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Influence of superconducting transition on low temperature jump-like deformation of metals and alloys
ELSEVIER
Materials Science and Engineering A234-236 (1997) 157- 160
Influence of superconducting transition on low temperature jump-like deformation of metals and alloys V.V. Pustovalov B. Verkin
Institute
for
Low
Temperature
Physics
*
and Engineering, National Academy Kharkov 310164, Ukraine
of Sciences
of Ukraine,
Lenin?
Avenue
47,
Received 23 January 1997; received in revised form 27 March 1997
Abstract Systemized results on the influence of the deformation are presented for a number of pure superconducting state the jump-like deformation is discussed in terms of current concepts of the Keywords:
superconducting transition upon the macroscopic low temperature jump-like metals and alloys. In all cases qualitatively similar results were observed-in the is either absent or underdeveloped as compared to the normal state. This finding nature of low temperature instability. 0 1997 Elsevier Science S.A.
Jump like deformation; Superconducting transition
1. Introduction Plastic deformation of most metals and alloys becomes macroscopically unstable as temperature decreases: the stress-strain curve exhibits jumps in the flow stress. Low temperature jump-like deformation (LTJD) has been a subject of numerous experimental and theoretical studies since the discovery of the phenomenon in 1956 [1,2]. One of the hypotheses assumes that the low temperature jumps are caused by thermomechanical instability. The main evidence in favor of this interpretation comes from the recorded temperature spikes occurring during a jump. Several pioneering studies have taken place [3-91. Another hypothesis assumesthat at low temperature deformation proceeds with a hampered cross slip and as a result accumulations of dislocations pile-up and a break through them at high local stressescausesstressjumps [lo]. There are sufficient experimental arguments to back this hypothesis and their number has increased recently. To advance the understanding of the nature and particular mechanisms of LTJD, new experiments are required which would ensure controllable changes in the sample deformed. In this context it is important to perform measurement on a sample undergoing superconducting * Tel: + 7 380 572300331; fax: + 7 380 572322370; e-mail: [email protected] 0921-5093/97/$17.00 0 1997 Elsevier Science S.A. All rights reserved. PIZSO921-5093(97)00151-2
transition during the process of deformation. For some time this obvious idea could not be realized because of technical problems. The advent of new deformation facilities [ll] has permitted the extension of the temperature range down to 0.4 K and has thus made the required experiments possible. Consideration of the observed regularities and their comparison with current hypotheses are presented in this study.
2. Initial experiments It appears likely that the problem of the influence of the superconducting transition on jump-like deformation was, for the first time, approached in the study on niobium single crystals [4]. At 2.17 K appreciable difference appeared between the stresses of the onset of jump-like deformation. In the normal state jumps occurred earlier (roN = 165 MPa) than in the superconducting state (zos = 208 MPa). The result at 4.2 k was less distinct. The fact that the experiment was performed on two samples reduces the reliability of the results. The experiment studying the N-S transition influence on the deforming stress of Pb and its alloys [12] revealed appreciable deviations in the character of deformation. The superconducting transition either led to the disappearance of jumps or considerably decreased
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/Materials
Science
and Engineering
their amplitude. Systematic investigations are required to clear up the general regularities of the influence produced by the superconducting transition.
3. Experimental technique Superconductors which exhibited jump-like deformation below 4.2 K were investigated, including pure metals (Al, Pb, In) and alloys (In-Pb, Al-Mg, Al-Mn, Al-Li) at several concentrations. Both single and polycrystals were subjected to tension and compression at a constant strain rate (10 - 4- 10- 5 s ~ ‘) in the temperature range 4.2-0.5 K using an original unit [ll] and a three-step cooling system with liquid nitrogen, helium-4 and helium-3.
