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Deformation bands in metallic glasses induced by swift heavy ions
NIM B Beam Interactions with Materials & Atoms
Nuclear Instruments and Methods in Physics Research B 245 (2006) 130–132 www.elsevier.com/locate/nimb
Deformation bands in metallic glasses induced by swift heavy ions G. Rizza a
a,*
, A. Dunlop a, M. Kopcewicz
q
b
Laboratoire des Solides Irradie´s, Commissariat a` l’Energie Atomique/Ecole Polytechnique, 91128 Palaiseau, France b Institute of Electronic Materials Technology, Wolczynska 133, 01-919 Warszawa, Poland Available online 6 January 2006
Abstract We present a direct experimental evidence that shear bands in metallic glasses can be induced by swift heavy ion irradiation. Transmission electron microscopy micrographs show that shear bands nucleate in the vicinity of the ion paths. Finally, we state that swift heavy-ion irradiation can be used as a nanometer-size probe to test the structural stability of metallic glasses under high local stresses. 2005 Elsevier B.V. All rights reserved. PACS: 61.80.Jh; 62.50.+p; 68.37.Lp; 83.50.v Keywords: Transmission electron microscopy; Swift heavy ions; Metallic glasses; Shear bands; Shock waves
1. Introduction The mechanical properties of amorphous alloys have become topics of scientific and technological interest in terms of structural and functional applications. For this reason, the structural stability of metallic glasses has been the focus of many theoretical and experimental investigations [1–3]. It was experimentally found that metallic glasses deform homogeneously at high temperature and/or low strain rate whereas they deform inhomogeneously at low temperature and/or high strain rate. In this latter case, the deformation is localized in thin bands, called shear or deformation bands. Indentation experiments are an example of high strain rate mechanisms which lead to the formation of shear bands. However the basic mechanisms of shear bands formation are not completely clarified. There is consequently much interest in understanding the microscopic mechanisms of structural relaxation under stress. A submicrometer scale structural investigation of shear band formation, however, is quite difficult because of the macroq Irradiation performed at the Tandem accelerator, Nuclear Physics Institute, Orsay, France. * Corresponding author. Tel.: +33 1 69 33 45 10; fax: +33 1 69 33 30 22. E-mail address: [email protected] (G. Rizza).
0168-583X/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.11.089
scopic level of the experimental set-up. As a swift heavy ion induces a localized shear stress accompanied by a large strain rate and the generation of an outgoing pressure wave [4,5], it is in principle possible to overcome the above difficulty to perform sub-micrometer scale experiments using individual ions as nanometer probes to test the stability of metallic glasses under very local stresses. Therefore, in the same way as shear bands were formed during macroscopic high strain rate experiments, deformation bands should expected to be found close to the ion track. Here, we report the direct observation by transmission electron microscopy (TEM) of heavy-ion irradiation-induced deformation bands in Fe-based amorphous alloys. 2. Experimental The possibility to induce shear bands by swift heavy ions irradiation was studied for different Fe-based metallic glasses. Here we report results concerning two of them: specifically, Fe73.5Cu1Nb3Si13.5B9 and Fe90Zr7B3. In order to have the largest mechanical effect, the specimens were irradiated at 300 K with 30 MeV C60 cluster ions, using the Tandem accelerator facility of Nuclear Physics Institute in Orsay, France. The samples were irradiated up to a fluence of 1010 cm2, and the linear rate of energy deposition
G. Rizza et al. / Nucl. Instr. and Meth. in Phys. Res. B 245 (2006) 130–132
into electronic processes was estimated using SRIM2000 code to be about Se 80 keV nm1. To avoid any mechanical deformation due to sample preparation, specimens in the form of 3 mm diameter discs have been electrochemically prethinned. Earlier studies of the shear band produced in melt spun ribbons using TEM technique have shown that contrast from the shear band was different from the rest of the sample [6]. In particular, shear bands present a brighter contrast with respect to the surrounding matrix, which can be interpreted as a region of reduced thickness and/or reduced density. Thus, possible microstructural changes associated with irradiation-induced shear bands formation were investigated by observing the same regions before and after irradiation using conventional TEM and high resolution TEM (HRTEM) techniques. The irradiation-induced microstructural evolution of the samples was studied using a 300 kV transmission electron microscope. TEM micrographs were processed with a slow scan CCD camera and analyzed with Digital Micrograph program. The TEM observations were always performed using a very low electron flux in order to avoid any structural modification of the sample due to the electron beam.
