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Dope depth distribution in rapidly solidified Al–Ge and Al–Me (Me=Fe, Cu, Sb) alloys
Journal of Alloys and Compounds 299 (2000) 205–207
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Dope depth distribution in rapidly solidified Al–Ge and Al–Me (Me5Fe, Cu, Sb) alloys I.I. Tashlykova-Bushkevich*, V.G. Shepelevich Byelorussian State University, Department of Solid State Physics,4 F. Skoryny pr., 220080 Minsk, Belarus Received 15 October 1999; accepted 12 November 1999
Abstract A detailed dope depth distribution investigation in rapidly solidified (RS) foils of Al alloys has been made using the Rutherford backscattering spectroscopy technique. We found that at the foil surface (0.04–0.06 mm) the dope concentration exceeds the experimental measured concentration. We also found that the Me concentration oscillates through the thickness of the investigated layers. However, in the RS Al–Ge alloy no dope oscillation was detected. 2000 Elsevier Science S.A. All rights reserved. Keywords: Rapid solidification; Aluminium alloys; RBS measurements; Depth distribution
Rapid solidification processing (RSP) of Al alloys is being used increasingly for the manufacture of aluminium alloys which have the advantage of highly improved properties in a variety of applications [1]. There has been a wide variety of different reports about the as-rapidly solidified (RS) microstructure of RS aluminium alloys, but insufficient attention has been devoted to the study of dope depth distribution in samples. The objective of the present work therefore, was to investigate the dope depth distribution in RS Al alloys using Rutherford backscattering spectroscopy (RBS). We have studied Al alloys with a dope concentration spanning the solid solubility range in aluminium alloys quenched from melt [1,2].
tangential velocity of 16 m?s 21 . Selected for the study were foils typically 30–60 mm thick and 5–10 mm wide. The surfaces that were chilled in contact with the cooper drum during solidification have been studied. The composition and the dope depth distribution of the RS foils were analysed by the RBS technique using He ions with an energy of 2.0 MeV. It allowed detection of the dopes in the foil surface region approximately up to 1.2 mm in thickness (the grain radius on the investigated foil surface of the alloys is larger than 1.2 mm). The energy resolutions of the detecting systems were 15 and 25 keV in the investigation of the Al–Cu, Sb and the Al–Fe, Ge alloys, respectively. Therefore the layer alloy analysis thickness during the RUMP simulation [3] was chosen to be equal to 0.03 or 0.04 mm.
2. Experimental
3. Results and discussion
Alloys of the nominal compositions Al-2.0 at.% Fe, Al-2.1 at.% Cu, Al-1.6 at.% Sb and Al-1.6 at.% Ge alloys were manufactured by melting high purity aluminium and dope in a quartz tube in a nitrogen atmosphere. Specimens of each ingot were rapidly solidified (cooling rate was of the order of 10 6 K / c) by ejection through an orifice onto the inner surface of a cooper drum rotating with a
This paper describes new results of a continued study of the depth dope distribution in RS aluminium alloys. In comparison with preliminary RBS spectra investigations [4,5] the use of computer simulations has allowed us to carry out firstly a precise definition of alloy composition and secondly a layer analysis of the depth dope distribution in the foils. Fig. 1 shows backscattering energy spectra from RS foils of Al–Cu and Al–Ge alloys. The corresponding depth dope distribution plots, which were constructed using RUMP simulation, are shown in Fig. 1c and d. Similar data were
1. Introduction
*Corresponding author. E-mail address: [email protected] (I.I. Tashlykova-Bushkevich)
0925-8388 / 00 / $ – see front matter 2000 Elsevier Science S.A. All rights reserved. PII: S0925-8388( 99 )00750-1
I.I. Tashlykova-Bushkevich, V.G. Shepelevich / Journal of Alloys and Compounds 299 (2000) 205 – 207
206
Fig. 1. Backscattering energy spectra of 4 He ions with Eo 52 MeV from rapidly solidified foils of (a) Al–Cu and (b) Al–Ge alloys and corresponding dope depth distribution plots (c) and (d), respectively.
