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Electrical resistance behaviour of Fe–24 wt.%Mn alloy under high pressure
Materials Research Bulletin 37 (2002) 1233±1238
Electrical resistance behaviour of Fe±24 wt.%Mn alloy under high pressure M. Sekar*, P.Ch. Sahu, N.V. Chandra Shekar, Mohammad Yousuf, K. Govinda Rajan Materials Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamil Nadu, India (Refereed) Received 29 June 2001; accepted 15 April 2002
Abstract Electrical resistance behaviour of Fe±24 wt.%Mn SMA was studied up to a pressure of 6 GPa by using an opposed anvil high pressure device. The system shows a steep rise in resistance up to 1 GPa and thereafter a monotonic decrease up to 6 GPa during the forward cycle, whereas it shows a monotonic increase during the return cycle. XRD studies of the asprepared and pressure quenched samples show a mixed a, g and e phase in the former and a predominantly e phase in the latter, indicative of a possible structural transition at 1 GPa, as evidenced from the resistance maximum. The decrease in the transition pressure, when compared with alloys of lower Mn concentration, provides a clue that it should be possible to further reduce the transition pressure to the predominantly e phase by alloying with suitable elements, which may have positive effect on the shape memory of the alloy. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: A. Alloys; A. Intermetallic compounds; C. High pressure; D. Electrical properties; C. Xray diffraction
1. Introduction Typical shape memory alloys (SMAs) based on nickel, copper and iron have great technological importance [1,2]. The shape memory effect (SME) in several of these alloys has been studied as a function of temperature and uniaxial stress to learn about *
Corresponding author. Tel.: 91-4114-480-347; fax: 91-4114-480-081. E-mail address: [email protected] (M. Sekar).
0025-5408/02/$ ± see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 2 5 - 5 4 0 8 ( 0 2 ) 0 0 7 6 9 - 9
1234
M. Sekar et al. / Materials Research Bulletin 37 (2002) 1233±1238
their martensitic transformation behaviour [2]. However, high pressure work on these SMAs is very sparse. The role of high pressures in in¯uencing phase transitions and in unravelling transition mechanisms is well known [3±5]. The Fe±Mn and Fe±Mn±Si SMA systems were ®rst introduced by Japanese workers and these alloys were considered having potential applications in space technology by offering alternate options for couplings and fasteners [2]. The SME in the Fe±Mn systems is ascribed to the g±e martensite transformation [6,7]. In this paper, the pressure induced martensitic transformation behaviour of the Fe±24 wt.%Mn alloy is reported up to a pressure of 6 GPa at 300 K using electrical resistance measurement as well as X-ray diffraction (XRD) techniques. 2. Experimental The Fe±24 wt.%Mn SMA was prepared by induction melting of the constituent elements in an inert environment and was homogenized at 12508C for 24 h by vacuum sealing the melted sample in a quartz ampule. It was next hot rolled into a thin plate of thickness 1.5 mm and then sliced into thin strips of size 3 mm 1 mm 0:2 mm using a diamond saw. The cut specimens were again vacuum sealed in quartz tube, annealed at 10008C for 10 min and then water quenched. The composition of the sample was con®rmed by atomic absorption photospectrometry. In order to ®nd out the austenite to martensite transformation temperatures of the alloy, differential scanning calorimetry was carried out. The observed transformation temperatures were found to be in agreement with the reported values [8]. High pressure electrical resistance measurement on these samples were carried out up to a pressure of 6 GPa in an opposed anvil high pressure device using pyrophyllite as the gasket, steatite as the pressure transmitting medium and bismuth as the internal pressure calibrant. The details of the four probe high pressure electrical resistance measurement technique are given in [9]. XRD of the as-prepared sample as well as the pressure treated samples were carried out using a high precision Guinier diffractometer coupled to a Rigaku 18 kW rotating anode X-ray generator. A scintillation detector was used for detecting the diffracted beam. It is known that a Guinier diffractometer provides high-resolution XRD data with better S/N ratio. The use of curved crystal monochromator provides pure Mo Ka1 radiation and the focusing action increases the X-ray photon ¯ux, thereby decreasing the data-acquisition time substantially. The overall resolution of this set up is Dd/d 0:005 [10]. 3. Results and discussion The variation of the normalized resistance (Rp/R1 bar) of Fe±24 wt.%Mn as a function of pressure is depicted in Fig. 1. Initially, there is a steep rise in resistance up to a pressure of 1 GPa followed by a monotonic decrease up to 6 GPa. The change in resistance behaviour at 1 GPa could be attributed to a phase transformation in this
M. Sekar et al. / Materials Research Bulletin 37 (2002) 1233±1238
1235
Fig. 1. The normalized resistance (Rp/R1 bar) of Fe±24 wt.%Mn as a function of pressure up to 6 GPa. A change in the resistance behaviour with pressure around 1 GPa during the forward cycle can be noticed. This is indicative of a phase transition at 1 GPa. The return cycle shows continuous increase in resistance with decrease of pressure, indicating the irreversible nature of the above transition.
