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Solid solubility of rare earths in aluminium
Journal of the Less-Common
SOLID SOLUBILITY A. CHELKOWSKI, A. WINIARSKI
Institute (Received
of Physics, November
Metals,
141 (1988)
213 - 216
OF RARE EARTHS
E. TALIK,
J. SZADE,
Silesian University,
213
IN ALUMINIUM
J. HEIMANN,
Uniwersytecka
A. WINIARSKA
and
4, 40-007 Katowice
(Poland)
25, 1987)
Summary Monocrystalline and polycrystalline samples of Al:R (R=Y, Gd, Tb, Dy, Er, Ho) were prepared by arc and levitation melting and the Czochralski method from the levitated melt, It follows from the electrical and magnetic measurements as well as the X-ray examinations that the equilibrium solid solubility is less than 100 ppm. The residual resistivity has a maximum at about 150 ppm and then decreases dramatically with increasing concentration. This is explained by nucleation of the RAI, phase.
1. Introduction There is no detailed information about rare earth impurities in aluminium. Reliable data about the solubility of rare earths are not available except for the Al: SC system [ 1, 21. The existing data concerning the solubility of the rare earths in aluminium are only roughly estimated [3]. Rettori et al. [4] observed with an electron microprobe that rare earths were not homogeneously distributed in aluminium and 2 pm diameter spots existed. The composition of the spots was not determined. The aim of this paper was to determine the distribution of rare earth impurities in single crystals and polycrystalline samples obtained by various crucibleless methods.
2. Experimental
details
2.1. Sample preparation and X-ray real strut ture examination The samples Al:R (R=Y, Gd, Tb, Dy, Ho and Er) with concentrations of 50 - 12 000 ppm of rare earth were prepared by (A) arc melting (erbium, dysprosium), (B) levitation melting (yttrium, gadolinium, terbium, holmium, erbium) and (C) the Czochralski method from the levitating melt [5 3 (yttrium, gadolinium, dysprosium, erbium). 0022s5088/88/$3.50
0 Elsevier
Sequoia/Printed
in The Netherlands
214
The starting materials were 99.999% Al and 99.9% R. The master samples in the A method were prepared with a rare earth concentration of about 1 at.%. Each sample (100 - 200 mg) was remelted several times. The samples (500 - 1500 mg) prepared by the B and C methods were obtained from aluminium rod with rare earth kneaded inside and remelted several times. The real structure of the samples obtained by the B and C methods was examined by chemical etching, Laue, Berg-Barrett and Lang methods. The samples were single crystals or they consisted of several longitudinal grains of size comparable with the length of the sample. Real structure examination revealed decreasing mosaic block dimensions and the increasing misorientation angles with increasing concentration. For the smallest concentrations only a few low angle boundaries were observed. The Berg-Barrett topography did not reveal any precipitation. The same single crystals examined by the Laue method showed not only the Laue spots but also the Debye-Scherrer lines. The dimensions of the precipitates were estimated from these lines to be less than 1 pm. The Lang topography of the sample with 50 ppm Y did not exhibit any precipitation beyond the resolution capability (2 pm). The samples with 2000 ppm Gd consisted of mosaic blocks of dimensions about 2 mm. For higher concentrations (5000 ppm) the samples were polycrystalline with small grains (size less than 1 mm). 2.2. Magnetic susceptibility measurements The magnetic susceptibility of spherical samples was measured using the Faraday method in fields of 0.15 - 0.32 T over the temperature range 1.54 300 K under an atmosphere of helium. The molar susceptibility of the rare earths was obtained by subtracting the experimental susceptibility of pure aluminium from the susceptibility of the alloy. It was checked that the susceptibilities of the different parts of the sample had the same value. The NCel and paramagnetic temperatures and effective magnetic moments were estimated for the concentrations above 500 ppm. The samples with lower concentrations did not exhibit CurieWeiss behaviour. The results of the magnetic measurements for Al:Er and Al:Dy are collected in Table 1. 2.3. Electrical resistivity measurements The electrical resistivities of the samples prepared by the B and C methods were measured by the conventional method using a 100 - 500 mA direct current. The samples for the electrical measurements were cut in the form of a rectangular prism (about 1 mm X 1 mm X 6 mm) by a wire saw. The temperature dependence of the electrical resistivity was measured in the range 4.2 - 300 K. Next, the samples were annealed in vacuum in a molybdenum container at 870 K for 20 h and then quenched in water. The electrical resistivity measurements then were obtained again.