4. Results 4.1. Pure metals The samples were aluminium (99.5%) [13] polycrystals in which LTJD is well developed. The S-N and N-S transitions were achieved by switching on and off the magnetic field of H N 150 mT. Jump-like deformation first appears only in the N-state. In the N-S transition, the jumps disappear. In the S-state jumps were observed immediately before the sample fracture. A qualitatively similar result was obtained on deforming identical samplesat the sametemperature, - 0.8 K, but the samples were in different states. Next, we wanted to find out to what extent this behaviour is typical. Pb (99.997%) polycrystals were deformed under tension and compression [14]. Macroscopic jumps appeared below 1 K. Jump-like deformation is typically observed in the N-state and is enhanced when the temperature decreases.Thorough studies were also performed on In single crystals [15]. The axis of compression runs halfway between the directions [loo] and [l lo]. The experiments with periodically alternating states show that the character of jump-like deformation is dependent on the degree of deformation and the state of the sample. The first jump appears in the N-state. Their frequency increaseswith deformation. Individual jumps are observed in the S-state too. Later on deformation is jump-like both in the N- and S-states but the jump amplitudes are about 2.5 times larger in the N-state.
A234-236
(1997)
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jumps can be observed only in the N-state, with the transition of the sample to the S-state they completely disappear. As deformation increases, jumps start appearing in the S-state as well. Their amplitudes and frequency increase with deformation reaching, at a certain stage, the amplitudes and frequency of the N-state. In Al-Li alloys jump-like deformation occurs at 4.2 K and below. The following principal regularities of jump-like deformation have been found for quenched Al-Li alloys of three concentrations (3.8, 7.0 and 10.4 at.% Li). At higher impurity concentrations it develops in smaller degrees of deformation and the frequency and amplitudes of jumps increase. A similar effect is observed with decreasing temperature. At constant temperatures and Li concentrations the amplitudes and frequency of jumps increase gradually with deformation and the intervals between them decrease. The influence of the electronic state of the sampleson jump-like deformations is illustrated in Fig. 2. A change to the S-state either terminates jump-like deformation (at low deformation) or makes it appreciably weaker (moderate deformation). At a certain degree of deformation the N-S transition does not influence the character of plastic flow, just like in Al-Mg alloys.
Al-1,85%Mg i.i,f4d’C”
S
4.2. Alloys The results for alloys qualitatively agree with those for pure metals. Fig. 1 shows some portions of the stress-strain curves taken on Al-O.85 at.% Mg polycrystals under tension. At the beginning of deformation
Fig. 1. Portion of tensile stress-strain curve taken on the Al-l.85 at.O% Mg polycrystal with a change in the electronic state of the sample during deformation. T=0.5 K, e= 1.1.10V5 SC’ [16].
V. V. Pustovalov
/Materials
Science
and Engineering
E=0.0%
E - 3.4%
PP S
N
S N
s
s
m
RI
“s “! I 0-
!i “! I 0-
0.1%
0.1%
E = 29%
E-21% N
S
S P GJ
11 d - 0.1%
Q
f
41
1%
--
Fig. 2. Portions of the tensile stress-strain curve illustrating the influencing of the N-S transition upon jump-like deformation: Al-3.8 at.% Li, T=O.S K, Z:= lop5 ssi [17].
