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Potentiodynamic polarization studies on amorphous Zr46.75Ti8.25Cu7.5Ni10Be27.5, Zr65Cu17.5Ni10Al7.5, Zr67Ni33 and Ti60Ni40 in aqueous HNO3 solutions
Journal of Non-Crystalline Solids 353 (2007) 2619–2623 www.elsevier.com/locate/jnoncrysol
Potentiodynamic polarization studies on amorphous Zr46.75Ti8.25Cu7.5Ni10Be27.5, Zr65Cu17.5Ni10Al7.5, Zr67Ni33 and Ti60Ni40 in aqueous HNO3 solutions A. Dhawan
a,1 a
, K. Sachdev
a,*
, S. Roychowdhury b, P.K. De b, S.K. Sharma
a
Department of Physics, Malaviya National Institute of Technology, Jaipur 302 017, India Corrosion Science Section, Materials Science Division, BARC, Mumbai 400 085, India
b
Received 20 October 2006; received in revised form 29 April 2007 Available online 26 June 2007
Abstract Potentiodynamic polarization studies were carried out on virgin specimens of Zr-based bulk amorphous alloys Zr46.75Ti8.25Cu7.5Ni10Be27.5 and Zr65Cu17.5Ni10Al7.5, and conventional-type binary amorphous alloys Zr67Ni33 and Ti60Ni40 in solutions of 0.2 M, 0.5 M and 1.0 M HNO3 at room temperature. The values of the corrosion current density (Icorr) for the bulk amorphous alloy Zr46.75Ti8.25Cu7.5Ni10Be27.5 were found to be comparable with those of Zr65Cu17.5Ni10Al7.5 in 0.2 M and 0.5 M HNO3, but the value of Icorr for the former was almost three times more than that of the latter in 1.0 M HNO3. In the case of conventional binary amorphous alloys, Ti60Ni40 showed lower value of Icorr as compared to Zr67Ni33 in 0.5 M and 1.0 M HNO3 and a comparable value of Icorr in 0.2 M HNO3. In general, the binary Ti60Ni40 displayed the best corrosion resistance among all the alloys in all the cases and the corrosion current density (Icorr) for all the alloys was found to increase with the increasing concentration of nitric acid. It is noticed that the bulk amorphous alloys do not possess superior corrosion resistance as compared to conventional binary amorphous alloys in aqueous HNO3 solutions. The observed differences in their corrosion behavior are attributed to different alloy constituents and composition of the alloys investigated. 2007 Elsevier B.V. All rights reserved. PACS: 61.43.Dq; 81.65.Kn; 81.65.Mq; 64.70.Pf; 61.10.Nz Keywords: Alloys; Corrosion; Oxidation reduction; Glass transition; X-ray diffraction
1. Introduction Amorphous alloys, in general, exhibit superior mechanical and chemical properties vis-a`-vis their crystalline counterparts. Bulk amorphous alloys belong to a new class of amorphous materials which require very low cooling rates of about 1 K/s unlike conventional melt-spun amorphous alloys which need much higher cooling rates of about 105–106 K/s [1]. Zr-based alloys such as Zr65Cu17.5Ni10Al7.5 *
Corresponding author. Tel.: +91 141 2622497. E-mail address: [email protected] (K. Sachdev). 1 Present address: Department of Physics, Jagannath Gupta Institute of Engineering & Technology, Jaipur 302 022, India. 0022-3093/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2007.05.002
and Zr46.75Ti8.25Cu7.5Ni10Be27.5 (also known as Vitreloy-4 or V4) can be processed in bulk amorphous form and are of much interest in both research and several applications [2]. In addition, these are ideal materials for carrying out thermal studies above glass transition temperature because of their large supercooled liquid region, which extends up to about 100 K [3]. It is important to have the knowledge of thermo-chemical (oxidation/corrosion) properties of these alloys at room as well as elevated temperatures in view of their possible applications. Although there are several investigations on the corrosion behavior of conventional amorphous alloys (e.g. [4–7] and references therein), only a limited information is available in the literature on corrosion behavior of bulk amorphous alloys
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[8–15]. Schroeder et al. [8] investigated the corrosion behavior of Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk amorphous alloy with its crystalline counterpart in solutions of 0.5 M NaCl and 0.5 M NaClO4 at room temperature. According to the authors [8], amorphous structure is slightly more resistant to pitting corrosion than the corresponding crystalline structure in aqueous NaCl solution. Hiromoto et al. [9,10] studied the effect of chloride ions on the anodic polarization behavior and the effects of the surface finishing and dissolved oxygen on the polarization behavior of the amorphous Zr65Al7.5Ni10Cu17.5 in phosphate-buffered solution. It was reported in these studies that the susceptibility of this alloy to pitting corrosion was small at small concentration of chloride ions, but the same increased with the increase of concentration of chloride ions. Buchholz et al. [11] investigated the electrochemical behavior of Zr55Al10Cu30Ni5 bulk metallic glass. Their investigations indicated that in solutions of 0.01–0.1 M NaCl, pitting corrosion occurs in Zr55Al10Cu30Ni5 bulk metallic glass. Localized corrosion behavior of a bulk metallic glass Zr52.5Cu17.9Ni14.6Ti0.5Al10 relative to its crystalline state in NaCl and Na2SO4 solutions was investigated by Peter et al. [12]. It was reported by these authors that the amorphous material was more resistant to the on-set of pitting corrosion under natural corrosion conditions. Dutta et al. [13] investigated the corrosion behavior of rapidly solidified Zr76Ni16Fe8 alloy in chloride environment and found that the corrosion behavior of alloy Zr76Ni16Fe8 varies across its thickness in chloride environments. In another investigation Dutta et al. [14] have reported the effects of microcrystalline phases and quenched in defects on the corrosion of rapidly solidified Ti47Cu53 and Ti50Cu50 alloys in acidic chloride environments. In a recent investigation [15] the present authors reported their results on potentiodynamic polarization studies on bulk amorphous alloys Zr46.75Ti8.25Cu7.5Ni10Be27.5 and Zr65Cu17.5Ni10Al7.5 in 0.5 M solutions of H2SO4, HNO3, HCl and NaOH. It was shown that the alloy Zr46.75Ti8.25Cu7.5Ni10Be27.5 is more prone to corrosion than the alloy Zr65Cu17.5Ni10Al7.5. The majority of reported investigations on bulk amorphous alloys mainly pertain to their corrosion behavior in different aqueous solutions and a comparative study with conventional-type amorphous alloys under identical experimental conditions has not been undertaken in these investigations. The motivation for the present study was derived from the need for carrying out a comparative study of corrosion behavior of Zr- based bulk amorphous alloys and conventional-type amorphous alloys containing bulk alloy constituents in an oxidizing medium like HNO3 of varying concentration using polarization method. Based on potentiodynamic polarization studies, the present investigation examines the corrosion behavior of Zr46.75Ti8.25Cu7.5Ni10Be27.5 and Zr65Cu17.5Ni10Al7.5 bulk amorphous alloys, and conventional-type binary Zr67Ni33 and Ti60Ni40 amorphous alloys in an oxidizing acidic medium (HNO3) as a function of its concentration (0.2 M, 0.5 M and 1.0 M) at room temperature (300 K).