obtained for Al–Fe and Al–Sb alloys. The results are summarized in Table 1. We found that the RSP of Al–Me alloys produces a reduction of the Me concentration in the foil surface region. The largest deviations of the experimentally measured average dope concentration from the nominal dope concentration occurs in Al–Fe and Al– Sb alloys (see Table 1). At first we supposed that the lack of dope in the foils surface region is caused by the limited (1 at.% [6]) iron solubility in aluminium and the antimony volatility at the used temperatures [7]. We detected that the dope concentration at the foil surface (0.04–0.05 mm) for all studied foils is higher than the experimentally measured average dope concentration. The dope concentration in the near surface region of the Al–Fe and Al–Sb foil surfaces also exceeds the eutectic concentration [7] (see Table 1).
It has been found that there is no reduction of the dope concentration in the Al-1.6 at.% Ge foil, the experimentally measured average germanium concentration in the studied foil volume (excepting the region at the foil surface) being in accordance with the nominal concentration. In the foil surface region (0.06 mm) the germanium concentration exceeds the experimentally measured average concentration, but it is lower than the eutectic concentration [7]. The experimental data (Fig. 1a and b) reveal that there is an increase in the dope concentration towards the extremities of the grains that reach the foil surface. Dope segregation into the cell boundaries of RS alloys has been reported in [8–11]. The obtained results (see Table 1) qualitatively confirm a general crystallization model of
Table 1 Nominal and experimental measured dope concentrations, distance and relative amplitude of dope concentration oscillations in foil surface layers in contact with the cooper drum during the rapid solidification of the Al alloys Dope
Nominal dope concentration (at.%)
Average measured dope concentration (at.%)
Dope concentration at surface (at.%)
Average distance of oscillations (nm)
Average relative amplitude of oscillations
Fe Cu Sb Ge
2.0 2.1 1.6 1.6
0.37 1.62 0.3 1.6
2.0 3.0 0.9 3.5
80 74 79 No oscillations
0.75 0.29 0.42 –
I.I. Tashlykova-Bushkevich, V.G. Shepelevich / Journal of Alloys and Compounds 299 (2000) 205 – 207
rapidly solidified Al–Ge alloys presented by Ramachandrarao et al. [10]. In this model the recorded increase in solute concentration at the grain boundaries is explained by transient effect associated with the termination of crystal growth. However, the fact of a monotonous increase of the dope concentration with increasing depth in the foil surface region behind the dope concentration spike (Fig. 1c and d) is at variance with the crystallization model of RS aluminium alloys presented by Wang et al. [11]. Using computer simulation we found that the Me concentration oscillates through the thickness of the investigated alloys layers (Fig. 1c). We derived values for the distance between neighbouring maxima or minima of the Me concentration in aluminium and for the relative decrease in amplitude of the oscillations in the foils with increasing depth. The average relative of the oscillations was calculated as (Cmax 2 Cmin ) /Cmin , where Cmax and Cmin are the dope concentrations in the neighbouring maxima or minima of the Me depth distribution in aluminium. The distance and the average relative amplitude of the oscillations are the largest in the rapidly solidified Al-2.0 at.% Fe alloy (Table 1). The detected effect may probably be explained by a dope redistribution in the thin liquid zone ahead of the solid–liquid interface front because of recoalescence during RSP. In contrast with Al–Me alloys, no Ge oscillation is detected in the RS Al–Ge alloy. Thus the character of the dope distribution in the foil volume evidently depends on the different solidification mechanisms of the RSP. One of the reasons for such behaviour is probably the occurrence of different chemical bond types associated with the Ge and Me dopes in aluminium.
3.1. Conclusions We observed that the RSP of Al–Me alloys produces a reduction of the Me concentration in the foil surface region. In contrast with Me dopes, the experimental
207
measured average germanium concentration in the studied foil volume is in accordance with the nominal value. At the foil surface (0.04–0.06 mm) the dope concentration exceeds the experimentally measured average concentration. We found that the Me concentration oscillates through the thickness of the investigated layers within a thickness range corresponding to single solidified crystals. However, no dope oscillation were detected, in the RS Al–Ge alloy.
