- Email: [email protected]
Isothermal nature of the B2–B19′ martensitic transformation in a Ti–51.2Ni (at.%) alloy
Available online at www.sciencedirect.com
Scripta Materialia 68 (2013) 984–987 www.elsevier.com/locate/scriptamat
Isothermal nature of the B2–B190 martensitic transformation in a Ti–51.2Ni (at.%) alloy Takashi Fukuda,⇑ Shinji Yoshida and Tomoyuki Kakeshita Department of Materials Science and Engineering, Graduate School of Engineering, Osaka University, 2-1, Yamada-oka, Suita, Osaka 565-0871, Japan Received 5 February 2013; revised 25 February 2013; accepted 26 February 2013 Available online 14 March 2013
The B2–B190 transformation in Ti–51.2Ni (at.%) alloy exhibits a clear time dependence. The transformation starts after an incubation time when the specimen is held above Ms, and proceeds while holding in the temperature range between 160 and 100 K. The nose temperature is expected to be near 130 K. The reverse transformation also shows a clear time dependence. Ó 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Thermal activation; Titanium–nickel alloy; Shape memory alloy; Nucleation
Martensitic transformations (MTs) are frequently classified into two groups, i.e. athermal or isothermal MTs, from the viewpoint of kinetics [1,2]. In an athermal transformation, the volume fraction of the martensite is considered to depend on temperature but not on time. In an isothermal transformation, the volume fraction of the martensite phase depends on both temperature and time. However, we consider that MTs are intrinsically isothermal, and an athermal transformation is a special case of an isothermal transformation as pointed out by Kurdiumov [3]. This interpretation has been supported by several experimental results. For an example, an iron-based alloy exhibiting a clear C-curve in its time– temperature–transformation (TTT) diagram transforms instantaneously when a magnetic field is applied [4]. In addition, an iron-based alloy which has a clear Ms temperature exhibits a C-curve in its TTT diagram when a hydrostatic pressure is applied [4]. These results imply that athermal and isothermal transformations are intrinsically the same in nature. Considering the isothermal nature of MTs, it is expected that a MT should occur even above the Ms (martensite start temperature) after some incubation time when the specimen is held below the equilibrium temperature T0. This prediction was confirmed to be correct in a Fe–Ni alloy [4], in a Cu–Al–Ni alloy [5] and in
⇑ Corresponding
author. Tel.: +81 6 6879 7483; fax: +81 6 6879 7522.; e-mail: [email protected]
Ni–Co–Mn–In alloy [6]. Moreover, the time dependence of MTs was recently found in many shape memory alloys [7–13]. However, there is an opposing interpretation of the kinetics of martensitic transformation. Otsuka et al. [14] examined the time dependence of the B2–B190 transformation by using a Ti–50Ni (at.%) alloy. They held the specimen for 21 days at a temperature above its Ms, and reported that no change in resistivity was detected. From their result, they concluded that the B2– B190 transformation in Ti–Ni alloy does not depend on time. They considered that the time dependence reported in the Cu–Al–Ni is due to diffusion of atoms while holding near 200 K. Recently, the kinetics of the B2–B190 transformation was re-examined by Kustov et al. [15] for a Ti– 50.2Ni (at.%) alloy. They held the specimen at a temperature in between its Ms and Mf, and reported that the transformation proceeds isothermally while holding at that temperature. However, they were not able to detect a clear incubation time before the martensitic transformation. In addition, they were not able to detect any time dependence for the reverse transformation. Based on this observation, they considered that although the growth process of the B2–B190 transformation depends on time, the nucleation process does not depend on time. We consider that the kinetics of the B2–B190 transformation is the same as that of other MTs. Therefore, an incubation time should exist for the transformation even though detection of this may not be easy. The aim of the