2. Experimental As-received specimens of Zr65Cu17.5Ni10Al7.5 (1.5 cm · 1 cm · 41 lm), Zr46.75Ti8.25Cu7.5Ni10Be27.5 (5.0 mm diameter · 0.45 mm thickness), Zr67Ni33 (1.65 cm · 0.2 cm · 20 lm) and Ti60Ni40 (1 cm · 1 cm · 30 lm) were polished with #600 and subsequently with #1000 SiC paper. The amorphous nature of the specimens was checked by X-ray diffraction. The bulk amorphous alloys Zr46.75Ti8.25Cu7.5Ni10Be27.5 and Zr65Cu17.5Ni10Al7.5 displayed a glass transition temperature (Tg) at 613 K and 645 K, respectively, in a DSC experiment at a heating rate of 20 K/ min, while the binary amorphous alloys Zr67Ni33 and Ti60Ni40 exhibited on-set crystallization temperature (Tx) at 701 K and 761 K, respectively at the same heating rate. Specimens were cleaned with acetone and ethanol and dried in air prior to inserting them in the corrosion cell for electrochemical studies. The specimens were joined with wire using silver paint so as to maintain good electrical contact during corrosion studies. The region of the sample, where silver paint was put, was covered with epoxy resin in order to prevent any reaction of silver paint with the solution during the electrochemical studies. Potentiodynamic polarization studies on these specimens were carried out using Potentiostat Echo Chemie (Model Auto Lab. 30) in solutions of 0.2 M, 0.5 M and 1.0 M HNO3 at room temperature (300 K). The solutions were deaerated with nitrogen gas before and during the electrochemical studies. A gas flow rate of 8.0 · 104 l s1 was maintained. The first conditioning of the working electrode was done by applying 1.0 V for 120 s in order to clean the surface of the specimen and then a time of 1.8 · 103 s was allowed for the stabilization of open circuit potential (OCP). This particular cathodic pre-treatment provided corrosion potential values with reasonably good reproducibility. In the second conditioning stage, the scanning of potential was done for both cathodic and anodic regions by applying end potentials in the polarization experiment. The end potentials were normally taken between 1000 mV and +1750 mV for scanning which was done with respect to OCP. The scanning rate was maintained as 1 mV/s during all measurements. A standard silver/silver chloride (Ag/AgCl) electrode was used as the reference electrode and platinum was used for the counter electrode. Reference electrode was separated from the cell solution by using a luggin capillary containing agar salt (KCl) bridge, the tip of which was kept quite close to the working electrode to minimize the iR drop. A fit to the experimental polarization curves (E versus I plots) was obtained using the following equation [16], which yielded the values of the corrosion current density (Icorr): I ¼ I corr fexp½s1 ðE Ecorr Þ exp½s2 ðE Ecorr Þg; where, s1 s2 Ecorr Icorr
slope of the anodic branch slope of the cathodic branch the corrosion potential corrosion current density in A/cm2
A. Dhawan et al. / Journal of Non-Crystalline Solids 353 (2007) 2619–2623 Polarization studies of Zr 65Cu17.5Ni10Al7.5 1.00
a
b
0.2 M HNO3 0.5 M HNO3 1.0 M HNO3
0.75
c
0.50 0.25
E[V]
The observed corrosion potential, i.e. the potential where I = 0, is taken as the corrosion potential Ecorr or the open circuit potential. A fit to the experimental polarization plots was performed using the software [General purpose electrochemical system software (GPES) for windows version 4.8] supplied by the maufacturer (Echo chemie B.V., Netherlands) according to the non-linear least square fit method with the values obtained from selected Tafel lines as starting parameters. After some iterations, a fit with the number of iterations and the goodness of fit parameter chi-square was obtained. The best fit was obtained for both the cathodic and the anodic regions of the polarization plot using this procedure, which yielded the values of Icorr and Ecorr. Prior to carrying out the polarization experiment, the above described experimental procedure employed for conditioning of the working electrode and for the stabilization of the OCP resulted in the maximum reproducibility of open circuit potential Ecorr and the corrosion current Icorr values. This was checked by taking several calibration runs under identical experimental conditions before starting the actual experiment. Based on these results a maximum scatter in the values of Ecorr and Icorr within ±5% and ±10%, respectively is estimated.
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0.00 -0.25 -0.50 -0.75 -1.00 -8
-7
10
-6
10
-5
10
-4
10
10
-3
-2
10
10
-1
10
2
I [A/cm ] Fig. 1. Potentiodynamic polarization plots of amorphous alloy Zr65Cu17.5Ni10Al7.5 in (a) 0.2 M HNO3; (b) 0.5 M HNO3; and (c) 1.0 M HNO3.