131
geneous structure. In other words, neither cracks nor shear bands are visible. The continuous change in contrast, from brighter contrast at the very edge of the sample to a darker contrast towards the bulk, is ascribed to the thickness increase of the specimen. The same region of the sample irradiated with C60 cluster ions up to a fluence of 1 · 1010 cm2 is shown in Fig. 1(b). Two main differences can be observed: (i) white, almost circular spots
3. Results Fig. 1(a) shows a TEM micrograph of non-irradiated Fe90Zr7B3 amorphous alloy. The sample exhibits a homoFig. 2. Bright field transmission electron micrograph of Fe73.5Cu1Nb3Si13.5B9 amorphous alloy irradiated up to a fluence of 1 · 1010 cm2 with 30 MeV C60. Local plastic deformation towards the sample edge and a deformation band, in the opposite direction, are visible.
Fig. 1. (a) Bright field transmission electron micrograph of unirradiated Fe90Zr7B3 amorphous alloy. (b) The same region irradiated up to a fluence of 1 · 1010 cm2 with 30 MeV C60. The deformation band is indicated by the arrow.
Fig. 3. High resolution transmission electron micrograph of an isolated track in an Fe73.5Nb4.5Cr5Cu1B16 sample irradiated to a fluence of 1 · 1010 cm2 with 30 MeV C60. A deformation band which exits toward the sample edge is visible.
132
G. Rizza et al. / Nucl. Instr. and Meth. in Phys. Res. B 245 (2006) 130–132
corresponding to the impacts of the projectiles (ion tracks) are clearly visible, (ii) in the region indicated by the arrow a bright contrast band appears. This ‘‘band’’ appears to be 10 nm wide and more than 100 nm long. The fact that inside the band at least two ion tracks are visible, indicates that the band was generated by the irradiation. Fig. 2 shows an ion track, with a diameter of 8 nm, which is very close to the sample edge. Moreover, the micrograph shows how the energy deposited by the ion can relax inducing a local plastic deformation towards the sample edge. Symmetrically, a shear band clearly generated by the ion track, 6–8 nm wide and 20 nm long, developed in the opposite direction. Fig. 3 shows another example of a deformation band generated from a single ion track. This band is 10 nm wide and 30 nm long, it is slightly curled and exits towards the central hole. It is worthily to note that shear band formation does not occur only when the track is found very close to the central hole, but also when the track is at a certain distance from it. The important consequence of this observation is that structural relaxation does take place only very close to the ion track, where the stress level is higher, but once the band is generated it can propagate towards mesoscopic distances.
and propagation of these STZs allows the nucleation of the shear band. To be more quantitative, the effect of the single ion-induced local stress can be estimated using the visco-elastic model [4,5] to be
4. Discussion
Acknowledgements
Following the free volume model for metallic glasses [7,8], a defect is a region of excess free volume. The excess free volume can be created by an applied stress when an atom is squeezed into a hole smaller than itself. In general, the excess free volume is not due to a single atom but is a cooperative transformation of a cluster of atoms, called shear transformation zones (STZ), between two metastable states [9,10]. When many STZ operate together, shear strain localizes into shear bands. This localization is active when the strain rate is high [10,11]. Therefore, a phenomenological mechanism to explain the formation of shear bands during irradiation can be proposed. The pressure wave formed in the wake of the projectile, generates an outgoing transient stress and strain, which allows nucleation of the shear transformation zones. As the nucleation rate of the STZs is proportional to the strain rate, and a swift heavy ion induces a localized shear stress accompanied by a large strain rate (_e 106 –109 s1 [12]), coalescence
The authors are grateful to the staff of the IPN Orsay for their very efficient help during the irradiation, in particular to S. Della-Negra.