215 TABLE
1
The paramagnetic
and Nobel temperatures
Concentration
of Al:Er
Temperature
(ppm)
and Al:Dy
(K)
Paramagnetic
Nkel
Erbium 11190 5218 1848 862 478
Dysprosium 12160 5852 2342 1215 529
-23 z-18 z-15 -15 e-15
6 6 66 =6
-46 -41 -39 -35 -15
30 = 33 = 33 30 27
3. Results and discussion The residual resistivity us. concentration (Fig. 1) exhibits increasing p&c) up to about 150 ppm. Above this value the dependence shows a sharp decrease. From concentrations of about 300 ppm the residual resistivity is almost independent of concentration. The residual resistivity of the annealed samples is unchanged. For the samples with concentrations above 150 ppm a small decrease in the residual resistivity is observed after annealing. The paramagnetic and NCel temperatures (Table 1) for the samples rich in rare earth are close to the RAl, values (ref. 6). The Laue patterns of the samples with concentrations of 200 ppm and higher show, in addition to the monocrystalline Laue spots, the weak RAl, Debye-Scherrer lines. From the results of the electrical measurements one can conclude that in the samples with concentrations above about 150 ppm precipitation
(a)
Concentration
of Er [ppm]
Fig. 1. The concentration dependence 870 K) for (a) Al:Er and (b) Al:Y.
@I
of the residual
Concentration
resistivity
after
of Y
[ppm]
annealing
(20
h at
216
occurs. The paramagnetic and Neel temperatures for the concentrations above 400 ppm suggest the formation of RAl,. This was proved by X-ray methods. It seems that, contrary to the Al:Sc system [l, 21, the maximum residual resistivity concentration is not the equilibrium concentration which can be inferred from the decrease in the residual resistivity with increasing concentration. This can be explained by nucleation. While nuclei of the new phase are not being created, the supersaturation of the rare earth solid solution takes place. The greater number of nuclei causes the capture of rare earth atoms. The concentration approaches the equilibrium concentration, the residual resistivity subsequently decreasing. Similarly to results of Rettori et al. [ 41, the crystallites of the new phase are about 1 E.trnin size.
Acknowledgment This work was supported by the Polish Academy of Sciences under Project CPBP 01.20.3.
References 1 S. Fujikawa, M. Sugaya, H. Takei and K. Hirano, J. Less-Common Met., 63 (1979) 87. 2 M. Ocko, E. Babic, R. Krsmik, E. Girt and B. Leontic, J. Phys. F, 6 (1976) 703. 3 E. M. Savicky and A. W. Tieriechowa, Metallowiedienie Riedkoziemielnych Metallov, Nauka, Moscow, 1975. 4 C. Rettori, D. Davidov, R. Orbach, P. Chock and B. Ricks, Phys. Rev. B, 7 (1973) 1. 5 E. Talik, J. Szade, J. Heimann, A. Winiarska, A. Winiarski and A. Che&owski, J. LessCommon Met., 138 (1988) 129. 6 K. H. J. Buschow, Rep. Prog. Phys., 42 (1979) 1374.
SOLID SOLUBILITY A. CHELKOWSKI, A. WINIARSKI
Institute (Received
of Physics, November
Metals,
141 (1988)
213 - 216
OF RARE EARTHS
E. TALIK,
J. SZADE,
Silesian University,
213
IN ALUMINIUM
J. HEIMANN,
Uniwersytecka
A. WINIARSKA
and
4, 40-007 Katowice
(Poland)
25, 1987)
Summary Monocrystalline and polycrystalline samples of Al:R (R=Y, Gd, Tb, Dy, Er, Ho) were prepared by arc and levitation melting and the Czochralski method from the levitated melt, It follows from the electrical and magnetic measurements as well as the X-ray examinations that the equilibrium solid solubility is less than 100 ppm. The residual resistivity has a maximum at about 150 ppm and then decreases dramatically with increasing concentration. This is explained by nucleation of the RAI, phase.
1. Introduction There is no detailed information about rare earth impurities in aluminium. Reliable data about the solubility of rare earths are not available except for the Al: SC system [ 1, 21. The existing data concerning the solubility of the rare earths in aluminium are only roughly estimated [3]. Rettori et al. [4] observed with an electron microprobe that rare earths were not homogeneously distributed in aluminium and 2 pm diameter spots existed. The composition of the spots was not determined. The aim of this paper was to determine the distribution of rare earth impurities in single crystals and polycrystalline samples obtained by various crucibleless methods.