Polarization studies of Zr46.75Ti8.25Cu7.5Ni10Be27.5 (Vitreloy-4) 2.0 0.2 M HNO3 0.5 M HNO3 1.0 M HNO3
1.5
3. Results
a
c b
E[V]
1.0
The potentiodynamic polarization plots representing both the cathodic and anodic regions for Zr65Cu17.5Ni10Al7.5 and Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk amorphous alloys, are shown in Figs. 1, and 2, respectively. The values of the corrosion current density (Icorr) and the open circuit potential (Ecorr) obtained from these plots are mentioned in Table 1. It is observed from Table 1 that the values of Icorr is maximum in 1.0 M HNO3 and minimum in 0.2 M HNO3 for both the alloys. A clear trend for passivity is seen in the case of amorphous Zr46.75Ti8.25Cu7.5Ni10Be27.5 in 0.2 M HNO3 (Fig. 2(a)), while in all other cases a passivity trend close to the open circuit potential is also noticeable (Figs. 1 and 2). Figs. 3 and 4 depict the polarization plots for conventional binary Zr67Ni33 and Ti60Ni40 amorphous alloys, respectively. A trend for passive-like behavior from the OCP is noticeable for Ti60Ni40 in all concentrations of HNO3 solutions and for Zr67Ni33 in 0.2 M HNO3. It is observed from Table 1 that the trend for Icorr for binary
0.5
0.0
-0.5
-1.0 -6
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
10
2
I [A/cm ] Fig. 2. Potentiodynamic polarization plots of amorphous alloy Zr46.75Ti8.25Cu7.5Ni10Be27.5 in (a) 0.2 M HNO3; (b) 0.5 M HNO3; and (c) 1.0 M HNO3.
alloys is same as found for the bulk alloys. The variation in Icorr for different alloys as a function of concentration of nitric acid is plotted in Fig. 5. It is seen from this figure that the Icorr values for all the amorphous alloys increase with an increase in the concentration of nitric acid. The
Table 1 Electrochemical response of amorphous Zr65Cu17.5Ni10Al7.5, Zr46.75Ti8.25Cu7.5Ni10Be27.5, Zr67Ni33 and Ti60Ni40 alloys in different concentrations of aqueous HNO3 solution Alloy designation
Zr65Cu17.5Ni10Al7.5 Zr46.75Ti8.25Cu7.5Ni10Be27.5 Zr67Ni33 Ti60Ni40
0.2 M HNO3
0.5 M HNO3
1.0 M HNO3
Ecorr (V)
Icorr (A/cm2)
Ecorr (V)
Icorr (A/cm2)
Ecorr (V)
Icorr (A/cm2)
0.06 0.09 0.14 0.12
3.5 · 106 3.9 · 106 5.0 · 107 5.2 · 107
0.03 0.03 0.07 0.11
4.0 · 106 5.5 · 106 4.3 · 106 1.3 · 106
0.04 0.08 0.03 0.10
1.8 · 105 5.0 · 105 1.2 · 105 4.2 · 106
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A. Dhawan et al. / Journal of Non-Crystalline Solids 353 (2007) 2619–2623 Polarization studies of Zr 67Ni33
Plot of Icorr vs Concentration -4
10
2.0
Zr65Cu17.5Ni10Al7.5 Zr46.75Ti8.25Cu7.5Ni10Be27.5 Zr67Ni33 Ti60Ni40
0.2 M HNO3 0.5 M HNO3 1.0 M HNO3
1.5
a
1.0
b
Icorr [A/cm ]
2
E[V]
c 0.5 0.0
-5
10
-0.5 -1.0 -6
10
-1.5 -9
10
-8
-7
10
10
-6
10
-5
-4
10
-3
10
10
-2
-1
10
10
2
I [A/cm ]
0.2
Fig. 3. Potentiodynamic polarization plots of amorphous alloy Zr67Ni33 in (a) 0.2 M HNO3; (b) 0.5 M HNO3; and (c) 1.0 M HNO3.
Polarization studies of Ti60Ni40
0.2 M HNO3 0.5 M HNO3 1.0 M HNO3
b
E[V]
c
0.5
0.0
-0.5
-1.0 -8
10
-7
10
-6
10
0.8
1.0
Fig. 5. Variation of corrosion current density (Icorr) for all the amorphous alloys versus concentration of HNO3.
4. Discussion a
1.0
0.6
1.0 M HNO3 solutions while its value in 0.2 M HNO3 is comparable to that of the other binary alloy Zr67Ni33.
2.0
1.5
0.4
Concentration of HNO3 (M)
-5
10
-4
10
-3
10
2
I [A/cm ] Fig. 4. Potentiodynamic polarization plots of amorphous alloy Ti60Ni40 in (a) 0.2 M HNO3; (b) 0.5 M HNO3; and (c) 1.0 M HNO3.
bulk amorphous alloy Zr46.75Ti8.25Cu7.5Ni10Be27.5 displays the highest value of Icorr followed by the other bulk amorphous alloy Zr65Cu17.5Ni10Al7.5, the binary amorphous alloys Zr67Ni33 and Ti60Ni40. Our results suggest that Zrbased bulk amorphous alloys do not seem to possess superior corrosion resistance vis-a`-vis conventional-type Zrand Ti-based amorphous alloys. On the contrary the bulk amorphous alloy Zr46.75Ti8.25Cu7.5Ni10Be27.5 is most prone to corrosion in comparison to the other amorphous alloys (Table 1 and Fig. 5) while the corrosion resistance of the other bulk alloy Zr65Cu17.5Ni10Al7.5 is also poorer than that of the binary alloys. The value of Icorr for the binary Zr67Ni33 in 0.2 M HNO3 is lower than that for the bulk amorphous alloy Zr65Cu17.5Ni10Al7.5 by about an order of magnitude, but in higher concentrations the Icorr values for both the alloys are comparable. The binary amorphous Ti60Ni40 exhibits the lowest value of Icorr in 0.5 M and
It is possible to understand the corrosion behavior of investigated alloys in HNO3 in terms of the differences in the nature of the anodic oxide films formed on surfaces of these alloys as reported in the literature [7,10,11,17– 22]. The anodic oxide films on amorphous Zr67Ni33 in 1 N HCl, 1 N HNO3 and 1 N H2SO4 [7] and on amorphous Ti50Cu50 [17] have been shown to consist of ZrO2/Zr(OH)2 and TiO2, respectively. On the other hand it has been reported that the anodic oxide film formed on the bulk amorphous alloy Zr65Cu17.5Ni10Al7.5 in phosphate-buffered solution [10] and on Zr55Al10Cu30Ni5 in 0.1 M Na2SO4 [11,18] are complex oxide films consisting of ZrO2 as major oxide in addition to the other alloying elements Al, Cu and Ni. It was shown by Gebert et al. [18] that the complex anodic oxide film formed on amorphous Zr55Al10Cu30Ni5 in 0.1 M Na2SO4 has poor protective quality than the film formed on pure Zr in the same aqueous medium. It is further noteworthy here that native oxide films formed on Zr-based multicomponent Zr65Cu17.5Ni10Al7.5 and Zr46.75Ti8.25Cu7.5Ni10Be27.5 [19] have also been found to be complex in nature consisting of oxides of several alloy constituents in contrast to those formed on binary Zr67Ni33 [20] and Ti60Ni40 [21] amorphous alloys. In this connection it is seen from Table 1 that the open circuit potential Ecorr for bulk amorphous alloys are nobler than those for the binary alloys, thus suggesting the presence of other alloying elements like Cu, Ni, Al or Be during anodic film formation on the multicomponent bulk amorphous alloys. Similar observations have been made by Hiromoto et al. [10] during corrosion studies on amorphous Zr65Cu17.5Ni10Al7.5 in phosphate-buffered