rtrack ¼
ð1 þ 2mÞ EaDT 3 GPa; 2ð1 mÞð5 4mÞ
ð1Þ
where E = 150 GPa is the Young’s modulus, m = 0.4 the Poisson ratio, a 4.5 · 105 K1 the linear thermal expansion coefficient and DT* 103 K the effective temperature inside the track. Because the stress around the track is higher than the yield strength of the material (ryield 1.8 GPa), the surrounding matrix undergoes substantial deformation and shear bands can be generated. In conclusion, the present work provides a direct experimental evidence that heavy-ion irradiation of Fe-based amorphous alloys at room temperature results in shear band formation. The result is important both to understand the mechanism of energy conversion into atomic movent during electronic excitation and to give an insight into the basic mechanisms of structural relaxation of an amorphous structure under sub-micrometer shear stress application.
References [1] F. Spaepen, Physics of Defects, Les Houches, Session XXXV, Elsevier, North-Holland, 1980, p. 136. [2] T.C. Haufnagel, P. El-Deiry, R.P. Vinci, Scr. Mater. 43 (2000) 1071. [3] K.M. Flores, R.H. Dauskardt, Acta Mater. 49 (2001) 2527. [4] H. Trinkaus, J. Nucl. Mater. 223 (1995) 196. [5] H. Trinkaus, A.I. Ryazanov, Phys. Rev. Lett. 74 (1995) 5072. [6] P.E. Donovan, W.M. Stobbs, Acta Metall. 29 (1981) 1419. [7] F. Spaepen, Acta Metall. 25 (1977) 407. [8] A.I. Taub, F. Spaepen, Acta Metall. 28 (1980) 1781. [9] A.S. Argon, Acta Metall. 27 (1979) 47. [10] M.L. Falk, J.S. Langer, Phys. Rev. E 57 (1998) 7192. [11] M.L. Falk, Phys. Rev. B 60 (1999) 7062. [12] S. Klaumu¨nzer, C. Li, S. Lo¨ffler, M. Rammensee, G. Schumacher, H.CH. Neitzert, Rad. Def. Sol. 108 (1989) 131.
Nuclear Instruments and Methods in Physics Research B 245 (2006) 130–132 www.elsevier.com/locate/nimb
Deformation bands in metallic glasses induced by swift heavy ions G. Rizza a
a,*
, A. Dunlop a, M. Kopcewicz
q
b
Laboratoire des Solides Irradie´s, Commissariat a` l’Energie Atomique/Ecole Polytechnique, 91128 Palaiseau, France b Institute of Electronic Materials Technology, Wolczynska 133, 01-919 Warszawa, Poland Available online 6 January 2006
Abstract We present a direct experimental evidence that shear bands in metallic glasses can be induced by swift heavy ion irradiation. Transmission electron microscopy micrographs show that shear bands nucleate in the vicinity of the ion paths. Finally, we state that swift heavy-ion irradiation can be used as a nanometer-size probe to test the structural stability of metallic glasses under high local stresses. 2005 Elsevier B.V. All rights reserved. PACS: 61.80.Jh; 62.50.+p; 68.37.Lp; 83.50.v Keywords: Transmission electron microscopy; Swift heavy ions; Metallic glasses; Shear bands; Shock waves
1. Introduction The mechanical properties of amorphous alloys have become topics of scientific and technological interest in terms of structural and functional applications. For this reason, the structural stability of metallic glasses has been the focus of many theoretical and experimental investigations [1–3]. It was experimentally found that metallic glasses deform homogeneously at high temperature and/or low strain rate whereas they deform inhomogeneously at low temperature and/or high strain rate. In this latter case, the deformation is localized in thin bands, called shear or deformation bands. Indentation experiments are an example of high strain rate mechanisms which lead to the formation of shear bands. However the basic mechanisms of shear bands formation are not completely clarified. There is consequently much interest in understanding the microscopic mechanisms of structural relaxation under stress. A submicrometer scale structural investigation of shear band formation, however, is quite difficult because of the macroq Irradiation performed at the Tandem accelerator, Nuclear Physics Institute, Orsay, France. * Corresponding author. Tel.: +33 1 69 33 45 10; fax: +33 1 69 33 30 22. E-mail address: [email protected] (G. Rizza).
