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Al-Fe solid solutions in alloys obtained by melt spinning
Saipta Materialia, Vol. 35, No. 1, pp. 13-16, 1996 Elsevier Science Ltd Copyright 0 1996 Acta Metallurgica Inc. Printed in the. USA. All rights reserved 1359-6462/96 $12.00 + .OO
Pergamon PI1 S1359-6462(96)00089-9
Al-Fe SOLID SOLUTIONS IN ALLOYS OBTAINED BY MELT SPINNING B. Badan, M. Magrini and A. Zambon DIMEG (Dept. of Mechanical and Management Innovation) Universita di Padova, Via Marzolo, 9 - I-35 125 Padova, Italy (Received November 2, 1995) 1. Introduction The extension of solid solutions is one of the more claimed effects of solidification under high cooling rates. The possibility to increase, by such technology, the extremely small amount (0,006 at% at 500°C) of iron in aluminum was extensively studied and recently received further attention, owing to the interesting teclmological properties of Al-Fe alloys. However the rapid quenching from the liquid not only affects the amount of iron retained in solid solution, but al.so the possible formation of other inter-metallic phases, and, more generally, the location of iron atoms retained in the metastable solid solution of aluminum (1). Different situations of iron atoms have been investigated using XRD, TEM and Mijssbauer spectroscopy (MS), but from the interpretation of the results some problems to obtain unambiguous conclusions arise. Perhaps the main discrepancies between the results of various investigations came from the different techniques used in samples preparation and from difficulties in the evaluation of actual cooling rates. In the same range of cooling rates, generally stated between 1E + 06 and 1E + 08 K/s, samples were claimed to be obtained. with fully homogeneous solid solution in thickness as large as 300 urn (2) or on the contrary were homogeneous only if the thickness was below 20 urn (3). Different precipitated phases were revealed by TEM (3,4) but sometimes without appearance of corresponding components in MS spectra (4). Therefore rather different evaluations of the limit of extended solubility of iron are indicated, for instance from $88 to 5-6 at?/o. MS results could be used to clarify a particular situation of iron atoms in aluminum solid solution: association with defects, other atoms, grain boundaries (1). However often different situations correspond to very close hyperfine parameters (h.p.) and unambiguous fit of spectra can be obtained only in alloys with very low iron concentration. In any case it seems interesting to clarify the actual extension of solibility of iron in aluminum, in rather concentrated alloys, in which the formation of metastable intermetallic compounds cannot be suppressed. The paper reports MS analysis of Al-Fe (0,111 at%) alloys, rapidly solidified by melt spinning.
2. Experimental Samples were obtained from high purity (> 99,99) metals, by a melt spinning apparatus operating in argon: copper wheel 130 mm 0 , speed 6000 rpm. The compositions of the alloys were Al-O,1- 1, l- 1,9-3,0-3,9 Fe at??. The thickness of the examined strips was typically 60 urn. The cooling rates were evaluated by 13
Al-Fe SOLID SOLUTIONS
14
Vol. 35, No.
1
0))
(a)
Figure 1. TEM: (a) AI,Fe particles in the matrix (sample Al-Fc l,l at%); (b) AI,Fe particles 3.9 at%)
in an eutectic structure
(sample AI-Fe
Figure 2. (a) Spectra of melt spun 1,1 and 3,9 Fe at% alloys; (b) Spectra of melt spun 3,9 Fe at% alloy annealed at 400°C for 24 h.
TABLE
1
Hyperfine Parameters Used for the Best Fit and Results
_ [mm/s] ‘Solute” iron atoms: ‘Intermetallic”
iron:
(A) single Fe (B) “non cubic” Fe (C) AlsFe (metastable) (D) AIlsFed
(stable)
Allov
I
Fe % at. 0.1
1 1
A = quadrupole simmetry); electron
splitting
6’ (’ referred
(non-zero to a-Fe)
density at the nucleus);
0.290 0.329
[mm/s] 0.425 0.031 0.221
[mm/s] 0.285 0.342 0.285
II:
-0.046 0.174 0.395
0.280 0.280
Relative A 18
1 1
area B 50
1 1
C 32
if iron atoms are at site of non cubic = isomer
r = line width.
shift
(proportional
to the
Al-Fe SOLID SOLUTIONS
Vol. 35, No. 1
15
“0
-r-A&Fe .&6
_._.........__....._.........