alloy. It can be noted from the ®gure that the initial increase in resistance is 4.5% in the pressure range 0.1 MPa to 1 GPa followed by a monotonic fall of 2% in the range 1±6 GPa. During the return cycle, the resistance retraces the path from 6 to 1 GPa, but shows a continuous increase below 1 GPa, indicating the irreversible nature of the above transition. This result is similar to the earlier work on Fe± 24 wt.%Mn±6 wt.%Si, but for a small cusp at 0.5 GPa observed in the latter [11]. In order to understand the pressure induced resistance behaviour of this SMA in a better way, XRD measurements were carried out on the as-prepared as well as the pressure quenched samples. Fig. 2(a) shows the XRD pattern of the as-prepared sample and Fig. 2(b) shows that of the pressure quenched sample at 6 GPa. All the peaks were indexed by comparing the available XRD data on the Fe±Mn phases [12,13] as well as that of the a-Fe and e-Fe phases. The XRD pattern of the asprepared sample (Fig. 2(a)) shows a mixed a, g and e phase (the g phase being predominant), whereas the pattern corresponding to the pressure quenched sample (Fig. 2(b)) shows mostly the e phase. The presence of a phase in addition to g and e phases may be attibuted to the formation of demangenisation at least on the surface of the as-prepared sample [14]. The XRD patterns reported in this paper have more number of better resolved Bragg peaks as compared to the patterns reported by [12].
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M. Sekar et al. / Materials Research Bulletin 37 (2002) 1233±1238
Fig. 2. X-ray diffraction pattern of Fe±24 wt.%Mn sample: (a) as-prepared: indicating the existence of the a, g and e phases and (b) pressure quenched at 6 GPa: showing that the system is mostly in the e phase. The peaks are identi®ed in Table 1.
Table 1 summarises the XRD results obtained in this investigation. It can be seen from the table that the as-prepared sample is a mixture of the a, g and e phases, where as the pressure quenched sample is mostly in the e phase. This implies that the system might have undergone an irreversible transition from a, g to a predominantly e phase under pressure. The upward arrow in the table indicates an increase in the intensity of the diffraction peaks and the downward arrow a decrease. The decrease in the intensities of the g(1 1 1), a(1 1 0), g(2 0 0), a(2 0 0), g(2 2 0) and g(3 1 1) peaks in the pressure quenched sample can be seen from the table. This shows that the concentration of Table 1 Summary of the X-ray diffraction results on the as-prepared and pressure quenched (at 6 GPa) Fe± 24 wt.%Mn sample Peak no.
1 2 3 4 5 6 7 8 9 10 11
As-prepared Fe±24 wt.%Mn
Pressure quenched Fe±24 wt.%Mn
hkl
Ê) d (A
I/I0 (%)
hkl
Ê) d (A
I/I0 (%)
e (1 0 0) g (1 1 1) e (0 0 2) a (1 1 0) e (1 0 1) g (2 0 0) a (2 0 0) e (1 0 2) e (1 1 0) g (2 2 0) a (2 1 1) e (1 1 1) e (1 1 2) g (3 1 1) e (2 0 0) e (2 0 1)
2.202 2.083 2.050 1.940 1.806 1.501 1.272 1.161 1.088 1.065 1.040
20 100 11 85 42 12 57 6 28 6 2
e (1 0 0) g (1 1 1) e (0 0 2) a (1 1 0) e (1 0 1) g (2 0 0) a (2 0 0) e (1 0 2) e (1 1 0) g (2 2 0) a (2 1 1) e (1 1 1) e (1 1 2) g (3 1 1) e (2 0 0) e (2 0 1)
2.202 2.079 2.052 1.939 1.802 1.496 1.271 1.158 1.082 1.060 ±
40" 21# 3# 100" 5# 5# 18# 4# 8# 5 ±
Increase in the e concentration in the pressure quenched sample is evident.