5. Discussion The studies of jump-like deformation in normal, superconducting states and in the process of N =+=S, S *N transitions show that in the superconducting state macroscopic jump-like deformation is as a rule less developed or absent. This effect of N-S transition may be considered typical. In terms of concepts which treat the low temperature jump-like deformation as a manifestation of thermomechanical instability, the stress of the jump-like deformation onset r, at constant temperature and deformation rate is generally dependent on three physical parameters-thermal conductivity coefficient K, heat capacity C, and surface heat transfer coefficient h [4-91. Of these, h is independent of the electronic state, C varies appreciable only near T,, being C, N C, in all other cases. This means that z, can change only with K. We have knowledge of K about some of them-Al, Pb, Sn, where KS < KN. According to the mechanism of thermomechanical instability, r, should decrease during the N-S transition, i.e. jumplike deformation is expected to be enhanced. Experiments show the reverse effect. To explain the
A234-236
(1997)
157-160
159
discrepancy observed, a modified theory was proposed which allowed for the temperature dependence of the flow stress [18,19]. Within this theoretical model, the N-S transition can influence jump-like deformation in different ways. The type of influence depends on the sign of dz/dT and its change in the process of the N-S transition. The data available about the temperature dependencies of zO, go, z,,,, g,,, [13- 181 show that different dependencies s(T) are observed, and the sign of dz/dT either does not change (dz/dT > 0, dz/dT < 0) or (dr/dT = 0) in a very narrow interval near T,. The influence of the N-S transition on jump-like deformation is the same irrespective of all 7(T) and dz/dT variations. It is a change in the dependence z(T) that can cause extinction of jump-like deformation in the superconducting state. Let us compare these regularities with the dynamic dislocation hypothesis [lo]. Proceeding from current concepts of dislocation motion in the normal and superconducting states [1,2], we can explain the influence of the N-S transition on jump-like deformation. Against the N-state, some obstacles in the S-state can be overcome due to the inertial effects. The jumps will appear later on and their amplitudes will be smaller under the same deformation. With any z(T), the process may be seen as single jumps or a serrated curve. Within this model the process of jump-like deformation does not require r to decrease with increasing temperature. The absence of any influence of the N-S transition upon jump-like deformation under high stresses in high-strength Al alloys is most likely due to weak heating (0.5-1.2 K) of the sample and its switching over to the normal state. The results from the influence of the superconducting transition upon jumplike deformation favor of the dynamic hypothesis.
References 111V.I.
Startsev, V.Y. Il’itchev and V.V. Pustovalov, Plasticity and Strength of Metals and Alloys at Low Temperatures, Metallurgia, Moscow, 1975, p. 325 (in Russian). (Ed.), Dislocation in Solids, PI V.I. Startsev, in: F.R.N. Nabarro Vol. 6, North Holland, Amsterdam, 1983, p. 145. Proc. R. Sot. London, Ser. A 240 (1957) 229. 131 Z.S. Basinski, B. Jouffrey, Phil. Mag. 24 (N188) (1971) 437. 141 L.P. Kubin, S. Takeuchi, T. Suzuki, J. Phys. Sot. Jpn. 34 (N5) 151E. Kuramoto, (1973) 1217. 161G.A. Malygin, Phys. Stat. Sol. (b) 61 (1974) K45. Yu.Z. Estrin, Sov. Phys. Solid State 17 (N7) [71 B.V. Petukhov, (1975) 1333. 181Yu.Z. Estrin, L.P. Kubin, Ser. Metall. 14 (N12) (1980) 1359. I.N. Nechiporenko, Sov. J. Low Temp. Phys. 4 [91 IS. Zhitomirski, (NS) (1978) 499. 1101A. Seeger, in: J.C. Fisher, W.G. Johnston, K. Thomson, T. Vreeland (Eds.), Dislocation and Mechanical Properties of Crystals, Wiley, New York, 1957. V.S. Fomenko, Y.I. Gofman, Preprint FTINT 1111V.V. Pustovalov, AN Ukr. SSR, 6 October 1972, Kharkov, p. 17 (in Russian).
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/Materials
Science
and Engineering
[12] T.A. Parkhomenko, IN. Kuzmenko, V.V. Pustovalov, Sov. Low Temp. Phys. 4 (NlO) (1978) 632. [13] I.N. Kuzmenko, V.V. Pustovalov, Sov. J. Low Temp. Phys. 5 (N12) (1979) 679. [14] I.N. Kuzmenko, V.V. Pustovalov, Sov. Phys. Doklady, 44 (1985) 50 (English translation). [15] I.N. Kuzmenko, S.V. Lubenets, V.V. Pustovalov, S.E. Shumilin,
A234-236
(1997)
157-160
Sov. J. Low Temp. Phys. 9 (N8) (1983) 450. [16] V.V. Pustovalov, S.E. Shumilin, Sov. Phys. Phys. Metal. Metallogr. 52 (Nl) (1986) 57. [17] N.V. Isaev, V.V. Pustovalov, V.S. Forenko, S.E. Shumilin, Low Temp. Phys. 20 (N8) (1994) 653. [18] G.A. Malygin, Sov. J. Low Temp. Phys. 12 (N8) (1986) 481. [19] I.N. Nechiporenko, Sov. J. Low Temp. Phys. 12 (Nl) (1986) 43.