_ . .. . . .. . .. . ..
I_........_....._.___.__....._.............................. -...........
Fe In the
alloy (a!%)
Figure 3. Fraction of different form of iron in melt-spun alloys versus the total amount of iron in the alloy.
a finite differences computer simulation, with the maximum value on the wheel side of 1E + 07 K/s and the minimum on the opposite side of 1E + 05 K/s. Miissabauer measurements were obtained by a conventional spectrometer.
3. Results and Discussion TEM microscopy performed on the samples allowed to reveal on all of them the presence of some precipitated phases. In the samples with higher iron content (1,9-3-3,9) particles of metastable A&Fe were identified, about 100 nm in diameter, and for the highest iron content also an eutectic structure (Fig. 1). Mijssbauer spectra, (examples in Fig. 2), could be conveniently fitted using three components, whose h.p. are listed in Table 1. The single and the (c) doublet correspond respectively to single iron in aluminum and to the metastable A&Fe. For the (b) doublet the best fit h.p. seem to correspond to those attributed (1) to iron atoms at “grain boundaries location”. However it seems more correct and realistic to attribute this component more generally to iron atoms still in solid solution, but in situation of non cubic symmetry: between the two the more frequent could be the “grain boundaries location”. The relative areas of the three components are indicated in Table 1, and were plotted versus the total iron content in Fig. 3. This figure shows that, as expected, the intermetallic A&Fe became soon the main form of iron present in the alloys, continuously increasing with the total Fe amount. Instead other forms of iron atoms still remaining in solid solution, reach a value which remain almost constant, for iron content over 3 at%. This behaviour appe;ars rather reasonable: it depicts the limit for the possibility for iron atoms to remain in metastable solid solution in aluminum, in competition with the precipitation of particles of intermetallic A&Fe. For our samples the extension of solid solution of iron in aluminum reaches the limit of about 1 at%. This result agrees with the value reported (4) for samples obtained with a different quenching technique, but with similar precipitation observed by TEM. The remarkable differences with higher extensions of solid solution previously mentioned can be justified taking in account that such higher limits have been obtained only in samples where any other precipitation (A&Fe or other intermetallics) was suppressed. Clearly this result can be achieved only by using very high cooling rates in sample preparation. Therefore it seems necessary to conclude that, as to be expected, the rate of extension of solid solution of iron in aluminum is markedly affected by the cooling rate and can be largely enhanced only if the sample preparation technique and sample thickness allow to completely avoid the precipitation of intermetailics. If some precipitation of A&Fe occurs, the extension of solid solution can reach about 1 at%. The annealing of samples produce the transformation of metastable A&Fe into the stable intermetallic Al,,Fe, (A&Fe), see spectra in Fig. 2, as previously observed (6).
16
Al-Fe SOLID SOLUTIONS
Vol. 35, No. 1
References 1. 2. 3. 4. 5. 6. 7. 8.
S. Nasu, U. Gonser, R.S. Preston, J. Phys. Cl, 41 (1980) 385. S. Nasu, U. Gonser, P.H. Shingu, Y. Murakami, J. Phys. F, 4 (1974) 124. E. Blank, 2. Metallk., 63 (1972) 315. H. Ichinose, H. Ito, Proc. Conj Rapidly Quenched Metals, S. Steeb, H. Warlimont, Editors, (1985) Elsevier Science Pub. H. Jones, Aluminum, 54 (1978) 274. B. Badan, M. Magrini, E. Ramous, Ser. Met., 23,212l (1989). W.J. Boettiger, Mat. Sci. Eng., 98 (1988) 123. M.G. Chu, D.A. Granger, Metall. Trans. ,21A, (1990) 205.