M. Sekar et al. / Materials Research Bulletin 37 (2002) 1233±1238
1237
E phase enhances and gets stabilized under high pressure at the cost of the a and g phases during the above irreversible transition. The irreversibility of this transition is consistent with the observed resistance behaviour under high pressure. The initial increase in resistance up to 1 GPa is probably due to stabilization of the e phase endowed with higher resistivity at the cost of a and g phases associated with lower resistivity. In fact, in pure Fe, it has been seen that there is a drastic increase in resitance by 260% when it transforms from the a to the e phase [15]. Hence, similar resistance behaviour in Fe±24 wt.%Mn across a, g to the predominantly e phase at 1 GPa is not surprising. The decrease in resistance in the pressure range 1±6 GPa is probably due to the compression of the e phase, as the resistance of a metal generally decreases with pressure. During the return cycle, the resistance behaviour retracing the path from 6 to 1 GPa and continuing the increasing trend below 1 GPa is indicative of the irreversibility of the above transition. Pressurising the sample again should show the usual resistance behaviour of a typical metal, i.e. continuous decrease with pressure. In fact, this expected behaviour was observed in all the subsequent pressure runs. All the above observed features strongly establish an irreversible phase transition from a, g to a predominantly e phase at 1 GPa. The irreversibility of the g±e transition is also seen by Mossbauer-XRD experiments of Trichter et al. [16]. It has been reported that at room temperature, a-Fe (bcc phase) transforms to e-Fe (hcp phase) at 12.5 GPa [13], and that the transition pressure decreases with increase in the Mn content. For example, the mixed a, g ! e transition occurs at 5.5 GPa for Fe±11 wt.%Mn [17] and 3.5 GPa for Fe±14 wt.%Mn [12]. In our work, the Mn content is 24 wt.% and it is observed that the transition pressure is lowered to 1 GPa (Fig. 1). It is known that lowering of the transition pressure to the e phase enhances the SME. Hence alloying with suitable elements can further bring down the transition pressure to the e phase, thereby enhancing the SME. In fact, it has been seen that in Fe±24 wt.%Mn±6 wt.%Si, the transformation pressure to the e phase has decreased to 0.8 GPa [11] with considerable enhancement of SME by alloying with Si. Further enhancement of SME can be achieved by alloying with other suitable elements. Acknowledgments The authors thank Dr. H.P. Nawada and Dr. T.R. Mahalingam for their help in performing DSC and atomic absorption photo spectrometry experiments, respectively on Fe±24 wt.%Mn alloy. The authors thank Shri L.M. Sundaram for his help at various stages of experiments.The authors also thank Dr. T.S. Radhakrishnan and Dr. Baldev Raj for their constant encouragement and support. References [1] L. Delaey, in: R.W. Cahn, P. Haasen, E.J. Kramer (Eds.), Materials Science and Technology, Vol. 5, VCH, Weinheim, 1991, p. 339.