Acknowledgements One of the authors (I.I.T.-B.) would like to thank BRFFPI for partial financial support. I.I.T.-B. is also grateful to Professor G. Carter (University of Salford, UK) and Dr. V.S. Kulikauskas (Moscow State University, Russia) for their assistance with carrying out experiments by means of the RBS technique.
References [1] E.J. Lavernia, J.D. Ayers, T.S. Srivatson, Intern. Mater. Rev. 37 (1992) 1. [2] V.G. Shepelevich, I.I. Tashlykova-Bushkevich, L.A. Vasilyeva, Phys. Chem. Mater. Proc. 3 (1999) 69, (in Russian). [3] L.N. Doolittle, Nucl. Instr. Meth. B9 (1985) 344. [4] V. Shepelevich, I. Tashlykova-Bushkevich, Mater. Sci. Forum 248– 249 (1997) 385. [5] I.I. Tashlykova-Bushkevich, V.G. Shepelevich, Perspective Mater. 5 (1998) 31, (in Russian). [6] I.G. Brodova, V.O. Esin, I.V. Polents, I.P. Korshunov, V.M. Fedorov, T.L. Lebedeva, O.A. Kortsavina, P.S. Popel, Rasplavy 1 (1990) 16. [7] M. Hansen, K. Anderko, Condition Diagrams of Binary Alloys, Vol. 1, Gitilchimts, Moscow, 1962. [8] E.K. Ioannis, T. Scheppard, J. Mater. Sci. 25 (1990) 3965. [9] C. Hayzelden, J.J. Rayment, B. Cantor, Acta Metall. 31 (1983) 379. [10] P. Ramachandrarao, M.G. Scott, G.A. Chadwick, Phil. Mag. 25 (1972) 961. [11] G.-X. Wang, V. Prasad, E.F. Matthys, J. Cryst. Growth 174 (1997) 35.
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Dope depth distribution in rapidly solidified Al–Ge and Al–Me (Me5Fe, Cu, Sb) alloys I.I. Tashlykova-Bushkevich*, V.G. Shepelevich Byelorussian State University, Department of Solid State Physics,4 F. Skoryny pr., 220080 Minsk, Belarus Received 15 October 1999; accepted 12 November 1999
Abstract A detailed dope depth distribution investigation in rapidly solidified (RS) foils of Al alloys has been made using the Rutherford backscattering spectroscopy technique. We found that at the foil surface (0.04–0.06 mm) the dope concentration exceeds the experimental measured concentration. We also found that the Me concentration oscillates through the thickness of the investigated layers. However, in the RS Al–Ge alloy no dope oscillation was detected. 2000 Elsevier Science S.A. All rights reserved. Keywords: Rapid solidification; Aluminium alloys; RBS measurements; Depth distribution
Rapid solidification processing (RSP) of Al alloys is being used increasingly for the manufacture of aluminium alloys which have the advantage of highly improved properties in a variety of applications [1]. There has been a wide variety of different reports about the as-rapidly solidified (RS) microstructure of RS aluminium alloys, but insufficient attention has been devoted to the study of dope depth distribution in samples. The objective of the present work therefore, was to investigate the dope depth distribution in RS Al alloys using Rutherford backscattering spectroscopy (RBS). We have studied Al alloys with a dope concentration spanning the solid solubility range in aluminium alloys quenched from melt [1,2].
tangential velocity of 16 m?s 21 . Selected for the study were foils typically 30–60 mm thick and 5–10 mm wide. The surfaces that were chilled in contact with the cooper drum during solidification have been studied. The composition and the dope depth distribution of the RS foils were analysed by the RBS technique using He ions with an energy of 2.0 MeV. It allowed detection of the dopes in the foil surface region approximately up to 1.2 mm in thickness (the grain radius on the investigated foil surface of the alloys is larger than 1.2 mm). The energy resolutions of the detecting systems were 15 and 25 keV in the investigation of the Al–Cu, Sb and the Al–Fe, Ge alloys, respectively. Therefore the layer alloy analysis thickness during the RUMP simulation [3] was chosen to be equal to 0.03 or 0.04 mm.