A. Dhawan et al. / Journal of Non-Crystalline Solids 353 (2007) 2619–2623
solution and the shift of the OCP towards the nobler side has been attributed to the presence of Cu and Ni in the surface oxide film. The possible explanation for the lowest value of Icorr in the case of amorphous Ti60Ni40 alloy as compared to the binary and the bulk amorphous alloys could be attributed to the formation of a strong and protective film of TiO2 on the alloy surface. The formation of a strong passive film of TiO2 during the anodic polarization of the Ti60Ni40 alloy is also suggested by the observed large passivity regions as shown in Fig. 4. It has been further reported that oxide film formed on Ti-based amorphous alloys are more rigid compared to those formed on Zr-based alloys and it has been attributed to the greater affinity of Ti for oxygen atoms [22]. From the above discussion it may be mentioned in regard to the investigations reported here that the anodic oxide films formed on binary alloys Zr67Ni33 and Ti60Ni40 are likely to be more homogeneous and uniform with a better protective quality than the complex oxide films formed on multicomponent bulk amorphous alloys Zr65Cu17.5Ni10Al7.5 and Zr46.75Ti8.25Cu7.5Ni10Be27.5. It is thus suggested from the above discussion that the bulk amorphous alloys Zr65Cu17.5Ni10Al7.5 and Zr46.75Ti8.25Cu7.5Ni10Be27.5 are not superior to binary conventional-type amorphous alloys Zr67Ni33 and Ti60Ni40 so far as their corrosion resistance in aqueous HNO3 is concerned. In contrast, bulk alloy Zr46.75Ti8.25Cu7.5Ni10Be27.5 seems to be more prone to corrosion in comparison to the other alloys and the conventional-type binary amorphous alloy Ti60Ni40 displays the maximum resistance to corrosion in aqueous HNO3 solution. 5. Conclusions i) The corrosion current density was found to be maximum for the bulk amorphous alloy Zr46.75Ti8.25Cu7.5Ni10Be27.5 followed by that for the other bulk amorphous alloy Zr65Cu17.5Ni10Al7.5 and binary alloys Zr67Ni33, Ti60Ni40 in 0.2 M, 0.5 M and 1.0 M HNO3 aqueous solutions. ii) It is suggested that the bulk amorphous alloys Zr65Cu17.5Ni10Al7.5 and Zr46.75Ti8.25Cu7.5Ni10Be27.5 are not superior to conventional amorphous alloys Zr67Ni33 and Ti60Ni40 so far as their corrosion behavior in aqueous HNO3 is concerned.
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Acknowledgements The Financial support for this work under DAE/BRNS Research Project (Grants No. 99/37/25/BRNS) is gratefully acknowledged. Thanks are due to Dr M.-P. Macht, HMI Berlin for giving us the amorphous alloy specimens for this work. References [1] T. Zhang, A. Inoue, T. Masumoto, Mater. Trans. JIM 32 (1991) 1005. [2] W.L. Johnson, Curr. Opin. Solid St. M. 1 (1996) 383. [3] A. Pecker, W.L. Johnson, Appl. Phys. Lett. 63 (1993) 2342. [4] M.W. Tan, E. Akiyama, A. Kawashima, K. Asami, K. Hasimoto, Corros. Sci. 38 (1996) 349. [5] K. Asami, M. Naka, K. Hasimoto, T. Masumoto, J. Electrochem. Soc. 127 (1980) 2130. [6] R.B. Diegle, Corrosion 35 (1979) 250. [7] G.K. Dey, R.T. Savalia, S.K. Sharma, S.K. Kulkarni, Corros. Sci. 29 (1989) 823. [8] V. Schroeder, C.J. Gilbert, R.O. Ritchie, Scr. Mater. 38 (1998) 1481. [9] S. Hiromoto, A.-P. Tsai, M. Sumita, T. Hanawa, Corros. Sci. 42 (2000) 1651. [10] S. Hiromoto, A.-P. Tsai, M. Sumita, T. Hanawa, Corros. Sci. 42 (2000) 2167. [11] K. Bulchholz, A. Gebert, K. Mummert, J. Eckert, L. Schultz, Mat. Res. Soc. Symp. Proc. 554 (1999) 161. [12] W.H. Peter, R.A. Buchanan, C.T. Liu, P.K. Liaw, M.L. Morrison, J.A. Horton, C.A. Carmichael Jr., J.L. Wright, Intermetallics 10 (2002) 1157. [13] R.S. Dutta, R.T. Savalia, G.K. Dey, Scr. Metall. Mater. 32 (1995) 207. [14] R.S. Dutta, R.T. Savalia, G.K. Dey, Brit. Corros. J. 36 (2001) 221. [15] A. Dhawan, S. Roychowdhury, P.K. De, S.K. Sharma, J. Non-Cryst. Solids 351 (2005) 951. [16] M. Stern, A.L. Geary, J. Electrochem. Soc. 104 (1957) 56. [17] R. Schennach, S. Promreuk, D.G. Naugle, D.L. Cocke, Oxid. Met. 55 (5/6) (2001) 523. [18] A. Gebert, K. Buchholz, A. Leonhard, K. Mummert, J. Eckert, L. Schultz, Mater. Sci. Eng. A 267 (1999) 294. [19] S.K. Sharma, T. Strunskus, H. Ladebusch, F. Faupel, Mater. Sci. Eng. A 304–306 (2001) 747. [20] D.L. Cocke, G. Liang, M. Owens, D.E. Halverson, D.G. Naugle, Mater. Sci. Eng. 99 (1988) 497. [21] P. Srivastava, S. Venkatesh, M. Khaled, K.B. Garg, S.K. Sharma, in: Proceedings of DAE Solid State Physics (SSP-94), University of Rajasthan, Jaipur, 27–31, December, 1994, p. 457. [22] Choll-Hong Hawang, Kangio Cho, Kazutaka Kawamura, Raipdly Quenched Metals, in: S. Steeb, H. Warlimont (Eds.), Elsevier Science, 1985, p. 1469.