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M. Sekar et al. / Materials Research Bulletin 37 (2002) 1233±1238
[2] L.M. Schetky, Engineering Aspects of Shape Memory Alloys, in: T.W. Duerig, K.N. Melton, D. Stockel, C.M. Wayman (Eds.), Butterworth, London, 1990, p. 170. [3] J.S. Schilling, J. Phys. Chem. Solids. 59 (1998) 553. [4] P.Ch. Sahu, K. Govinda Rajan, N.V. Chandra Shekar, M. Yousuf, in: V. Kumar, S. Sengupta, B. Raj (Eds.), Frontiers in Materials Modelling and Design, Springer Verlag, Heidelberg, 1997, p. 365. [5] N.V. Chandra Shekar, K. Govinda Rajan, Bull. Mater. Sci. 24 (2001) 1. [6] M. Murakami, H. Otsuka, in: M. Doyama, S. Somiya, R.P.H. Chang (Eds.), Proceedings of the MRS International Meeting on Advanced Materials, Vol. 9, Shape Memory Materials, Materials Research Society, Pittsburg, 1989, p. 447. [7] H. Otsuka, M. Murakami, S. Matsuda, in: M. Doyama, S. Somiya, R.P.H. Chang (Eds.), Proceedings of the MRS International Meeting on Advanced Materials, Vol. 9, Shape Memory Materials, Materials Research Society, Pittsburg, 1989, p. 451. [8] Y. Tomota, W. Nakagawara, K. Tsuzaki, K. Maki, Scripta Metall. et Materialia 26 (1992) 1571. [9] M. Yousuf, P.Ch. Sahu, K. Govinda Rajan, Pramana 24 (1985) 825. [10] P.Ch. Sahu, M. Yousuf, N.V. Chandra Shekar, N. Subramanian, K. Govinda Rajan, Rev. Sci. Instrum. 66 (1995) 2599. [11] V. Saravanan, M. Sekar, K. Govinda Rajan, P.Ch. Sahu, M. Yousuf, N.V. Chandra Shekar, V. Victor Jaya, H. Ohtsuka, in: Proceedings of the International Conference on High Pressure Science and Technology, Joint AIRAPT-16 & HPCJ-38, Kyoto, 1997, p. 651. [12] P.M. Giles, A.R. Marder, Metall. Trans. 2 (1971) 1371. [13] T. Takahashi, W.A. Bassett, Science 145 (1964) 483. [14] B.H. Jiang, L. Sun, R. Li, T.Y. Hsu, Scripta Metall. et Materialia 33 (1995) 63; B.H. Jiang, X. Qi, W. Zhou, T.Y. Hsu, Scripta Metall. et Materialia 34 (1996) 771. [15] A.S. Balchen, H.G. Drickamer, Rev. Sci. Instrum. 32 (1961) 308. [16] F. Trichter, A. Rabinkin, M. Ron, A. Sharfstein, Scripta Metall. et Materialia 12 (1978) 431. [17] T.R. Loree, R.H. Warnes, E.G. Zukas, C.M. Fowler, Science 153 (1966) 1277.
Electrical resistance behaviour of Fe±24 wt.%Mn alloy under high pressure M. Sekar*, P.Ch. Sahu, N.V. Chandra Shekar, Mohammad Yousuf, K. Govinda Rajan Materials Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamil Nadu, India (Refereed) Received 29 June 2001; accepted 15 April 2002
Abstract Electrical resistance behaviour of Fe±24 wt.%Mn SMA was studied up to a pressure of 6 GPa by using an opposed anvil high pressure device. The system shows a steep rise in resistance up to 1 GPa and thereafter a monotonic decrease up to 6 GPa during the forward cycle, whereas it shows a monotonic increase during the return cycle. XRD studies of the asprepared and pressure quenched samples show a mixed a, g and e phase in the former and a predominantly e phase in the latter, indicative of a possible structural transition at 1 GPa, as evidenced from the resistance maximum. The decrease in the transition pressure, when compared with alloys of lower Mn concentration, provides a clue that it should be possible to further reduce the transition pressure to the predominantly e phase by alloying with suitable elements, which may have positive effect on the shape memory of the alloy. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: A. Alloys; A. Intermetallic compounds; C. High pressure; D. Electrical properties; C. Xray diffraction
1. Introduction Typical shape memory alloys (SMAs) based on nickel, copper and iron have great technological importance [1,2]. The shape memory effect (SME) in several of these alloys has been studied as a function of temperature and uniaxial stress to learn about *
Corresponding author. Tel.: 91-4114-480-347; fax: 91-4114-480-081. E-mail address: [email protected] (M. Sekar).
