun Zr80 Pt20 and Zr70 Pd30 alloys was investigated in different environments. For high temperature applications, the oxidation behavior of amorphous as well as nanocrystalline alloys needs to be understood. Recent studies [7,8] have cited a high sensitivity of some of these alloys to oxidation. Depending on the alloying elements, such alloys exhibit either excellent or rather poor oxidation properties [9,10]. K€ oster et al. [7,8] carried out isothermal studies of the oxidation behavior of some Zr-based multicomponent amorphous alloys and concluded that the oxide layer consists of mainly ZrO2 , and that the oxidation resistance could be improved either by reducing the driving force or the mobility of the rate controlling element. In the present investigation, the non-isothermal oxidation behavior of binary melt-spun and heat treated Zr70 Pd30 and Zr80 Pt20 alloys was studied.
2. Experimental details The arc melted alloys were rapidly solidified by melt spinning at wheel speed of 20 and 40 m/s for Zr80 Pt20 and at 20 m/s for Zr70 Pd30 . The alloys were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) and scanning electron
K. Mondal et al. / Journal of Non-Crystalline Solids 334&335 (2004) 544–547
545
microscopy (SEM). The corrosion characteristics of the alloys were determined based on the registration of anodic polarization curves obtained using the potentiodynamic method. The potentiodynamic polarization was carried out using a three-electrode principle, where platinum was used as the counter electrode and a saturated calomel electrode was used as the reference electrode in a PS6 Mainsberger potentiostat/galvanostat. The samples were tested in 0.5 N NaCl at room temperature. All potentials were measured against the saturated calomel electrode and the potential of the tested samples was changed at a rate of 0.5 mV/s. Non-isothermal thermogravimetry was carried out in static air up to 773 K at four different heating rates (2.5, 5, 10 and 20 K/min). Fig. 1. XRD patterns of Zr70 Pd30 -20 m/s and Zr80 Pt20 alloys (20 and 40 m/s) in the melt-spun condition.
3. Results and discussion Fig. 1 shows the XRD patterns of the melt-spun Zr70 Pd30 and Zr80 Pt20 alloys. The Zr70 Pd30 alloy is
Fig. 2. HREM image of Zr70 Pd30 -20 m/s in the melt-spun condition. Fig. 4. SEM photomicrograph of the corroded surface of Zr70 Pd30 -20 m/s in NaCl showing chloride pitting.
Fig. 3. Dynamic polarization curves of all the melt-spun alloys in a 0.5 N NaCl solution.
Fig. 5. Variation of weight gain/unit area with temperature for all of the melt-spun alloys in static air at a heating rate of 2.5 K/min.
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Fig. 7. XRD patterns of the surface oxides of Zr70 Pd30 -20 m/s and (b) Zr80 Pt20 -40 m/s at the heating rate of 5 K/min.
Fig. 6. SEM microphotographs of oxidized surfaces: (a) Zr70 Pd30 -20 m/s at 20 K/min, (b) Zr80 Pt20 -20 m/s at 5 K/min and (b) Zr80 Pt20 -40 m/ s at 5 K/min.