1359-6462/$ - see front matter Ó 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.scriptamat.2013.02.057
T. Fukuda et al. / Scripta Materialia 68 (2013) 984–987
present study is to show the existence of an incubation time for the B2–B190 transformation. We considered that selection of the alloy is crucial to detecting the incubation time for the B2–B190 transformation, i.e. the incubation time will be detected clearly by using an alloy with a low Ms temperature. A clear time dependence of MT was reported in an alloy with low Ms in a Ni45Co5Mn36.5In13.5 alloy [6]. According to previous studies, the Ms temperature of the B2–B190 transformation in binary Ti–Ni alloys decreases nearly linearly with increasing Ni content, and disappears suddenly near a Ni content of 51.5 at.% [16]. By making some preliminary experiments, we selected Ti–51.2Ni (at.%) alloy to investigate the time dependence of the B2–B190 transformation. An ingot of Ti–51.2Ni (at.%) alloy of nominal composition was prepared by an arc melting method. It was remelted several times to ensure homogeneity. The ingot was heat-treated at 1273 K for 24 h in vacuo and quenched into ice water. A specimen for electrical resistivity measurement (10 mm 2 mm 0.3 mm) and a specimen for differential scanning calorimetry (DSC, 3 mm 3 mm 1 mm) were cut from the ingot, and heat-treated at 1273 K in vacuo for 1 h followed by quenching into ice water. The surface of each specimen was electropolished in an electrolyte composed of acetic acid and perchloric acid. The electrical resistivity was measured by a four-probe method with a current of 200 mA and a frequency of 10 Hz. The specimen for the resistivity measurement was mounted on a copper stage using silicone grease, and the temperature of the stage was monitored throughout the measurements. The overshoot and undershoot of the temperature before isothermal holding was within 100 mK, and the fluctuation of the temperature while holding was within 10 mK. The DSC measurement was made in the temperature range between 353 and 123 K with a cooling and heating rate of 5 K min1. The DSC curve of the Ti–51.2Ni alloy exhibited an exothermic peak starting at 156 K in the cooling process and an endothermic peak ending at 215 K in the heating process. The latent heat obtained from the heating curve was 5.2 J g1 (0.28 kJ mol1), and the entropy change was estimated to be about 0.025 J g1 K1. This value is approximately one-half of that of Ti–50.9Ni alloy (0.050 J g1 K1) [17]. This difference suggests that nearly one-half of the specimen does not transform at a cooling rate of 5 K min1. Presumably, the progress of the martensitic transformation is suppressed by the internal stress. The isothermal nature of the B2–B190 transformation has been examined in detail by electrical resistivity measurements. We performed several thermal cycles for the investigation. Since the B2–B190 transformation temperature is known to depend on thermal cycling, the number of thermal cycles after the heat treatment is noted below. Figure 1 shows electrical resistivity curves measured with a cooling and heating rate of 2 K min1. During the cooling process of the first cycle, the resistivity starts to decrease at 154 K. The decrease in resistivity is due to the B2–B190 transformation. During the heating process, the resistivity curves start to deviate from that of
985
Figure 1. Temperature dependence of the electrical resistivity of a Ti– 51.2Ni alloy. The resistivities of the first and third cycles are shifted by +40 and 40 lX cm. Isothermal holding was done at 160, 155, 150, 145, 130, 115, 100 and 85 K in the cooling process of the second cycle and at 100, 115, 130, 145, 180, 185, 195 and 205 K in the heating process of the third cycle.