0025-5408/02/$ ± see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 2 5 - 5 4 0 8 ( 0 2 ) 0 0 7 6 9 - 9
1234
M. Sekar et al. / Materials Research Bulletin 37 (2002) 1233±1238
their martensitic transformation behaviour [2]. However, high pressure work on these SMAs is very sparse. The role of high pressures in in¯uencing phase transitions and in unravelling transition mechanisms is well known [3±5]. The Fe±Mn and Fe±Mn±Si SMA systems were ®rst introduced by Japanese workers and these alloys were considered having potential applications in space technology by offering alternate options for couplings and fasteners [2]. The SME in the Fe±Mn systems is ascribed to the g±e martensite transformation [6,7]. In this paper, the pressure induced martensitic transformation behaviour of the Fe±24 wt.%Mn alloy is reported up to a pressure of 6 GPa at 300 K using electrical resistance measurement as well as X-ray diffraction (XRD) techniques. 2. Experimental The Fe±24 wt.%Mn SMA was prepared by induction melting of the constituent elements in an inert environment and was homogenized at 12508C for 24 h by vacuum sealing the melted sample in a quartz ampule. It was next hot rolled into a thin plate of thickness 1.5 mm and then sliced into thin strips of size 3 mm 1 mm 0:2 mm using a diamond saw. The cut specimens were again vacuum sealed in quartz tube, annealed at 10008C for 10 min and then water quenched. The composition of the sample was con®rmed by atomic absorption photospectrometry. In order to ®nd out the austenite to martensite transformation temperatures of the alloy, differential scanning calorimetry was carried out. The observed transformation temperatures were found to be in agreement with the reported values [8]. High pressure electrical resistance measurement on these samples were carried out up to a pressure of 6 GPa in an opposed anvil high pressure device using pyrophyllite as the gasket, steatite as the pressure transmitting medium and bismuth as the internal pressure calibrant. The details of the four probe high pressure electrical resistance measurement technique are given in [9]. XRD of the as-prepared sample as well as the pressure treated samples were carried out using a high precision Guinier diffractometer coupled to a Rigaku 18 kW rotating anode X-ray generator. A scintillation detector was used for detecting the diffracted beam. It is known that a Guinier diffractometer provides high-resolution XRD data with better S/N ratio. The use of curved crystal monochromator provides pure Mo Ka1 radiation and the focusing action increases the X-ray photon ¯ux, thereby decreasing the data-acquisition time substantially. The overall resolution of this set up is Dd/d 0:005 [10]. 3. Results and discussion The variation of the normalized resistance (Rp/R1 bar) of Fe±24 wt.%Mn as a function of pressure is depicted in Fig. 1. Initially, there is a steep rise in resistance up to a pressure of 1 GPa followed by a monotonic decrease up to 6 GPa. The change in resistance behaviour at 1 GPa could be attributed to a phase transformation in this
M. Sekar et al. / Materials Research Bulletin 37 (2002) 1233±1238
1235
Fig. 1. The normalized resistance (Rp/R1 bar) of Fe±24 wt.%Mn as a function of pressure up to 6 GPa. A change in the resistance behaviour with pressure around 1 GPa during the forward cycle can be noticed. This is indicative of a phase transition at 1 GPa. The return cycle shows continuous increase in resistance with decrease of pressure, indicating the irreversible nature of the above transition.
alloy. It can be noted from the ®gure that the initial increase in resistance is 4.5% in the pressure range 0.1 MPa to 1 GPa followed by a monotonic fall of 2% in the range 1±6 GPa. During the return cycle, the resistance retraces the path from 6 to 1 GPa, but shows a continuous increase below 1 GPa, indicating the irreversible nature of the above transition. This result is similar to the earlier work on Fe± 24 wt.%Mn±6 wt.%Si, but for a small cusp at 0.5 GPa observed in the latter [11]. In order to understand the pressure induced resistance behaviour of this SMA in a better way, XRD measurements were carried out on the as-prepared as well as the pressure quenched samples. Fig. 2(a) shows the XRD pattern of the as-prepared sample and Fig. 2(b) shows that of the pressure quenched sample at 6 GPa. All the peaks were indexed by comparing the available XRD data on the Fe±Mn phases [12,13] as well as that of the a-Fe and e-Fe phases. The XRD pattern of the asprepared sample (Fig. 2(a)) shows a mixed a, g and e phase (the g phase being predominant), whereas the pattern corresponding to the pressure quenched sample (Fig. 2(b)) shows mostly the e phase. The presence of a phase in addition to g and e phases may be attibuted to the formation of demangenisation at least on the surface of the as-prepared sample [14]. The XRD patterns reported in this paper have more number of better resolved Bragg peaks as compared to the patterns reported by [12].