Pergamon PI1 S1359-6462(96)00089-9
Al-Fe SOLID SOLUTIONS IN ALLOYS OBTAINED BY MELT SPINNING B. Badan, M. Magrini and A. Zambon DIMEG (Dept. of Mechanical and Management Innovation) Universita di Padova, Via Marzolo, 9 - I-35 125 Padova, Italy (Received November 2, 1995) 1. Introduction The extension of solid solutions is one of the more claimed effects of solidification under high cooling rates. The possibility to increase, by such technology, the extremely small amount (0,006 at% at 500°C) of iron in aluminum was extensively studied and recently received further attention, owing to the interesting teclmological properties of Al-Fe alloys. However the rapid quenching from the liquid not only affects the amount of iron retained in solid solution, but al.so the possible formation of other inter-metallic phases, and, more generally, the location of iron atoms retained in the metastable solid solution of aluminum (1). Different situations of iron atoms have been investigated using XRD, TEM and Mijssbauer spectroscopy (MS), but from the interpretation of the results some problems to obtain unambiguous conclusions arise. Perhaps the main discrepancies between the results of various investigations came from the different techniques used in samples preparation and from difficulties in the evaluation of actual cooling rates. In the same range of cooling rates, generally stated between 1E + 06 and 1E + 08 K/s, samples were claimed to be obtained. with fully homogeneous solid solution in thickness as large as 300 urn (2) or on the contrary were homogeneous only if the thickness was below 20 urn (3). Different precipitated phases were revealed by TEM (3,4) but sometimes without appearance of corresponding components in MS spectra (4). Therefore rather different evaluations of the limit of extended solubility of iron are indicated, for instance from $88 to 5-6 at?/o. MS results could be used to clarify a particular situation of iron atoms in aluminum solid solution: association with defects, other atoms, grain boundaries (1). However often different situations correspond to very close hyperfine parameters (h.p.) and unambiguous fit of spectra can be obtained only in alloys with very low iron concentration. In any case it seems interesting to clarify the actual extension of solibility of iron in aluminum, in rather concentrated alloys, in which the formation of metastable intermetallic compounds cannot be suppressed. The paper reports MS analysis of Al-Fe (0,111 at%) alloys, rapidly solidified by melt spinning.
2. Experimental Samples were obtained from high purity (> 99,99) metals, by a melt spinning apparatus operating in argon: copper wheel 130 mm 0 , speed 6000 rpm. The compositions of the alloys were Al-O,1- 1, l- 1,9-3,0-3,9 Fe at??. The thickness of the examined strips was typically 60 urn. The cooling rates were evaluated by 13
Al-Fe SOLID SOLUTIONS
14
Vol. 35, No.
1
0))
(a)
Figure 1. TEM: (a) AI,Fe particles in the matrix (sample Al-Fc l,l at%); (b) AI,Fe particles 3.9 at%)
in an eutectic structure
(sample AI-Fe
Figure 2. (a) Spectra of melt spun 1,1 and 3,9 Fe at% alloys; (b) Spectra of melt spun 3,9 Fe at% alloy annealed at 400°C for 24 h.
TABLE
1
Hyperfine Parameters Used for the Best Fit and Results
_ [mm/s] ‘Solute” iron atoms: ‘Intermetallic”
iron:
(A) single Fe (B) “non cubic” Fe (C) AlsFe (metastable) (D) AIlsFed
(stable)
Allov
I
Fe % at. 0.1
1 1
A = quadrupole simmetry); electron
splitting
6’ (’ referred
(non-zero to a-Fe)
density at the nucleus);
0.290 0.329
[mm/s] 0.425 0.031 0.221
[mm/s] 0.285 0.342 0.285
II:
-0.046 0.174 0.395
0.280 0.280
Relative A 18
1 1
area B 50
1 1
C 32
if iron atoms are at site of non cubic = isomer
r = line width.
shift
(proportional
to the
Al-Fe SOLID SOLUTIONS
Vol. 35, No. 1
15
“0
-r-A&Fe .&6
_._.........__....._.........