the cooling curve at 98 K, and then start to decrease with increasing temperature. The decrease in resistivity above 98 K strongly suggests that the B2–B190 transformation proceeds even during the heating process. Then, on further heating, the resistivity starts to increase at 187 K, which is due to the reverse transformation. In the second cycle, we made a step cooling experiment followed by a continuous heating, as reported by Planes et al. [7]. The specimen was cooled to a set temperature at a rate of 2 K min1, and then held at the temperature for 3 ks, followed by cooling to the next set temperature at a rate of 2 K min1. The set temperatures were 160, 155, 150, 145, 130, 115, 100 and 85 K. The vertical line of the resistivity curve in the second cycle is due to the progress of martensitic transformation while holding. Figure 2a–c shows the time dependence of the resistivity of the specimen at representative holding temperatures in the second cycle. When the specimen is held at 160 K (Fig. 2a), which is 6 K higher than the peak temperature of resistivity in the first cycle, the resistivity starts to decrease after a holding time of about 2.5 ks as indicated by an arrow. This result indicates that the B2–B190 transformation initiates after an incubation time of 2.5 ks. The holding temperature of 160 K is expected to be above the Ms of this cycle although we are not sure of the precise Ms temperature of the second cycle. When the specimen is held at 155 K (Fig. 2b), the resistivity starts to decrease as soon as the holding starts, meaning that the transformation occurs without detectable incubation time while holding at 155 K. A similar time dependence of resistivity was observed at 150,
986
T. Fukuda et al. / Scripta Materialia 68 (2013) 984–987
Figure 3. Time dependence of electrical resistivity while holding at a set temperature of 155 K in the cooling process of the fourth cycle.
Figure 2. Time dependence of electrical resistivity while holding at the temperatures indicated in Figure 1. The decrease in resistivity in (a and b) is due to the isothermal B2–B190 transformation and the increase in resistivity in (d) is due to the isothermal B190 –B2 transformation.
145, 130, 115 and 100 K. When the specimen is held at 85 K (Fig. 2c), no decrease in resistivity was detected while holding for 3 ks. This result implies that isothermal transformation does not proceed at 85 K. In the third cycle, we performed a continuous cooling process followed by a step heating process. The specimen was cooled to 4.2 K at a rate of 2 K min1; in the heating process, it was held at a set temperature for 3 ks, followed by heating to the next set temperature at a rate of 2 K min1. The set temperatures were 100, 115, 130, 145, 180, 185, 195 and 205 K. The vertical line at 100 and 115 K of the third cycle curve in Figure 1 is due to the progress of the martensitic transformation while holding at these temperatures. Figure 2d shows the time dependence of the resistivity while holding at 195 K in the third cycle. We notice the increase in resistivity while holding at 195 K. This result implies that the B190 –B2 transformation (i.e. the reverse transformation) occurs while holding at this temperature. No clear time dependence was detected at other holding temperatures of the third cycle. By comparing the cooling curves of the first and third cycles, we notice that the peak temperature of resistivity decreases as the number of cycles increases. This implies that the results of the holding experiment depend on the
Figure 4. The time required for a 1% decrease in the electrical resistivity while holding at the set temperatures in the second cycle. The open circles means the decrease in resistivity is <1% for the maximum holding time of 3 ks. The dotted line is a visual guide.
number of thermal cycles. Presumably, defects introduced during thermal cycling are responsible for the decrease in Ms as discussed by L’vov et al. [18]. Considering the influence of the thermal cycling, we performed a holding experiment again at 155 K during the cooling process of the fourth cycle. The result of this holding is shown in Figure 3; the temperature of the stage, on which the specimen is mounted, is also shown. We notice that the resistivity starts to decrease after an incubation time of about 3 ks. This result is slightly different from the holding experiment at the same temperature of the second cycle (Fig. 2b), where a clear incubation time was not detected. Presumably, the Ms temperature of the second cycle is above 155 K, while Ms of the fourth cycle is below 155 K. From the holding experiment of the second cycle, we plotted the time corresponding to the 1% decrease in electrical resistivity (see Fig. 4). The change in resistivity implies an increase in the fraction of the B190 phase. We notice there is a nose near 130 K. This result implies that the B2–B190 transformation most easily proceeds near 130 K.