Potentiodynamic polarization studies on amorphous Zr46.75Ti8.25Cu7.5Ni10Be27.5, Zr65Cu17.5Ni10Al7.5, Zr67Ni33 and Ti60Ni40 in aqueous HNO3 solutions A. Dhawan
a,1 a
, K. Sachdev
a,*
, S. Roychowdhury b, P.K. De b, S.K. Sharma
a
Department of Physics, Malaviya National Institute of Technology, Jaipur 302 017, India Corrosion Science Section, Materials Science Division, BARC, Mumbai 400 085, India
b
Received 20 October 2006; received in revised form 29 April 2007 Available online 26 June 2007
Abstract Potentiodynamic polarization studies were carried out on virgin specimens of Zr-based bulk amorphous alloys Zr46.75Ti8.25Cu7.5Ni10Be27.5 and Zr65Cu17.5Ni10Al7.5, and conventional-type binary amorphous alloys Zr67Ni33 and Ti60Ni40 in solutions of 0.2 M, 0.5 M and 1.0 M HNO3 at room temperature. The values of the corrosion current density (Icorr) for the bulk amorphous alloy Zr46.75Ti8.25Cu7.5Ni10Be27.5 were found to be comparable with those of Zr65Cu17.5Ni10Al7.5 in 0.2 M and 0.5 M HNO3, but the value of Icorr for the former was almost three times more than that of the latter in 1.0 M HNO3. In the case of conventional binary amorphous alloys, Ti60Ni40 showed lower value of Icorr as compared to Zr67Ni33 in 0.5 M and 1.0 M HNO3 and a comparable value of Icorr in 0.2 M HNO3. In general, the binary Ti60Ni40 displayed the best corrosion resistance among all the alloys in all the cases and the corrosion current density (Icorr) for all the alloys was found to increase with the increasing concentration of nitric acid. It is noticed that the bulk amorphous alloys do not possess superior corrosion resistance as compared to conventional binary amorphous alloys in aqueous HNO3 solutions. The observed differences in their corrosion behavior are attributed to different alloy constituents and composition of the alloys investigated. 2007 Elsevier B.V. All rights reserved. PACS: 61.43.Dq; 81.65.Kn; 81.65.Mq; 64.70.Pf; 61.10.Nz Keywords: Alloys; Corrosion; Oxidation reduction; Glass transition; X-ray diffraction
1. Introduction Amorphous alloys, in general, exhibit superior mechanical and chemical properties vis-a`-vis their crystalline counterparts. Bulk amorphous alloys belong to a new class of amorphous materials which require very low cooling rates of about 1 K/s unlike conventional melt-spun amorphous alloys which need much higher cooling rates of about 105–106 K/s [1]. Zr-based alloys such as Zr65Cu17.5Ni10Al7.5 *
Corresponding author. Tel.: +91 141 2622497. E-mail address: [email protected] (K. Sachdev). 1 Present address: Department of Physics, Jagannath Gupta Institute of Engineering & Technology, Jaipur 302 022, India. 0022-3093/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2007.05.002
and Zr46.75Ti8.25Cu7.5Ni10Be27.5 (also known as Vitreloy-4 or V4) can be processed in bulk amorphous form and are of much interest in both research and several applications [2]. In addition, these are ideal materials for carrying out thermal studies above glass transition temperature because of their large supercooled liquid region, which extends up to about 100 K [3]. It is important to have the knowledge of thermo-chemical (oxidation/corrosion) properties of these alloys at room as well as elevated temperatures in view of their possible applications. Although there are several investigations on the corrosion behavior of conventional amorphous alloys (e.g. [4–7] and references therein), only a limited information is available in the literature on corrosion behavior of bulk amorphous alloys
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[8–15]. Schroeder et al. [8] investigated the corrosion behavior of Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk amorphous alloy with its crystalline counterpart in solutions of 0.5 M NaCl and 0.5 M NaClO4 at room temperature. According to the authors [8], amorphous structure is slightly more resistant to pitting corrosion than the corresponding crystalline structure in aqueous NaCl solution. Hiromoto et al. [9,10] studied the effect of chloride ions on the anodic polarization behavior and the effects of the surface finishing and dissolved oxygen on the polarization behavior of the amorphous Zr65Al7.5Ni10Cu17.5 in phosphate-buffered solution. It was reported in these studies that the susceptibility of this alloy to pitting corrosion was small at small concentration of chloride ions, but the same increased with the increase of concentration of chloride ions. Buchholz et al. [11] investigated the electrochemical behavior of Zr55Al10Cu30Ni5 bulk metallic glass. Their investigations indicated that in solutions of 0.01–0.1 M NaCl, pitting corrosion occurs in Zr55Al10Cu30Ni5 bulk metallic glass. Localized corrosion behavior of a bulk metallic glass Zr52.5Cu17.9Ni14.6Ti0.5Al10 relative to its crystalline state in NaCl and Na2SO4 solutions was investigated by Peter et al. [12]. It was reported by these authors that the amorphous material was more resistant to the on-set of pitting corrosion under natural corrosion conditions. Dutta et al. [13] investigated the corrosion behavior of rapidly solidified Zr76Ni16Fe8 alloy in chloride environment and found that the corrosion behavior of alloy Zr76Ni16Fe8 varies across its thickness in chloride environments. In another investigation Dutta et al. [14] have reported the effects of microcrystalline phases and quenched in defects on the corrosion of rapidly solidified Ti47Cu53 and Ti50Cu50 alloys in acidic chloride environments. In a recent investigation [15] the present authors reported their results on potentiodynamic polarization studies on bulk amorphous alloys Zr46.75Ti8.25Cu7.5Ni10Be27.5 and Zr65Cu17.5Ni10Al7.5 in 0.5 M solutions of H2SO4, HNO3, HCl and NaOH. It was shown that the alloy Zr46.75Ti8.25Cu7.5Ni10Be27.5 is more prone to corrosion than the alloy Zr65Cu17.5Ni10Al7.5. The majority of reported investigations on bulk amorphous alloys mainly pertain to their corrosion behavior in different aqueous solutions and a comparative study with conventional-type amorphous alloys under identical experimental conditions has not been undertaken in these investigations. The motivation for the present study was derived from the need for carrying out a comparative study of corrosion behavior of Zr- based bulk amorphous alloys and conventional-type amorphous alloys containing bulk alloy constituents in an oxidizing medium like HNO3 of varying concentration using polarization method. Based on potentiodynamic polarization studies, the present investigation examines the corrosion behavior of Zr46.75Ti8.25Cu7.5Ni10Be27.5 and Zr65Cu17.5Ni10Al7.5 bulk amorphous alloys, and conventional-type binary Zr67Ni33 and Ti60Ni40 amorphous alloys in an oxidizing acidic medium (HNO3) as a function of its concentration (0.2 M, 0.5 M and 1.0 M) at room temperature (300 K).