Materials Science and Engineering A234-236 (1997) 157- 160
Influence of superconducting transition on low temperature jump-like deformation of metals and alloys V.V. Pustovalov B. Verkin
Institute
for
Low
Temperature
Physics
*
and Engineering, National Academy Kharkov 310164, Ukraine
of Sciences
of Ukraine,
Lenin?
Avenue
47,
Received 23 January 1997; received in revised form 27 March 1997
Abstract Systemized results on the influence of the deformation are presented for a number of pure superconducting state the jump-like deformation is discussed in terms of current concepts of the Keywords:
superconducting transition upon the macroscopic low temperature jump-like metals and alloys. In all cases qualitatively similar results were observed-in the is either absent or underdeveloped as compared to the normal state. This finding nature of low temperature instability. 0 1997 Elsevier Science S.A.
Jump like deformation; Superconducting transition
1. Introduction Plastic deformation of most metals and alloys becomes macroscopically unstable as temperature decreases: the stress-strain curve exhibits jumps in the flow stress. Low temperature jump-like deformation (LTJD) has been a subject of numerous experimental and theoretical studies since the discovery of the phenomenon in 1956 [1,2]. One of the hypotheses assumes that the low temperature jumps are caused by thermomechanical instability. The main evidence in favor of this interpretation comes from the recorded temperature spikes occurring during a jump. Several pioneering studies have taken place [3-91. Another hypothesis assumesthat at low temperature deformation proceeds with a hampered cross slip and as a result accumulations of dislocations pile-up and a break through them at high local stressescausesstressjumps [lo]. There are sufficient experimental arguments to back this hypothesis and their number has increased recently. To advance the understanding of the nature and particular mechanisms of LTJD, new experiments are required which would ensure controllable changes in the sample deformed. In this context it is important to perform measurement on a sample undergoing superconducting * Tel: + 7 380 572300331; fax: + 7 380 572322370; e-mail: [email protected] 0921-5093/97/$17.00 0 1997 Elsevier Science S.A. All rights reserved. PIZSO921-5093(97)00151-2
transition during the process of deformation. For some time this obvious idea could not be realized because of technical problems. The advent of new deformation facilities [ll] has permitted the extension of the temperature range down to 0.4 K and has thus made the required experiments possible. Consideration of the observed regularities and their comparison with current hypotheses are presented in this study.
2. Initial experiments It appears likely that the problem of the influence of the superconducting transition on jump-like deformation was, for the first time, approached in the study on niobium single crystals [4]. At 2.17 K appreciable difference appeared between the stresses of the onset of jump-like deformation. In the normal state jumps occurred earlier (roN = 165 MPa) than in the superconducting state (zos = 208 MPa). The result at 4.2 k was less distinct. The fact that the experiment was performed on two samples reduces the reliability of the results. The experiment studying the N-S transition influence on the deforming stress of Pb and its alloys [12] revealed appreciable deviations in the character of deformation. The superconducting transition either led to the disappearance of jumps or considerably decreased
158
V. V. Pustovalov
/Materials
Science
and Engineering
their amplitude. Systematic investigations are required to clear up the general regularities of the influence produced by the superconducting transition.
3. Experimental technique Superconductors which exhibited jump-like deformation below 4.2 K were investigated, including pure metals (Al, Pb, In) and alloys (In-Pb, Al-Mg, Al-Mn, Al-Li) at several concentrations. Both single and polycrystals were subjected to tension and compression at a constant strain rate (10 - 4- 10- 5 s ~ ‘) in the temperature range 4.2-0.5 K using an original unit [ll] and a three-step cooling system with liquid nitrogen, helium-4 and helium-3.