T. Fukuda et al. / Scripta Materialia 68 (2013) 984–987
In summary, we investigated time dependence of the B2–B190 transformation in Ti–51.2Ni alloy, and detected an incubation time of the transformation. We also a detected time dependence of the reverse transformation. A C-curve with a nose located near 130 K is expected to appear in the TTT diagram of the B2–B190 transformation. A part of the present work was supported by the Global COE Program “Center of Excellence for Advanced Structural and Functional Materials Design” from MEXT and by Grand-in-Aid for Scientific Research (Kibanb:23360280) from JSPS. [1] Z. Nishiyama, in: M.E. Fine, M. Meshii, C.M. Wayman (Eds.), Martensitic Transformations, Academic Press, New York, 1978. [2] N.N. Thadhani, M.A. Meyers, Prog. Mater. Sci. 30 (1986) 1. [3] G.V. Kurdiumov, Dokl Akad Nauk SSSR 60 (1948) 1548. [4] T. Kakeshita, T. Saburi, K. Kindo, S. Endo, Phase Transitions 70 (1999) 65. [5] T. Kakeshita, T. Takeguchi, T. Fukuda, T. Saburi, Mater. Trans. JIM 37 (1996) 299.
987
[6] Y.-h. Lee, M. Todai, T. Okuyama, T. Fukuda, T. Kakeshita, R. Kainuma, Scripta Mater. 64 (2011) 927. [7] A. Planes, F.-J. Pe´rez-Reche, E. Vives, L. Man˜osa, Scripta Mater. 50 (2004) 181. [8] V.K. Sharma, M.K. Chattopadhyay, S.B. Roy, Phys. Rev. B 76 (2007) 140401. [9] W. Ito, R.Y. Umetsu, R. Kainuma, T. Kakeshita, K. Ishida, Scripta Mater. 63 (2010) 73. [10] S. Kustov, I. Golovin, M.L. Corro´, E. Cesari, J. Appl. Phys. 107 (2010) 053525. [11] F. Chen, Y.X. Tong, B. Tian, Y.F. Zheng, Y. Liu, Intermetallics 18 (2010) 188. [12] P.J. Shamberger, A.B. Pakhomov, F.S. Ohuchi, MRS Proc. 1200 (2010) 65. [13] C. Hu¨rrich, S. Roth, M. Po¨tschke, B. Rellinghaus, L. Schultz, J. Alloys Compd. 494 (2010) 40. [14] K. Otsuka, X. Ren, T. Takeda, Scripta Mater. 45 (2001) 145. [15] S. Kustov, D. Salas, E. Cesari, R. Santamarta, J.V. Humbeeck, Acta Metall. 60 (2012) 2578. [16] W. Tang, Metall. Trans. A 28 (1997) 537. [17] J.I. Kim, Y. Liu, S. Miyazaki, Acta Mater. 52 (2004) 487. [18] V.A. L’vov, A. Kosogor, J.M. Barandiaran, V.A. Chernenko, Acta Mater. 60 (2012) 1587.
Scripta Materialia 68 (2013) 984–987 www.elsevier.com/locate/scriptamat
Isothermal nature of the B2–B190 martensitic transformation in a Ti–51.2Ni (at.%) alloy Takashi Fukuda,⇑ Shinji Yoshida and Tomoyuki Kakeshita Department of Materials Science and Engineering, Graduate School of Engineering, Osaka University, 2-1, Yamada-oka, Suita, Osaka 565-0871, Japan Received 5 February 2013; revised 25 February 2013; accepted 26 February 2013 Available online 14 March 2013
The B2–B190 transformation in Ti–51.2Ni (at.%) alloy exhibits a clear time dependence. The transformation starts after an incubation time when the specimen is held above Ms, and proceeds while holding in the temperature range between 160 and 100 K. The nose temperature is expected to be near 130 K. The reverse transformation also shows a clear time dependence. Ó 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Thermal activation; Titanium–nickel alloy; Shape memory alloy; Nucleation
Martensitic transformations (MTs) are frequently classified into two groups, i.e. athermal or isothermal MTs, from the viewpoint of kinetics [1,2]. In an athermal transformation, the volume fraction of the martensite is considered to depend on temperature but not on time. In an isothermal transformation, the volume fraction of the martensite phase depends on both temperature and time. However, we consider that MTs are intrinsically isothermal, and an athermal transformation is a special case of an isothermal transformation as pointed out by Kurdiumov [3]. This interpretation has been supported by several experimental results. For an example, an iron-based alloy exhibiting a clear C-curve in its time– temperature–transformation (TTT) diagram transforms instantaneously when a magnetic field is applied [4]. In addition, an iron-based alloy which has a clear Ms temperature exhibits a C-curve in its TTT diagram when a hydrostatic pressure is applied [4]. These results imply that athermal and isothermal transformations are intrinsically the same in nature. Considering the isothermal nature of MTs, it is expected that a MT should occur even above the Ms (martensite start temperature) after some incubation time when the specimen is held below the equilibrium temperature T0. This prediction was confirmed to be correct in a Fe–Ni alloy [4], in a Cu–Al–Ni alloy [5] and in