2. Experimental As-received specimens of Zr65Cu17.5Ni10Al7.5 (1.5 cm · 1 cm · 41 lm), Zr46.75Ti8.25Cu7.5Ni10Be27.5 (5.0 mm diameter · 0.45 mm thickness), Zr67Ni33 (1.65 cm · 0.2 cm · 20 lm) and Ti60Ni40 (1 cm · 1 cm · 30 lm) were polished with #600 and subsequently with #1000 SiC paper. The amorphous nature of the specimens was checked by X-ray diffraction. The bulk amorphous alloys Zr46.75Ti8.25Cu7.5Ni10Be27.5 and Zr65Cu17.5Ni10Al7.5 displayed a glass transition temperature (Tg) at 613 K and 645 K, respectively, in a DSC experiment at a heating rate of 20 K/ min, while the binary amorphous alloys Zr67Ni33 and Ti60Ni40 exhibited on-set crystallization temperature (Tx) at 701 K and 761 K, respectively at the same heating rate. Specimens were cleaned with acetone and ethanol and dried in air prior to inserting them in the corrosion cell for electrochemical studies. The specimens were joined with wire using silver paint so as to maintain good electrical contact during corrosion studies. The region of the sample, where silver paint was put, was covered with epoxy resin in order to prevent any reaction of silver paint with the solution during the electrochemical studies. Potentiodynamic polarization studies on these specimens were carried out using Potentiostat Echo Chemie (Model Auto Lab. 30) in solutions of 0.2 M, 0.5 M and 1.0 M HNO3 at room temperature (300 K). The solutions were deaerated with nitrogen gas before and during the electrochemical studies. A gas flow rate of 8.0 · 104 l s1 was maintained. The first conditioning of the working electrode was done by applying 1.0 V for 120 s in order to clean the surface of the specimen and then a time of 1.8 · 103 s was allowed for the stabilization of open circuit potential (OCP). This particular cathodic pre-treatment provided corrosion potential values with reasonably good reproducibility. In the second conditioning stage, the scanning of potential was done for both cathodic and anodic regions by applying end potentials in the polarization experiment. The end potentials were normally taken between 1000 mV and +1750 mV for scanning which was done with respect to OCP. The scanning rate was maintained as 1 mV/s during all measurements. A standard silver/silver chloride (Ag/AgCl) electrode was used as the reference electrode and platinum was used for the counter electrode. Reference electrode was separated from the cell solution by using a luggin capillary containing agar salt (KCl) bridge, the tip of which was kept quite close to the working electrode to minimize the iR drop. A fit to the experimental polarization curves (E versus I plots) was obtained using the following equation [16], which yielded the values of the corrosion current density (Icorr): I ¼ I corr fexp½s1 ðE Ecorr Þ exp½s2 ðE Ecorr Þg; where, s1 s2 Ecorr Icorr
slope of the anodic branch slope of the cathodic branch the corrosion potential corrosion current density in A/cm2
A. Dhawan et al. / Journal of Non-Crystalline Solids 353 (2007) 2619–2623 Polarization studies of Zr 65Cu17.5Ni10Al7.5 1.00
a
b
0.2 M HNO3 0.5 M HNO3 1.0 M HNO3
0.75
c
0.50 0.25
E[V]
The observed corrosion potential, i.e. the potential where I = 0, is taken as the corrosion potential Ecorr or the open circuit potential. A fit to the experimental polarization plots was performed using the software [General purpose electrochemical system software (GPES) for windows version 4.8] supplied by the maufacturer (Echo chemie B.V., Netherlands) according to the non-linear least square fit method with the values obtained from selected Tafel lines as starting parameters. After some iterations, a fit with the number of iterations and the goodness of fit parameter chi-square was obtained. The best fit was obtained for both the cathodic and the anodic regions of the polarization plot using this procedure, which yielded the values of Icorr and Ecorr. Prior to carrying out the polarization experiment, the above described experimental procedure employed for conditioning of the working electrode and for the stabilization of the OCP resulted in the maximum reproducibility of open circuit potential Ecorr and the corrosion current Icorr values. This was checked by taking several calibration runs under identical experimental conditions before starting the actual experiment. Based on these results a maximum scatter in the values of Ecorr and Icorr within ±5% and ±10%, respectively is estimated.
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0.00 -0.25 -0.50 -0.75 -1.00 -8
-7
10
-6
10
-5
10
-4
10
10
-3
-2
10
10
-1
10
2
I [A/cm ] Fig. 1. Potentiodynamic polarization plots of amorphous alloy Zr65Cu17.5Ni10Al7.5 in (a) 0.2 M HNO3; (b) 0.5 M HNO3; and (c) 1.0 M HNO3.
Polarization studies of Zr46.75Ti8.25Cu7.5Ni10Be27.5 (Vitreloy-4) 2.0 0.2 M HNO3 0.5 M HNO3 1.0 M HNO3
1.5
3. Results
a
c b
E[V]
1.0
The potentiodynamic polarization plots representing both the cathodic and anodic regions for Zr65Cu17.5Ni10Al7.5 and Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk amorphous alloys, are shown in Figs. 1, and 2, respectively. The values of the corrosion current density (Icorr) and the open circuit potential (Ecorr) obtained from these plots are mentioned in Table 1. It is observed from Table 1 that the values of Icorr is maximum in 1.0 M HNO3 and minimum in 0.2 M HNO3 for both the alloys. A clear trend for passivity is seen in the case of amorphous Zr46.75Ti8.25Cu7.5Ni10Be27.5 in 0.2 M HNO3 (Fig. 2(a)), while in all other cases a passivity trend close to the open circuit potential is also noticeable (Figs. 1 and 2). Figs. 3 and 4 depict the polarization plots for conventional binary Zr67Ni33 and Ti60Ni40 amorphous alloys, respectively. A trend for passive-like behavior from the OCP is noticeable for Ti60Ni40 in all concentrations of HNO3 solutions and for Zr67Ni33 in 0.2 M HNO3. It is observed from Table 1 that the trend for Icorr for binary
0.5
0.0
-0.5
-1.0 -6
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
10
2
I [A/cm ] Fig. 2. Potentiodynamic polarization plots of amorphous alloy Zr46.75Ti8.25Cu7.5Ni10Be27.5 in (a) 0.2 M HNO3; (b) 0.5 M HNO3; and (c) 1.0 M HNO3.