0168-583X/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.11.089
scopic level of the experimental set-up. As a swift heavy ion induces a localized shear stress accompanied by a large strain rate and the generation of an outgoing pressure wave [4,5], it is in principle possible to overcome the above difficulty to perform sub-micrometer scale experiments using individual ions as nanometer probes to test the stability of metallic glasses under very local stresses. Therefore, in the same way as shear bands were formed during macroscopic high strain rate experiments, deformation bands should expected to be found close to the ion track. Here, we report the direct observation by transmission electron microscopy (TEM) of heavy-ion irradiation-induced deformation bands in Fe-based amorphous alloys. 2. Experimental The possibility to induce shear bands by swift heavy ions irradiation was studied for different Fe-based metallic glasses. Here we report results concerning two of them: specifically, Fe73.5Cu1Nb3Si13.5B9 and Fe90Zr7B3. In order to have the largest mechanical effect, the specimens were irradiated at 300 K with 30 MeV C60 cluster ions, using the Tandem accelerator facility of Nuclear Physics Institute in Orsay, France. The samples were irradiated up to a fluence of 1010 cm2, and the linear rate of energy deposition
G. Rizza et al. / Nucl. Instr. and Meth. in Phys. Res. B 245 (2006) 130–132
into electronic processes was estimated using SRIM2000 code to be about Se 80 keV nm1. To avoid any mechanical deformation due to sample preparation, specimens in the form of 3 mm diameter discs have been electrochemically prethinned. Earlier studies of the shear band produced in melt spun ribbons using TEM technique have shown that contrast from the shear band was different from the rest of the sample [6]. In particular, shear bands present a brighter contrast with respect to the surrounding matrix, which can be interpreted as a region of reduced thickness and/or reduced density. Thus, possible microstructural changes associated with irradiation-induced shear bands formation were investigated by observing the same regions before and after irradiation using conventional TEM and high resolution TEM (HRTEM) techniques. The irradiation-induced microstructural evolution of the samples was studied using a 300 kV transmission electron microscope. TEM micrographs were processed with a slow scan CCD camera and analyzed with Digital Micrograph program. The TEM observations were always performed using a very low electron flux in order to avoid any structural modification of the sample due to the electron beam.
131
geneous structure. In other words, neither cracks nor shear bands are visible. The continuous change in contrast, from brighter contrast at the very edge of the sample to a darker contrast towards the bulk, is ascribed to the thickness increase of the specimen. The same region of the sample irradiated with C60 cluster ions up to a fluence of 1 · 1010 cm2 is shown in Fig. 1(b). Two main differences can be observed: (i) white, almost circular spots
3. Results Fig. 1(a) shows a TEM micrograph of non-irradiated Fe90Zr7B3 amorphous alloy. The sample exhibits a homoFig. 2. Bright field transmission electron micrograph of Fe73.5Cu1Nb3Si13.5B9 amorphous alloy irradiated up to a fluence of 1 · 1010 cm2 with 30 MeV C60. Local plastic deformation towards the sample edge and a deformation band, in the opposite direction, are visible.
Fig. 1. (a) Bright field transmission electron micrograph of unirradiated Fe90Zr7B3 amorphous alloy. (b) The same region irradiated up to a fluence of 1 · 1010 cm2 with 30 MeV C60. The deformation band is indicated by the arrow.
Fig. 3. High resolution transmission electron micrograph of an isolated track in an Fe73.5Nb4.5Cr5Cu1B16 sample irradiated to a fluence of 1 · 1010 cm2 with 30 MeV C60. A deformation band which exits toward the sample edge is visible.