⇑ Corresponding
author. Tel.: +81 6 6879 7483; fax: +81 6 6879 7522.; e-mail: [email protected]
Ni–Co–Mn–In alloy [6]. Moreover, the time dependence of MTs was recently found in many shape memory alloys [7–13]. However, there is an opposing interpretation of the kinetics of martensitic transformation. Otsuka et al. [14] examined the time dependence of the B2–B190 transformation by using a Ti–50Ni (at.%) alloy. They held the specimen for 21 days at a temperature above its Ms, and reported that no change in resistivity was detected. From their result, they concluded that the B2– B190 transformation in Ti–Ni alloy does not depend on time. They considered that the time dependence reported in the Cu–Al–Ni is due to diffusion of atoms while holding near 200 K. Recently, the kinetics of the B2–B190 transformation was re-examined by Kustov et al. [15] for a Ti– 50.2Ni (at.%) alloy. They held the specimen at a temperature in between its Ms and Mf, and reported that the transformation proceeds isothermally while holding at that temperature. However, they were not able to detect a clear incubation time before the martensitic transformation. In addition, they were not able to detect any time dependence for the reverse transformation. Based on this observation, they considered that although the growth process of the B2–B190 transformation depends on time, the nucleation process does not depend on time. We consider that the kinetics of the B2–B190 transformation is the same as that of other MTs. Therefore, an incubation time should exist for the transformation even though detection of this may not be easy. The aim of the
1359-6462/$ - see front matter Ó 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.scriptamat.2013.02.057
T. Fukuda et al. / Scripta Materialia 68 (2013) 984–987
present study is to show the existence of an incubation time for the B2–B190 transformation. We considered that selection of the alloy is crucial to detecting the incubation time for the B2–B190 transformation, i.e. the incubation time will be detected clearly by using an alloy with a low Ms temperature. A clear time dependence of MT was reported in an alloy with low Ms in a Ni45Co5Mn36.5In13.5 alloy [6]. According to previous studies, the Ms temperature of the B2–B190 transformation in binary Ti–Ni alloys decreases nearly linearly with increasing Ni content, and disappears suddenly near a Ni content of 51.5 at.% [16]. By making some preliminary experiments, we selected Ti–51.2Ni (at.%) alloy to investigate the time dependence of the B2–B190 transformation. An ingot of Ti–51.2Ni (at.%) alloy of nominal composition was prepared by an arc melting method. It was remelted several times to ensure homogeneity. The ingot was heat-treated at 1273 K for 24 h in vacuo and quenched into ice water. A specimen for electrical resistivity measurement (10 mm 2 mm 0.3 mm) and a specimen for differential scanning calorimetry (DSC, 3 mm 3 mm 1 mm) were cut from the ingot, and heat-treated at 1273 K in vacuo for 1 h followed by quenching into ice water. The surface of each specimen was electropolished in an electrolyte composed of acetic acid and perchloric acid. The electrical resistivity was measured by a four-probe method with a current of 200 mA and a frequency of 10 Hz. The specimen for the resistivity measurement was mounted on a copper stage using silicone grease, and the temperature of the stage was monitored throughout the measurements. The overshoot and undershoot of the temperature before isothermal holding was within 100 mK, and the fluctuation of the temperature while