alloys is same as found for the bulk alloys. The variation in Icorr for different alloys as a function of concentration of nitric acid is plotted in Fig. 5. It is seen from this figure that the Icorr values for all the amorphous alloys increase with an increase in the concentration of nitric acid. The
Table 1 Electrochemical response of amorphous Zr65Cu17.5Ni10Al7.5, Zr46.75Ti8.25Cu7.5Ni10Be27.5, Zr67Ni33 and Ti60Ni40 alloys in different concentrations of aqueous HNO3 solution Alloy designation
Zr65Cu17.5Ni10Al7.5 Zr46.75Ti8.25Cu7.5Ni10Be27.5 Zr67Ni33 Ti60Ni40
0.2 M HNO3
0.5 M HNO3
1.0 M HNO3
Ecorr (V)
Icorr (A/cm2)
Ecorr (V)
Icorr (A/cm2)
Ecorr (V)
Icorr (A/cm2)
0.06 0.09 0.14 0.12
3.5 · 106 3.9 · 106 5.0 · 107 5.2 · 107
0.03 0.03 0.07 0.11
4.0 · 106 5.5 · 106 4.3 · 106 1.3 · 106
0.04 0.08 0.03 0.10
1.8 · 105 5.0 · 105 1.2 · 105 4.2 · 106
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A. Dhawan et al. / Journal of Non-Crystalline Solids 353 (2007) 2619–2623 Polarization studies of Zr 67Ni33
Plot of Icorr vs Concentration -4
10
2.0
Zr65Cu17.5Ni10Al7.5 Zr46.75Ti8.25Cu7.5Ni10Be27.5 Zr67Ni33 Ti60Ni40
0.2 M HNO3 0.5 M HNO3 1.0 M HNO3
1.5
a
1.0
b
Icorr [A/cm ]
2
E[V]
c 0.5 0.0
-5
10
-0.5 -1.0 -6
10
-1.5 -9
10
-8
-7
10
10
-6
10
-5
-4
10
-3
10
10
-2
-1
10
10
2
I [A/cm ]
0.2
Fig. 3. Potentiodynamic polarization plots of amorphous alloy Zr67Ni33 in (a) 0.2 M HNO3; (b) 0.5 M HNO3; and (c) 1.0 M HNO3.
Polarization studies of Ti60Ni40
0.2 M HNO3 0.5 M HNO3 1.0 M HNO3
b
E[V]
c
0.5
0.0
-0.5
-1.0 -8
10
-7
10
-6
10
0.8
1.0
Fig. 5. Variation of corrosion current density (Icorr) for all the amorphous alloys versus concentration of HNO3.
4. Discussion a
1.0
0.6
1.0 M HNO3 solutions while its value in 0.2 M HNO3 is comparable to that of the other binary alloy Zr67Ni33.
2.0
1.5
0.4
Concentration of HNO3 (M)
-5
10
-4
10
-3
10
2
I [A/cm ] Fig. 4. Potentiodynamic polarization plots of amorphous alloy Ti60Ni40 in (a) 0.2 M HNO3; (b) 0.5 M HNO3; and (c) 1.0 M HNO3.
bulk amorphous alloy Zr46.75Ti8.25Cu7.5Ni10Be27.5 displays the highest value of Icorr followed by the other bulk amorphous alloy Zr65Cu17.5Ni10Al7.5, the binary amorphous alloys Zr67Ni33 and Ti60Ni40. Our results suggest that Zrbased bulk amorphous alloys do not seem to possess superior corrosion resistance vis-a`-vis conventional-type Zrand Ti-based amorphous alloys. On the contrary the bulk amorphous alloy Zr46.75Ti8.25Cu7.5Ni10Be27.5 is most prone to corrosion in comparison to the other amorphous alloys (Table 1 and Fig. 5) while the corrosion resistance of the other bulk alloy Zr65Cu17.5Ni10Al7.5 is also poorer than that of the binary alloys. The value of Icorr for the binary Zr67Ni33 in 0.2 M HNO3 is lower than that for the bulk amorphous alloy Zr65Cu17.5Ni10Al7.5 by about an order of magnitude, but in higher concentrations the Icorr values for both the alloys are comparable. The binary amorphous Ti60Ni40 exhibits the lowest value of Icorr in 0.5 M and
It is possible to understand the corrosion behavior of investigated alloys in HNO3 in terms of the differences in the nature of the anodic oxide films formed on surfaces of these alloys as reported in the literature [7,10,11,17– 22]. The anodic oxide films on amorphous Zr67Ni33 in 1 N HCl, 1 N HNO3 and 1 N H2SO4 [7] and on amorphous Ti50Cu50 [17] have been shown to consist of ZrO2/Zr(OH)2 and TiO2, respectively. On the other hand it has been reported that the anodic oxide film formed on the bulk amorphous alloy Zr65Cu17.5Ni10Al7.5 in phosphate-buffered solution [10] and on Zr55Al10Cu30Ni5 in 0.1 M Na2SO4 [11,18] are complex oxide films consisting of ZrO2 as major oxide in addition to the other alloying elements Al, Cu and Ni. It was shown by Gebert et al. [18] that the complex anodic oxide film formed on amorphous Zr55Al10Cu30Ni5 in 0.1 M Na2SO4 has poor protective quality than the film formed on pure Zr in the same aqueous medium. It is further noteworthy here that native oxide films formed on Zr-based multicomponent Zr65Cu17.5Ni10Al7.5 and Zr46.75Ti8.25Cu7.5Ni10Be27.5 [19] have also been found to be complex in nature consisting of oxides of several alloy constituents in contrast to those formed on binary Zr67Ni33 [20] and Ti60Ni40 [21] amorphous alloys. In this connection it is seen from Table 1 that the open circuit potential Ecorr for bulk amorphous alloys are nobler than those for the binary alloys, thus suggesting the presence of other alloying elements like Cu, Ni, Al or Be during anodic film formation on the multicomponent bulk amorphous alloys. Similar observations have been made by Hiromoto et al. [10] during corrosion studies on amorphous Zr65Cu17.5Ni10Al7.5 in phosphate-buffered