completely amorphous and the amorphous structure is clearly visible in the high-resolution electron micrograph (Fig. 2). However, a number of clusters with short range order are evident from the high resolution micrograph. The other two alloys (Zr80 Pt20 -20 m/s and 40 m/s) are partially nanoquasicrystallized during rapid solidification and the Zr80 Pt20 -40 m/s alloy contains a larger volume fraction of the amorphous phase. The nanocrystalline phase has been indexed as the icosahedral phase. The nature of the polarization curves in 0.5 N NaCl of all the melt-spun alloys is shown in Fig. 3. In all cases, the melt-spun alloys have shown active–passive transi-
tion and sudden break-down in their polarization curves. Zr80 Pt20 alloys have the highest break-down potential (EBR ) in comparison to the Zr70 Pd30 -20m/s alloy. The presence of the more noble metal platinum could be the reason for their high pitting resistance. This could also be attributed to the nanoquasicrystalline phase present in these alloys. Zr80 Pt20 -20m/s has the highest pitting resistance as its EBR is the highest. The more strained structure of Zr80 Pt20 -40 m/s led to accelerated pitting in comparison to Zr80 Pt20 , made at a lower melt spinning rate. Fig. 4 shows the evidence of pitting in the melt-spun Zr70 Pd30 -20 m/s in a 0.5 N NaCl solution. These alloys have a higher pitting corrosion resistance in comparison to crystalline Zr, which has a lower EBR , a more negative open circuit potential, and a higher passive current density. Fig. 5 shows the variation of weight gain per unit area of the samples of all the melt-spun alloys for a heating rate of 2.5 K/min. This clearly indicates that Zr70 Pd30 -20 m/s is the most oxidation prone alloy among all of the three as melt-spun alloys. The same trend was observed for other heating rates. The oxidation resistance of the nanoquasicrystalline Zr80 Pt20 alloys is better than that
K. Mondal et al. / Journal of Non-Crystalline Solids 334&335 (2004) 544–547
of the amorphous Zr70 Pd30 -20 m/s alloy. The Zr80 Pt20 40 m/s alloy has a greater oxidation tendency than Zr80 Pt20 -20 m/s, because the volume fraction of the amorphous phase is greater in Zr80 Pt20 -40 m/s. The more open structure of the glass appears to facilitate a higher degree of oxygen diffusion into the alloy, leading to a greater oxidation tendency. The oxidation process in these alloy systems follows parabolic oxidation kinetics. The surface morphologies of these alloys after oxidation are shown in Fig. 6(a)–(c). Zr70 Pd30 -20 m/s in the melt-spun condition shows wide cracks and a swelling of the surface oxidized layer (Fig. 6(a)), whereas in the other two cases (Zr80 Pt20 alloys) the cracks are very fine (Fig. 6(b) and (c)). XRD of the surface oxide (Fig. 7(a) and (b)) has shown that the main oxide formed is ZrO2 in both the systems. Two other oxides are PdO and PtO2 , which form in Zr70 Pd30 and Zr80 Pt20 , respectively. After oxidation Zr70 Pd30 -20 m/s became powder and only at the heating rate of 20 K/min, did it retain its shape after oxidation; but the two Pt-containing alloys retained their shape even at lower heating rates (5 K/min).
4. Conclusions Zr70 Pd30 -20 m/s is completely amorphous in the as melt-spun condition. Zr80 Pt20 alloys are partially nanoquasicrystalline in the as melt-spun state and Zr80 Pt20 -40
547
m/s has a higher volume fraction of the amorphous phase than that of Zr80 Pt20 -20 m/s. All of the alloys have shown pitting in a NaCl solution; the pitting corrosion resistance of the Pt-containing alloys is better than that of the Pd-containing alloy. The oxidation resistance of Zr70 Pd30 is minimum, presumably due to a more open structure of the amorphous phase in this alloy. With increase in nanocrystallinity, the oxidation resistance increases in the case of Zr80 Pt20 alloys. The oxide scale consists of mainly ZrO2 .
References [1] W. Klement, R.H. Willens, P. Duwez, Nature 187 (1960) 869. [2] B.S. Murty, D.H. Ping, M. Ohnuma, K. Hono, Acta Mater. 49 (2001) 3453. [3] A. Inoue, Acta Mater. 48 (2000) 277. [4] K. Hashimoto, K. Asami, K. Teramoto, Corros. Sci. 19 (1979) 3. [5] M. Naka, K. Hashimoto, T. Masumoto, J. Non-Cryst. Solids 28 (1987) 403. [6] G.K. Dey, R.T. Savalia, S.K. Sharma, S.K. Kulkarni, Corros. Sci. 29 (1989) 823. [7] Triwikantoro, D. Toma, M. Meuris, U. Koester, J. Non-Cryst. Solids 250–252 (1999) 719. [8] U. Koester, D. Zander, Triwikantoro, Mater. Sci. Forum 343– 346 (2000) 203. [9] A. Dhawan, K. Raetzke, F. Faupel, S.K. Sharma, Bull. Mater. Sci. 24 (2001) 281. [10] X. Sun, S. Schneider, U. Geyer, M.A. Nicolet, W.L. Jhonson, J. Mater. Res. 11 (1996) 2738.