holding was within 10 mK. The DSC measurement was made in the temperature range between 353 and 123 K with a cooling and heating rate of 5 K min1. The DSC curve of the Ti–51.2Ni alloy exhibited an exothermic peak starting at 156 K in the cooling process and an endothermic peak ending at 215 K in the heating process. The latent heat obtained from the heating curve was 5.2 J g1 (0.28 kJ mol1), and the entropy change was estimated to be about 0.025 J g1 K1. This value is approximately one-half of that of Ti–50.9Ni alloy (0.050 J g1 K1) [17]. This difference suggests that nearly one-half of the specimen does not transform at a cooling rate of 5 K min1. Presumably, the progress of the martensitic transformation is suppressed by the internal stress. The isothermal nature of the B2–B190 transformation has been examined in detail by electrical resistivity measurements. We performed several thermal cycles for the investigation. Since the B2–B190 transformation temperature is known to depend on thermal cycling, the number of thermal cycles after the heat treatment is noted below. Figure 1 shows electrical resistivity curves measured with a cooling and heating rate of 2 K min1. During the cooling process of the first cycle, the resistivity starts to decrease at 154 K. The decrease in resistivity is due to the B2–B190 transformation. During the heating process, the resistivity curves start to deviate from that of
985
Figure 1. Temperature dependence of the electrical resistivity of a Ti– 51.2Ni alloy. The resistivities of the first and third cycles are shifted by +40 and 40 lX cm. Isothermal holding was done at 160, 155, 150, 145, 130, 115, 100 and 85 K in the cooling process of the second cycle and at 100, 115, 130, 145, 180, 185, 195 and 205 K in the heating process of the third cycle.
the cooling curve at 98 K, and then start to decrease with increasing temperature. The decrease in resistivity above 98 K strongly suggests that the B2–B190 transformation proceeds even during the heating process. Then, on further heating, the resistivity starts to increase at 187 K, which is due to the reverse transformation. In the second cycle, we made a step cooling experiment followed by a continuous heating, as reported by Planes et al. [7]. The specimen was cooled to a set temperature at a rate of 2 K min1, and then held at the temperature for 3 ks, followed by cooling to the next set temperature at a rate of 2 K min1. The set temperatures were 160, 155, 150, 145, 130, 115, 100 and 85 K. The vertical line of the resistivity curve in the second cycle is due to the progress of martensitic transformation while holding. Figure 2a–c shows the time dependence of the resistivity of the specimen at representative holding temperatures in the second cycle. When the specimen is held at 160 K (Fig. 2a), which is 6 K higher than the peak temperature of resistivity in the first cycle, the resistivity starts to decrease after a holding time of about 2.5 ks as indicated by an arrow. This result indicates that the B2–B190 transformation initiates after an incubation time of 2.5 ks. The holding temperature of 160 K is expected to be above the Ms of this cycle although we are not sure of the precise Ms temperature of the second cycle. When the specimen is held at 155 K (Fig. 2b), the resistivity starts to decrease as soon as the holding starts, meaning that the transformation occurs without detectable incubation time while holding at 155 K. A similar time dependence of resistivity was observed at 150,
986
T. Fukuda et al. / Scripta Materialia 68 (2013) 984–987
Figure 3. Time dependence of electrical resistivity while holding at a set temperature of 155 K in the cooling process of the fourth cycle.
Figure 2. Time dependence of electrical resistivity while holding at the temperatures indicated in Figure 1. The decrease in resistivity in (a and b) is due to the isothermal B2–B190 transformation and the increase in resistivity in (d) is due to the isothermal B190 –B2 transformation.