A. Dhawan et al. / Journal of Non-Crystalline Solids 353 (2007) 2619–2623
solution and the shift of the OCP towards the nobler side has been attributed to the presence of Cu and Ni in the surface oxide film. The possible explanation for the lowest value of Icorr in the case of amorphous Ti60Ni40 alloy as compared to the binary and the bulk amorphous alloys could be attributed to the formation of a strong and protective film of TiO2 on the alloy surface. The formation of a strong passive film of TiO2 during the anodic polarization of the Ti60Ni40 alloy is also suggested by the observed large passivity regions as shown in Fig. 4. It has been further reported that oxide film formed on Ti-based amorphous alloys are more rigid compared to those formed on Zr-based alloys and it has been attributed to the greater affinity of Ti for oxygen atoms [22]. From the above discussion it may be mentioned in regard to the investigations reported here that the anodic oxide films formed on binary alloys Zr67Ni33 and Ti60Ni40 are likely to be more homogeneous and uniform with a better protective quality than the complex oxide films formed on multicomponent bulk amorphous alloys Zr65Cu17.5Ni10Al7.5 and Zr46.75Ti8.25Cu7.5Ni10Be27.5. It is thus suggested from the above discussion that the bulk amorphous alloys Zr65Cu17.5Ni10Al7.5 and Zr46.75Ti8.25Cu7.5Ni10Be27.5 are not superior to binary conventional-type amorphous alloys Zr67Ni33 and Ti60Ni40 so far as their corrosion resistance in aqueous HNO3 is concerned. In contrast, bulk alloy Zr46.75Ti8.25Cu7.5Ni10Be27.5 seems to be more prone to corrosion in comparison to the other alloys and the conventional-type binary amorphous alloy Ti60Ni40 displays the maximum resistance to corrosion in aqueous HNO3 solution. 5. Conclusions i) The corrosion current density was found to be maximum for the bulk amorphous alloy Zr46.75Ti8.25Cu7.5Ni10Be27.5 followed by that for the other bulk amorphous alloy Zr65Cu17.5Ni10Al7.5 and binary alloys Zr67Ni33, Ti60Ni40 in 0.2 M, 0.5 M and 1.0 M HNO3 aqueous solutions. ii) It is suggested that the bulk amorphous alloys Zr65Cu17.5Ni10Al7.5 and Zr46.75Ti8.25Cu7.5Ni10Be27.5 are not superior to conventional amorphous alloys Zr67Ni33 and Ti60Ni40 so far as their corrosion behavior in aqueous HNO3 is concerned.
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Acknowledgements The Financial support for this work under DAE/BRNS Research Project (Grants No. 99/37/25/BRNS) is gratefully acknowledged. Thanks are due to Dr M.-P. Macht, HMI Berlin for giving us the amorphous alloy specimens for this work. References [1] T. Zhang, A. Inoue, T. Masumoto, Mater. Trans. JIM 32 (1991) 1005. [2] W.L. Johnson, Curr. Opin. Solid St. M. 1 (1996) 383. [3] A. Pecker, W.L. Johnson, Appl. Phys. Lett. 63 (1993) 2342. [4] M.W. Tan, E. Akiyama, A. Kawashima, K. Asami, K. Hasimoto, Corros. Sci. 38 (1996) 349. [5] K. Asami, M. Naka, K. Hasimoto, T. Masumoto, J. Electrochem. Soc. 127 (1980) 2130. [6] R.B. Diegle, Corrosion 35 (1979) 250. [7] G.K. Dey, R.T. Savalia, S.K. Sharma, S.K. Kulkarni, Corros. Sci. 29 (1989) 823. [8] V. Schroeder, C.J. Gilbert, R.O. Ritchie, Scr. Mater. 38 (1998) 1481. [9] S. Hiromoto, A.-P. Tsai, M. Sumita, T. Hanawa, Corros. Sci. 42 (2000) 1651. [10] S. Hiromoto, A.-P. Tsai, M. Sumita, T. Hanawa, Corros. Sci. 42 (2000) 2167. [11] K. Bulchholz, A. Gebert, K. Mummert, J. Eckert, L. Schultz, Mat. Res. Soc. Symp. Proc. 554 (1999) 161. [12] W.H. Peter, R.A. Buchanan, C.T. Liu, P.K. Liaw, M.L. Morrison, J.A. Horton, C.A. Carmichael Jr., J.L. Wright, Intermetallics 10 (2002) 1157. [13] R.S. Dutta, R.T. Savalia, G.K. Dey, Scr. Metall. Mater. 32 (1995) 207. [14] R.S. Dutta, R.T. Savalia, G.K. Dey, Brit. Corros. J. 36 (2001) 221. [15] A. Dhawan, S. Roychowdhury, P.K. De, S.K. Sharma, J. Non-Cryst. Solids 351 (2005) 951. [16] M. Stern, A.L. Geary, J. Electrochem. Soc. 104 (1957) 56. [17] R. Schennach, S. Promreuk, D.G. Naugle, D.L. Cocke, Oxid. Met. 55 (5/6) (2001) 523. [18] A. Gebert, K. Buchholz, A. Leonhard, K. Mummert, J. Eckert, L. Schultz, Mater. Sci. Eng. A 267 (1999) 294. [19] S.K. Sharma, T. Strunskus, H. Ladebusch, F. Faupel, Mater. Sci. Eng. A 304–306 (2001) 747. [20] D.L. Cocke, G. Liang, M. Owens, D.E. Halverson, D.G. Naugle, Mater. Sci. Eng. 99 (1988) 497. [21] P. Srivastava, S. Venkatesh, M. Khaled, K.B. Garg, S.K. Sharma, in: Proceedings of DAE Solid State Physics (SSP-94), University of Rajasthan, Jaipur, 27–31, December, 1994, p. 457. [22] Choll-Hong Hawang, Kangio Cho, Kazutaka Kawamura, Raipdly Quenched Metals, in: S. Steeb, H. Warlimont (Eds.), Elsevier Science, 1985, p. 1469.