2. Experimental
3. Results and discussion
Alloys of the nominal compositions Al-2.0 at.% Fe, Al-2.1 at.% Cu, Al-1.6 at.% Sb and Al-1.6 at.% Ge alloys were manufactured by melting high purity aluminium and dope in a quartz tube in a nitrogen atmosphere. Specimens of each ingot were rapidly solidified (cooling rate was of the order of 10 6 K / c) by ejection through an orifice onto the inner surface of a cooper drum rotating with a
This paper describes new results of a continued study of the depth dope distribution in RS aluminium alloys. In comparison with preliminary RBS spectra investigations [4,5] the use of computer simulations has allowed us to carry out firstly a precise definition of alloy composition and secondly a layer analysis of the depth dope distribution in the foils. Fig. 1 shows backscattering energy spectra from RS foils of Al–Cu and Al–Ge alloys. The corresponding depth dope distribution plots, which were constructed using RUMP simulation, are shown in Fig. 1c and d. Similar data were
1. Introduction
*Corresponding author. E-mail address: [email protected] (I.I. Tashlykova-Bushkevich)
0925-8388 / 00 / $ – see front matter 2000 Elsevier Science S.A. All rights reserved. PII: S0925-8388( 99 )00750-1
I.I. Tashlykova-Bushkevich, V.G. Shepelevich / Journal of Alloys and Compounds 299 (2000) 205 – 207
206
Fig. 1. Backscattering energy spectra of 4 He ions with Eo 52 MeV from rapidly solidified foils of (a) Al–Cu and (b) Al–Ge alloys and corresponding dope depth distribution plots (c) and (d), respectively.
obtained for Al–Fe and Al–Sb alloys. The results are summarized in Table 1. We found that the RSP of Al–Me alloys produces a reduction of the Me concentration in the foil surface region. The largest deviations of the experimentally measured average dope concentration from the nominal dope concentration occurs in Al–Fe and Al– Sb alloys (see Table 1). At first we supposed that the lack of dope in the foils surface region is caused by the limited (1 at.% [6]) iron solubility in aluminium and the antimony volatility at the used temperatures [7]. We detected that the dope concentration at the foil surface (0.04–0.05 mm) for all studied foils is higher than the experimentally measured average dope concentration. The dope concentration in the near surface region of the Al–Fe and Al–Sb foil surfaces also exceeds the eutectic concentration [7] (see Table 1).
It has been found that there is no reduction of the dope concentration in the Al-1.6 at.% Ge foil, the experimentally measured average germanium concentration in the studied foil volume (excepting the region at the foil surface) being in accordance with the nominal concentration. In the foil surface region (0.06 mm) the germanium concentration exceeds the experimentally measured average concentration, but it is lower than the eutectic concentration [7]. The experimental data (Fig. 1a and b) reveal that there is an increase in the dope concentration towards the extremities of the grains that reach the foil surface. Dope segregation into the cell boundaries of RS alloys has been reported in [8–11]. The obtained results (see Table 1) qualitatively confirm a general crystallization model of
Table 1 Nominal and experimental measured dope concentrations, distance and relative amplitude of dope concentration oscillations in foil surface layers in contact with the cooper drum during the rapid solidification of the Al alloys Dope
Nominal dope concentration (at.%)
Average measured dope concentration (at.%)
Dope concentration at surface (at.%)
Average distance of oscillations (nm)
Average relative amplitude of oscillations
Fe Cu Sb Ge
2.0 2.1 1.6 1.6
0.37 1.62 0.3 1.6
2.0 3.0 0.9 3.5
80 74 79 No oscillations
0.75 0.29 0.42 –