4. Results 4.1. Pure metals The samples were aluminium (99.5%) [13] polycrystals in which LTJD is well developed. The S-N and N-S transitions were achieved by switching on and off the magnetic field of H N 150 mT. Jump-like deformation first appears only in the N-state. In the N-S transition, the jumps disappear. In the S-state jumps were observed immediately before the sample fracture. A qualitatively similar result was obtained on deforming identical samplesat the sametemperature, - 0.8 K, but the samples were in different states. Next, we wanted to find out to what extent this behaviour is typical. Pb (99.997%) polycrystals were deformed under tension and compression [14]. Macroscopic jumps appeared below 1 K. Jump-like deformation is typically observed in the N-state and is enhanced when the temperature decreases.Thorough studies were also performed on In single crystals [15]. The axis of compression runs halfway between the directions [loo] and [l lo]. The experiments with periodically alternating states show that the character of jump-like deformation is dependent on the degree of deformation and the state of the sample. The first jump appears in the N-state. Their frequency increaseswith deformation. Individual jumps are observed in the S-state too. Later on deformation is jump-like both in the N- and S-states but the jump amplitudes are about 2.5 times larger in the N-state.
A234-236
(1997)
157-160
jumps can be observed only in the N-state, with the transition of the sample to the S-state they completely disappear. As deformation increases, jumps start appearing in the S-state as well. Their amplitudes and frequency increase with deformation reaching, at a certain stage, the amplitudes and frequency of the N-state. In Al-Li alloys jump-like deformation occurs at 4.2 K and below. The following principal regularities of jump-like deformation have been found for quenched Al-Li alloys of three concentrations (3.8, 7.0 and 10.4 at.% Li). At higher impurity concentrations it develops in smaller degrees of deformation and the frequency and amplitudes of jumps increase. A similar effect is observed with decreasing temperature. At constant temperatures and Li concentrations the amplitudes and frequency of jumps increase gradually with deformation and the intervals between them decrease. The influence of the electronic state of the sampleson jump-like deformations is illustrated in Fig. 2. A change to the S-state either terminates jump-like deformation (at low deformation) or makes it appreciably weaker (moderate deformation). At a certain degree of deformation the N-S transition does not influence the character of plastic flow, just like in Al-Mg alloys.
Al-1,85%Mg i.i,f4d’C”
S
4.2. Alloys The results for alloys qualitatively agree with those for pure metals. Fig. 1 shows some portions of the stress-strain curves taken on Al-O.85 at.% Mg polycrystals under tension. At the beginning of deformation
Fig. 1. Portion of tensile stress-strain curve taken on the Al-l.85 at.O% Mg polycrystal with a change in the electronic state of the sample during deformation. T=0.5 K, e= 1.1.10V5 SC’ [16].
V. V. Pustovalov
/Materials
Science
and Engineering
E=0.0%
E - 3.4%
PP S
N
S N
s
s
m
RI
“s “! I 0-
!i “! I 0-
0.1%
0.1%
E = 29%
E-21% N
S
S P GJ
11 d - 0.1%
Q
f
41
1%
--
Fig. 2. Portions of the tensile stress-strain curve illustrating the influencing of the N-S transition upon jump-like deformation: Al-3.8 at.% Li, T=O.S K, Z:= lop5 ssi [17].
5. Discussion The studies of jump-like deformation in normal, superconducting states and in the process of N =+=S, S *N transitions show that in the superconducting state macroscopic jump-like deformation is as a rule less developed or absent. This effect of N-S transition may be considered typical. In terms of concepts which treat the low temperature jump-like deformation as a manifestation of thermomechanical instability, the stress of the jump-like deformation onset r, at constant temperature and deformation rate is generally dependent on three physical parameters-thermal conductivity coefficient K, heat capacity C, and surface heat transfer coefficient h [4-91. Of these, h is independent of the electronic state, C varies appreciable only near T,, being C, N C, in all other cases. This means that z, can change only with K. We have knowledge of K about some of them-Al, Pb, Sn, where KS < KN. According to the mechanism of thermomechanical instability, r, should decrease during the N-S transition, i.e. jumplike deformation is expected to be enhanced. Experiments show the reverse effect. To explain the
A234-236
(1997)
157-160
159
discrepancy observed, a modified theory was proposed which allowed for the temperature dependence of the flow stress [18,19]. Within this theoretical model, the N-S transition can influence jump-like deformation in different ways. The type of influence depends on the sign of dz/dT and its change in the process of the N-S transition. The data available about the temperature dependencies of zO, go, z,,,, g,,, [13- 181 show that different dependencies s(T) are observed, and the sign of dz/dT either does not change (dz/dT > 0, dz/dT < 0) or (dr/dT = 0) in a very narrow interval near T,. The influence of the N-S transition on jump-like deformation is the same irrespective of all 7(T) and dz/dT variations. It is a change in the dependence z(T) that can cause extinction of jump-like deformation in the superconducting state. Let us compare these regularities with the dynamic dislocation hypothesis [lo]. Proceeding from current concepts of dislocation motion in the normal and superconducting states [1,2], we can explain the influence of the N-S transition on jump-like deformation. Against the N-state, some obstacles in the S-state can be overcome due to the inertial effects. The jumps will appear later on and their amplitudes will be smaller under the same deformation. With any z(T), the process may be seen as single jumps or a serrated curve. Within this model the process of jump-like deformation does not require r to decrease with increasing temperature. The absence of any influence of the N-S transition upon jump-like deformation under high stresses in high-strength Al alloys is most likely due to weak heating (0.5-1.2 K) of the sample and its switching over to the normal state. The results from the influence of the superconducting transition upon jumplike deformation favor of the dynamic hypothesis.