2. Experimental
details
2.1. Sample preparation and X-ray real strut ture examination The samples Al:R (R=Y, Gd, Tb, Dy, Ho and Er) with concentrations of 50 - 12 000 ppm of rare earth were prepared by (A) arc melting (erbium, dysprosium), (B) levitation melting (yttrium, gadolinium, terbium, holmium, erbium) and (C) the Czochralski method from the levitating melt [5 3 (yttrium, gadolinium, dysprosium, erbium). 0022s5088/88/$3.50
0 Elsevier
Sequoia/Printed
in The Netherlands
214
The starting materials were 99.999% Al and 99.9% R. The master samples in the A method were prepared with a rare earth concentration of about 1 at.%. Each sample (100 - 200 mg) was remelted several times. The samples (500 - 1500 mg) prepared by the B and C methods were obtained from aluminium rod with rare earth kneaded inside and remelted several times. The real structure of the samples obtained by the B and C methods was examined by chemical etching, Laue, Berg-Barrett and Lang methods. The samples were single crystals or they consisted of several longitudinal grains of size comparable with the length of the sample. Real structure examination revealed decreasing mosaic block dimensions and the increasing misorientation angles with increasing concentration. For the smallest concentrations only a few low angle boundaries were observed. The Berg-Barrett topography did not reveal any precipitation. The same single crystals examined by the Laue method showed not only the Laue spots but also the Debye-Scherrer lines. The dimensions of the precipitates were estimated from these lines to be less than 1 pm. The Lang topography of the sample with 50 ppm Y did not exhibit any precipitation beyond the resolution capability (2 pm). The samples with 2000 ppm Gd consisted of mosaic blocks of dimensions about 2 mm. For higher concentrations (5000 ppm) the samples were polycrystalline with small grains (size less than 1 mm). 2.2. Magnetic susceptibility measurements The magnetic susceptibility of spherical samples was measured using the Faraday method in fields of 0.15 - 0.32 T over the temperature range 1.54 300 K under an atmosphere of helium. The molar susceptibility of the rare earths was obtained by subtracting the experimental susceptibility of pure aluminium from the susceptibility of the alloy. It was checked that the susceptibilities of the different parts of the sample had the same value. The NCel and paramagnetic temperatures and effective magnetic moments were estimated for the concentrations above 500 ppm. The samples with lower concentrations did not exhibit CurieWeiss behaviour. The results of the magnetic measurements for Al:Er and Al:Dy are collected in Table 1. 2.3. Electrical resistivity measurements The electrical resistivities of the samples prepared by the B and C methods were measured by the conventional method using a 100 - 500 mA direct current. The samples for the electrical measurements were cut in the form of a rectangular prism (about 1 mm X 1 mm X 6 mm) by a wire saw. The temperature dependence of the electrical resistivity was measured in the range 4.2 - 300 K. Next, the samples were annealed in vacuum in a molybdenum container at 870 K for 20 h and then quenched in water. The electrical resistivity measurements then were obtained again.
215 TABLE
1
The paramagnetic
and Nobel temperatures
Concentration
of Al:Er
Temperature
(ppm)
and Al:Dy
(K)
Paramagnetic
Nkel
Erbium 11190 5218 1848 862 478
Dysprosium 12160 5852 2342 1215 529
-23 z-18 z-15 -15 e-15
6 6 66 =6
-46 -41 -39 -35 -15
30 = 33 = 33 30 27
3. Results and discussion The residual resistivity us. concentration (Fig. 1) exhibits increasing p&c) up to about 150 ppm. Above this value the dependence shows a sharp decrease. From concentrations of about 300 ppm the residual resistivity is almost independent of concentration. The residual resistivity of the annealed samples is unchanged. For the samples with concentrations above 150 ppm a small decrease in the residual resistivity is observed after annealing. The paramagnetic and NCel temperatures (Table 1) for the samples rich in rare earth are close to the RAl, values (ref. 6). The Laue patterns of the samples with concentrations of 200 ppm and higher show, in addition to the monocrystalline Laue spots, the weak RAl, Debye-Scherrer lines. From the results of the electrical measurements one can conclude that in the samples with concentrations above about 150 ppm precipitation
(a)
Concentration
of Er [ppm]
Fig. 1. The concentration dependence 870 K) for (a) Al:Er and (b) Al:Y.
@I
of the residual
Concentration
resistivity
after
of Y
[ppm]
annealing
(20
h at
216
occurs. The paramagnetic and Neel temperatures for the concentrations above 400 ppm suggest the formation of RAl,. This was proved by X-ray methods. It seems that, contrary to the Al:Sc system [l, 21, the maximum residual resistivity concentration is not the equilibrium concentration which can be inferred from the decrease in the residual resistivity with increasing concentration. This can be explained by nucleation. While nuclei of the new phase are not being created, the supersaturation of the rare earth solid solution takes place. The greater number of nuclei causes the capture of rare earth atoms. The concentration approaches the equilibrium concentration, the residual resistivity subsequently decreasing. Similarly to results of Rettori et al. [ 41, the crystallites of the new phase are about 1 E.trnin size.
Acknowledgment This work was supported by the Polish Academy of Sciences under Project CPBP 01.20.3.
References 1 S. Fujikawa, M. Sugaya, H. Takei and K. Hirano, J. Less-Common Met., 63 (1979) 87. 2 M. Ocko, E. Babic, R. Krsmik, E. Girt and B. Leontic, J. Phys. F, 6 (1976) 703. 3 E. M. Savicky and A. W. Tieriechowa, Metallowiedienie Riedkoziemielnych Metallov, Nauka, Moscow, 1975. 4 C. Rettori, D. Davidov, R. Orbach, P. Chock and B. Ricks, Phys. Rev. B, 7 (1973) 1. 5 E. Talik, J. Szade, J. Heimann, A. Winiarska, A. Winiarski and A. Che&owski, J. LessCommon Met., 138 (1988) 129. 6 K. H. J. Buschow, Rep. Prog. Phys., 42 (1979) 1374.