132
G. Rizza et al. / Nucl. Instr. and Meth. in Phys. Res. B 245 (2006) 130–132
corresponding to the impacts of the projectiles (ion tracks) are clearly visible, (ii) in the region indicated by the arrow a bright contrast band appears. This ‘‘band’’ appears to be 10 nm wide and more than 100 nm long. The fact that inside the band at least two ion tracks are visible, indicates that the band was generated by the irradiation. Fig. 2 shows an ion track, with a diameter of 8 nm, which is very close to the sample edge. Moreover, the micrograph shows how the energy deposited by the ion can relax inducing a local plastic deformation towards the sample edge. Symmetrically, a shear band clearly generated by the ion track, 6–8 nm wide and 20 nm long, developed in the opposite direction. Fig. 3 shows another example of a deformation band generated from a single ion track. This band is 10 nm wide and 30 nm long, it is slightly curled and exits towards the central hole. It is worthily to note that shear band formation does not occur only when the track is found very close to the central hole, but also when the track is at a certain distance from it. The important consequence of this observation is that structural relaxation does take place only very close to the ion track, where the stress level is higher, but once the band is generated it can propagate towards mesoscopic distances.
and propagation of these STZs allows the nucleation of the shear band. To be more quantitative, the effect of the single ion-induced local stress can be estimated using the visco-elastic model [4,5] to be
4. Discussion
Acknowledgements
Following the free volume model for metallic glasses [7,8], a defect is a region of excess free volume. The excess free volume can be created by an applied stress when an atom is squeezed into a hole smaller than itself. In general, the excess free volume is not due to a single atom but is a cooperative transformation of a cluster of atoms, called shear transformation zones (STZ), between two metastable states [9,10]. When many STZ operate together, shear strain localizes into shear bands. This localization is active when the strain rate is high [10,11]. Therefore, a phenomenological mechanism to explain the formation of shear bands during irradiation can be proposed. The pressure wave formed in the wake of the projectile, generates an outgoing transient stress and strain, which allows nucleation of the shear transformation zones. As the nucleation rate of the STZs is proportional to the strain rate, and a swift heavy ion induces a localized shear stress accompanied by a large strain rate (_e 106 –109 s1 [12]), coalescence
The authors are grateful to the staff of the IPN Orsay for their very efficient help during the irradiation, in particular to S. Della-Negra.
rtrack ¼
ð1 þ 2mÞ EaDT 3 GPa; 2ð1 mÞð5 4mÞ
ð1Þ
where E = 150 GPa is the Young’s modulus, m = 0.4 the Poisson ratio, a 4.5 · 105 K1 the linear thermal expansion coefficient and DT* 103 K the effective temperature inside the track. Because the stress around the track is higher than the yield strength of the material (ryield 1.8 GPa), the surrounding matrix undergoes substantial deformation and shear bands can be generated. In conclusion, the present work provides a direct experimental evidence that heavy-ion irradiation of Fe-based amorphous alloys at room temperature results in shear band formation. The result is important both to understand the mechanism of energy conversion into atomic movent during electronic excitation and to give an insight into the basic mechanisms of structural relaxation of an amorphous structure under sub-micrometer shear stress application.
References [1] F. Spaepen, Physics of Defects, Les Houches, Session XXXV, Elsevier, North-Holland, 1980, p. 136. [2] T.C. Haufnagel, P. El-Deiry, R.P. Vinci, Scr. Mater. 43 (2000) 1071. [3] K.M. Flores, R.H. Dauskardt, Acta Mater. 49 (2001) 2527. [4] H. Trinkaus, J. Nucl. Mater. 223 (1995) 196. [5] H. Trinkaus, A.I. Ryazanov, Phys. Rev. Lett. 74 (1995) 5072. [6] P.E. Donovan, W.M. Stobbs, Acta Metall. 29 (1981) 1419. [7] F. Spaepen, Acta Metall. 25 (1977) 407. [8] A.I. Taub, F. Spaepen, Acta Metall. 28 (1980) 1781. [9] A.S. Argon, Acta Metall. 27 (1979) 47. [10] M.L. Falk, J.S. Langer, Phys. Rev. E 57 (1998) 7192. [11] M.L. Falk, Phys. Rev. B 60 (1999) 7062. [12] S. Klaumu¨nzer, C. Li, S. Lo¨ffler, M. Rammensee, G. Schumacher, H.CH. Neitzert, Rad. Def. Sol. 108 (1989) 131.