_ . .. . . .. . .. . ..
I_........_....._.___.__....._.............................. -...........
Fe In the
alloy (a!%)
Figure 3. Fraction of different form of iron in melt-spun alloys versus the total amount of iron in the alloy.
a finite differences computer simulation, with the maximum value on the wheel side of 1E + 07 K/s and the minimum on the opposite side of 1E + 05 K/s. Miissabauer measurements were obtained by a conventional spectrometer.
3. Results and Discussion TEM microscopy performed on the samples allowed to reveal on all of them the presence of some precipitated phases. In the samples with higher iron content (1,9-3-3,9) particles of metastable A&Fe were identified, about 100 nm in diameter, and for the highest iron content also an eutectic structure (Fig. 1). Mijssbauer spectra, (examples in Fig. 2), could be conveniently fitted using three components, whose h.p. are listed in Table 1. The single and the (c) doublet correspond respectively to single iron in aluminum and to the metastable A&Fe. For the (b) doublet the best fit h.p. seem to correspond to those attributed (1) to iron atoms at “grain boundaries location”. However it seems more correct and realistic to attribute this component more generally to iron atoms still in solid solution, but in situation of non cubic symmetry: between the two the more frequent could be the “grain boundaries location”. The relative areas of the three components are indicated in Table 1, and were plotted versus the total iron content in Fig. 3. This figure shows that, as expected, the intermetallic A&Fe became soon the main form of iron present in the alloys, continuously increasing with the total Fe amount. Instead other forms of iron atoms still remaining in solid solution, reach a value which remain almost constant, for iron content over 3 at%. This behaviour appe;ars rather reasonable: it depicts the limit for the possibility for iron atoms to remain in metastable solid solution in aluminum, in competition with the precipitation of particles of intermetallic A&Fe. For our samples the extension of solid solution of iron in aluminum reaches the limit of about 1 at%. This result agrees with the value reported (4) for samples obtained with a different quenching technique, but with similar precipitation observed by TEM. The remarkable differences with higher extensions of solid solution previously mentioned can be justified taking in account that such higher limits have been obtained only in samples where any other precipitation (A&Fe or other intermetallics) was suppressed. Clearly this result can be achieved only by using very high cooling rates in sample preparation. Therefore it seems necessary to conclude that, as to be expected, the rate of extension of solid solution of iron in aluminum is markedly affected by the cooling rate and can be largely enhanced only if the sample preparation technique and sample thickness allow to completely avoid the precipitation of intermetailics. If some precipitation of A&Fe occurs, the extension of solid solution can reach about 1 at%. The annealing of samples produce the transformation of metastable A&Fe into the stable intermetallic Al,,Fe, (A&Fe), see spectra in Fig. 2, as previously observed (6).
16
Al-Fe SOLID SOLUTIONS
Vol. 35, No. 1
References 1. 2. 3. 4. 5. 6. 7. 8.
S. Nasu, U. Gonser, R.S. Preston, J. Phys. Cl, 41 (1980) 385. S. Nasu, U. Gonser, P.H. Shingu, Y. Murakami, J. Phys. F, 4 (1974) 124. E. Blank, 2. Metallk., 63 (1972) 315. H. Ichinose, H. Ito, Proc. Conj Rapidly Quenched Metals, S. Steeb, H. Warlimont, Editors, (1985) Elsevier Science Pub. H. Jones, Aluminum, 54 (1978) 274. B. Badan, M. Magrini, E. Ramous, Ser. Met., 23,212l (1989). W.J. Boettiger, Mat. Sci. Eng., 98 (1988) 123. M.G. Chu, D.A. Granger, Metall. Trans. ,21A, (1990) 205.