References 111V.I.
Startsev, V.Y. Il’itchev and V.V. Pustovalov, Plasticity and Strength of Metals and Alloys at Low Temperatures, Metallurgia, Moscow, 1975, p. 325 (in Russian). (Ed.), Dislocation in Solids, PI V.I. Startsev, in: F.R.N. Nabarro Vol. 6, North Holland, Amsterdam, 1983, p. 145. Proc. R. Sot. London, Ser. A 240 (1957) 229. 131 Z.S. Basinski, B. Jouffrey, Phil. Mag. 24 (N188) (1971) 437. 141 L.P. Kubin, S. Takeuchi, T. Suzuki, J. Phys. Sot. Jpn. 34 (N5) 151E. Kuramoto, (1973) 1217. 161G.A. Malygin, Phys. Stat. Sol. (b) 61 (1974) K45. Yu.Z. Estrin, Sov. Phys. Solid State 17 (N7) [71 B.V. Petukhov, (1975) 1333. 181Yu.Z. Estrin, L.P. Kubin, Ser. Metall. 14 (N12) (1980) 1359. I.N. Nechiporenko, Sov. J. Low Temp. Phys. 4 [91 IS. Zhitomirski, (NS) (1978) 499. 1101A. Seeger, in: J.C. Fisher, W.G. Johnston, K. Thomson, T. Vreeland (Eds.), Dislocation and Mechanical Properties of Crystals, Wiley, New York, 1957. V.S. Fomenko, Y.I. Gofman, Preprint FTINT 1111V.V. Pustovalov, AN Ukr. SSR, 6 October 1972, Kharkov, p. 17 (in Russian).
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/Materials
Science
and Engineering
[12] T.A. Parkhomenko, IN. Kuzmenko, V.V. Pustovalov, Sov. Low Temp. Phys. 4 (NlO) (1978) 632. [13] I.N. Kuzmenko, V.V. Pustovalov, Sov. J. Low Temp. Phys. 5 (N12) (1979) 679. [14] I.N. Kuzmenko, V.V. Pustovalov, Sov. Phys. Doklady, 44 (1985) 50 (English translation). [15] I.N. Kuzmenko, S.V. Lubenets, V.V. Pustovalov, S.E. Shumilin,
A234-236
(1997)
157-160
Sov. J. Low Temp. Phys. 9 (N8) (1983) 450. [16] V.V. Pustovalov, S.E. Shumilin, Sov. Phys. Phys. Metal. Metallogr. 52 (Nl) (1986) 57. [17] N.V. Isaev, V.V. Pustovalov, V.S. Forenko, S.E. Shumilin, Low Temp. Phys. 20 (N8) (1994) 653. [18] G.A. Malygin, Sov. J. Low Temp. Phys. 12 (N8) (1986) 481. [19] I.N. Nechiporenko, Sov. J. Low Temp. Phys. 12 (Nl) (1986) 43.