1236
M. Sekar et al. / Materials Research Bulletin 37 (2002) 1233±1238
Fig. 2. X-ray diffraction pattern of Fe±24 wt.%Mn sample: (a) as-prepared: indicating the existence of the a, g and e phases and (b) pressure quenched at 6 GPa: showing that the system is mostly in the e phase. The peaks are identi®ed in Table 1.
Table 1 summarises the XRD results obtained in this investigation. It can be seen from the table that the as-prepared sample is a mixture of the a, g and e phases, where as the pressure quenched sample is mostly in the e phase. This implies that the system might have undergone an irreversible transition from a, g to a predominantly e phase under pressure. The upward arrow in the table indicates an increase in the intensity of the diffraction peaks and the downward arrow a decrease. The decrease in the intensities of the g(1 1 1), a(1 1 0), g(2 0 0), a(2 0 0), g(2 2 0) and g(3 1 1) peaks in the pressure quenched sample can be seen from the table. This shows that the concentration of Table 1 Summary of the X-ray diffraction results on the as-prepared and pressure quenched (at 6 GPa) Fe± 24 wt.%Mn sample Peak no.
1 2 3 4 5 6 7 8 9 10 11
As-prepared Fe±24 wt.%Mn
Pressure quenched Fe±24 wt.%Mn
hkl
Ê) d (A
I/I0 (%)
hkl
Ê) d (A
I/I0 (%)
e (1 0 0) g (1 1 1) e (0 0 2) a (1 1 0) e (1 0 1) g (2 0 0) a (2 0 0) e (1 0 2) e (1 1 0) g (2 2 0) a (2 1 1) e (1 1 1) e (1 1 2) g (3 1 1) e (2 0 0) e (2 0 1)
2.202 2.083 2.050 1.940 1.806 1.501 1.272 1.161 1.088 1.065 1.040
20 100 11 85 42 12 57 6 28 6 2
e (1 0 0) g (1 1 1) e (0 0 2) a (1 1 0) e (1 0 1) g (2 0 0) a (2 0 0) e (1 0 2) e (1 1 0) g (2 2 0) a (2 1 1) e (1 1 1) e (1 1 2) g (3 1 1) e (2 0 0) e (2 0 1)
2.202 2.079 2.052 1.939 1.802 1.496 1.271 1.158 1.082 1.060 ±
40" 21# 3# 100" 5# 5# 18# 4# 8# 5 ±
Increase in the e concentration in the pressure quenched sample is evident.
M. Sekar et al. / Materials Research Bulletin 37 (2002) 1233±1238
1237
E phase enhances and gets stabilized under high pressure at the cost of the a and g phases during the above irreversible transition. The irreversibility of this transition is consistent with the observed resistance behaviour under high pressure. The initial increase in resistance up to 1 GPa is probably due to stabilization of the e phase endowed with higher resistivity at the cost of a and g phases associated with lower resistivity. In fact, in pure Fe, it has been seen that there is a drastic increase in resitance by 260% when it transforms from the a to the e phase [15]. Hence, similar resistance behaviour in Fe±24 wt.%Mn across a, g to the predominantly e phase at 1 GPa is not surprising. The decrease in resistance in the pressure range 1±6 GPa is probably due to the compression of the e phase, as the resistance of a metal generally decreases with pressure. During the return cycle, the resistance behaviour retracing the path from 6 to 1 GPa and continuing the increasing trend below 1 GPa is indicative of the irreversibility of the above transition. Pressurising the sample again should show the usual resistance behaviour of a typical metal, i.e. continuous decrease with pressure. In fact, this expected behaviour was observed in all the subsequent pressure runs. All the above observed features strongly establish an irreversible phase transition from a, g to a predominantly e phase at 1 GPa. The irreversibility of the g±e transition is also seen by Mossbauer-XRD experiments of Trichter et al. [16]. It has been reported that at room temperature, a-Fe (bcc phase) transforms to e-Fe (hcp phase) at 12.5 GPa [13], and that the transition pressure decreases with increase in the Mn content. For example, the mixed a, g ! e transition occurs at 5.5 GPa for Fe±11 wt.%Mn [17] and 3.5 GPa for Fe±14 wt.%Mn [12]. In our work, the Mn content is 24 wt.% and it is observed that the transition pressure is lowered to 1 GPa (Fig. 1). It is known that lowering of the transition pressure to the e phase enhances the SME. Hence alloying with suitable elements can further bring down the transition pressure to the e phase, thereby enhancing the SME. In fact, it has been seen that in Fe±24 wt.%Mn±6 wt.%Si, the transformation pressure to the e phase has decreased to 0.8 GPa [11] with considerable enhancement of SME by alloying with Si. Further enhancement of SME can be achieved by alloying with other suitable elements. Acknowledgments The authors thank Dr. H.P. Nawada and Dr. T.R. Mahalingam for their help in performing DSC and atomic absorption photo spectrometry experiments, respectively on Fe±24 wt.%Mn alloy. The authors thank Shri L.M. Sundaram for his help at various stages of experiments.The authors also thank Dr. T.S. Radhakrishnan and Dr. Baldev Raj for their constant encouragement and support. References [1] L. Delaey, in: R.W. Cahn, P. Haasen, E.J. Kramer (Eds.), Materials Science and Technology, Vol. 5, VCH, Weinheim, 1991, p. 339.