I.I. Tashlykova-Bushkevich, V.G. Shepelevich / Journal of Alloys and Compounds 299 (2000) 205 – 207
rapidly solidified Al–Ge alloys presented by Ramachandrarao et al. [10]. In this model the recorded increase in solute concentration at the grain boundaries is explained by transient effect associated with the termination of crystal growth. However, the fact of a monotonous increase of the dope concentration with increasing depth in the foil surface region behind the dope concentration spike (Fig. 1c and d) is at variance with the crystallization model of RS aluminium alloys presented by Wang et al. [11]. Using computer simulation we found that the Me concentration oscillates through the thickness of the investigated alloys layers (Fig. 1c). We derived values for the distance between neighbouring maxima or minima of the Me concentration in aluminium and for the relative decrease in amplitude of the oscillations in the foils with increasing depth. The average relative of the oscillations was calculated as (Cmax 2 Cmin ) /Cmin , where Cmax and Cmin are the dope concentrations in the neighbouring maxima or minima of the Me depth distribution in aluminium. The distance and the average relative amplitude of the oscillations are the largest in the rapidly solidified Al-2.0 at.% Fe alloy (Table 1). The detected effect may probably be explained by a dope redistribution in the thin liquid zone ahead of the solid–liquid interface front because of recoalescence during RSP. In contrast with Al–Me alloys, no Ge oscillation is detected in the RS Al–Ge alloy. Thus the character of the dope distribution in the foil volume evidently depends on the different solidification mechanisms of the RSP. One of the reasons for such behaviour is probably the occurrence of different chemical bond types associated with the Ge and Me dopes in aluminium.
3.1. Conclusions We observed that the RSP of Al–Me alloys produces a reduction of the Me concentration in the foil surface region. In contrast with Me dopes, the experimental
207
measured average germanium concentration in the studied foil volume is in accordance with the nominal value. At the foil surface (0.04–0.06 mm) the dope concentration exceeds the experimentally measured average concentration. We found that the Me concentration oscillates through the thickness of the investigated layers within a thickness range corresponding to single solidified crystals. However, no dope oscillation were detected, in the RS Al–Ge alloy.
Acknowledgements One of the authors (I.I.T.-B.) would like to thank BRFFPI for partial financial support. I.I.T.-B. is also grateful to Professor G. Carter (University of Salford, UK) and Dr. V.S. Kulikauskas (Moscow State University, Russia) for their assistance with carrying out experiments by means of the RBS technique.
References [1] E.J. Lavernia, J.D. Ayers, T.S. Srivatson, Intern. Mater. Rev. 37 (1992) 1. [2] V.G. Shepelevich, I.I. Tashlykova-Bushkevich, L.A. Vasilyeva, Phys. Chem. Mater. Proc. 3 (1999) 69, (in Russian). [3] L.N. Doolittle, Nucl. Instr. Meth. B9 (1985) 344. [4] V. Shepelevich, I. Tashlykova-Bushkevich, Mater. Sci. Forum 248– 249 (1997) 385. [5] I.I. Tashlykova-Bushkevich, V.G. Shepelevich, Perspective Mater. 5 (1998) 31, (in Russian). [6] I.G. Brodova, V.O. Esin, I.V. Polents, I.P. Korshunov, V.M. Fedorov, T.L. Lebedeva, O.A. Kortsavina, P.S. Popel, Rasplavy 1 (1990) 16. [7] M. Hansen, K. Anderko, Condition Diagrams of Binary Alloys, Vol. 1, Gitilchimts, Moscow, 1962. [8] E.K. Ioannis, T. Scheppard, J. Mater. Sci. 25 (1990) 3965. [9] C. Hayzelden, J.J. Rayment, B. Cantor, Acta Metall. 31 (1983) 379. [10] P. Ramachandrarao, M.G. Scott, G.A. Chadwick, Phil. Mag. 25 (1972) 961. [11] G.-X. Wang, V. Prasad, E.F. Matthys, J. Cryst. Growth 174 (1997) 35.