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[2] L.M. Schetky, Engineering Aspects of Shape Memory Alloys, in: T.W. Duerig, K.N. Melton, D. Stockel, C.M. Wayman (Eds.), Butterworth, London, 1990, p. 170. [3] J.S. Schilling, J. Phys. Chem. Solids. 59 (1998) 553. [4] P.Ch. Sahu, K. Govinda Rajan, N.V. Chandra Shekar, M. Yousuf, in: V. Kumar, S. Sengupta, B. Raj (Eds.), Frontiers in Materials Modelling and Design, Springer Verlag, Heidelberg, 1997, p. 365. [5] N.V. Chandra Shekar, K. Govinda Rajan, Bull. Mater. Sci. 24 (2001) 1. [6] M. Murakami, H. Otsuka, in: M. Doyama, S. Somiya, R.P.H. Chang (Eds.), Proceedings of the MRS International Meeting on Advanced Materials, Vol. 9, Shape Memory Materials, Materials Research Society, Pittsburg, 1989, p. 447. [7] H. Otsuka, M. Murakami, S. Matsuda, in: M. Doyama, S. Somiya, R.P.H. Chang (Eds.), Proceedings of the MRS International Meeting on Advanced Materials, Vol. 9, Shape Memory Materials, Materials Research Society, Pittsburg, 1989, p. 451. [8] Y. Tomota, W. Nakagawara, K. Tsuzaki, K. Maki, Scripta Metall. et Materialia 26 (1992) 1571. [9] M. Yousuf, P.Ch. Sahu, K. Govinda Rajan, Pramana 24 (1985) 825. [10] P.Ch. Sahu, M. Yousuf, N.V. Chandra Shekar, N. Subramanian, K. Govinda Rajan, Rev. Sci. Instrum. 66 (1995) 2599. [11] V. Saravanan, M. Sekar, K. Govinda Rajan, P.Ch. Sahu, M. Yousuf, N.V. Chandra Shekar, V. Victor Jaya, H. Ohtsuka, in: Proceedings of the International Conference on High Pressure Science and Technology, Joint AIRAPT-16 & HPCJ-38, Kyoto, 1997, p. 651. [12] P.M. Giles, A.R. Marder, Metall. Trans. 2 (1971) 1371. [13] T. Takahashi, W.A. Bassett, Science 145 (1964) 483. [14] B.H. Jiang, L. Sun, R. Li, T.Y. Hsu, Scripta Metall. et Materialia 33 (1995) 63; B.H. Jiang, X. Qi, W. Zhou, T.Y. Hsu, Scripta Metall. et Materialia 34 (1996) 771. [15] A.S. Balchen, H.G. Drickamer, Rev. Sci. Instrum. 32 (1961) 308. [16] F. Trichter, A. Rabinkin, M. Ron, A. Sharfstein, Scripta Metall. et Materialia 12 (1978) 431. [17] T.R. Loree, R.H. Warnes, E.G. Zukas, C.M. Fowler, Science 153 (1966) 1277.