145, 130, 115 and 100 K. When the specimen is held at 85 K (Fig. 2c), no decrease in resistivity was detected while holding for 3 ks. This result implies that isothermal transformation does not proceed at 85 K. In the third cycle, we performed a continuous cooling process followed by a step heating process. The specimen was cooled to 4.2 K at a rate of 2 K min1; in the heating process, it was held at a set temperature for 3 ks, followed by heating to the next set temperature at a rate of 2 K min1. The set temperatures were 100, 115, 130, 145, 180, 185, 195 and 205 K. The vertical line at 100 and 115 K of the third cycle curve in Figure 1 is due to the progress of the martensitic transformation while holding at these temperatures. Figure 2d shows the time dependence of the resistivity while holding at 195 K in the third cycle. We notice the increase in resistivity while holding at 195 K. This result implies that the B190 –B2 transformation (i.e. the reverse transformation) occurs while holding at this temperature. No clear time dependence was detected at other holding temperatures of the third cycle. By comparing the cooling curves of the first and third cycles, we notice that the peak temperature of resistivity decreases as the number of cycles increases. This implies that the results of the holding experiment depend on the
Figure 4. The time required for a 1% decrease in the electrical resistivity while holding at the set temperatures in the second cycle. The open circles means the decrease in resistivity is <1% for the maximum holding time of 3 ks. The dotted line is a visual guide.
number of thermal cycles. Presumably, defects introduced during thermal cycling are responsible for the decrease in Ms as discussed by L’vov et al. [18]. Considering the influence of the thermal cycling, we performed a holding experiment again at 155 K during the cooling process of the fourth cycle. The result of this holding is shown in Figure 3; the temperature of the stage, on which the specimen is mounted, is also shown. We notice that the resistivity starts to decrease after an incubation time of about 3 ks. This result is slightly different from the holding experiment at the same temperature of the second cycle (Fig. 2b), where a clear incubation time was not detected. Presumably, the Ms temperature of the second cycle is above 155 K, while Ms of the fourth cycle is below 155 K. From the holding experiment of the second cycle, we plotted the time corresponding to the 1% decrease in electrical resistivity (see Fig. 4). The change in resistivity implies an increase in the fraction of the B190 phase. We notice there is a nose near 130 K. This result implies that the B2–B190 transformation most easily proceeds near 130 K.
T. Fukuda et al. / Scripta Materialia 68 (2013) 984–987
In summary, we investigated time dependence of the B2–B190 transformation in Ti–51.2Ni alloy, and detected an incubation time of the transformation. We also a detected time dependence of the reverse transformation. A C-curve with a nose located near 130 K is expected to appear in the TTT diagram of the B2–B190 transformation. A part of the present work was supported by the Global COE Program “Center of Excellence for Advanced Structural and Functional Materials Design” from MEXT and by Grand-in-Aid for Scientific Research (Kibanb:23360280) from JSPS. [1] Z. Nishiyama, in: M.E. Fine, M. Meshii, C.M. Wayman (Eds.), Martensitic Transformations, Academic Press, New York, 1978. [2] N.N. Thadhani, M.A. Meyers, Prog. Mater. Sci. 30 (1986) 1. [3] G.V. Kurdiumov, Dokl Akad Nauk SSSR 60 (1948) 1548. [4] T. Kakeshita, T. Saburi, K. Kindo, S. Endo, Phase Transitions 70 (1999) 65. [5] T. Kakeshita, T. Takeguchi, T. Fukuda, T. Saburi, Mater. Trans. JIM 37 (1996) 299.
987
[6] Y.-h. Lee, M. Todai, T. Okuyama, T. Fukuda, T. Kakeshita, R. Kainuma, Scripta Mater. 64 (2011) 927. [7] A. Planes, F.-J. Pe´rez-Reche, E. Vives, L. Man˜osa, Scripta Mater. 50 (2004) 181. [8] V.K. Sharma, M.K. Chattopadhyay, S.B. Roy, Phys. Rev. B 76 (2007) 140401. [9] W. Ito, R.Y. Umetsu, R. Kainuma, T. Kakeshita, K. Ishida, Scripta Mater. 63 (2010) 73. [10] S. Kustov, I. Golovin, M.L. Corro´, E. Cesari, J. Appl. Phys. 107 (2010) 053525. [11] F. Chen, Y.X. Tong, B. Tian, Y.F. Zheng, Y. Liu, Intermetallics 18 (2010) 188. [12] P.J. Shamberger, A.B. Pakhomov, F.S. Ohuchi, MRS Proc. 1200 (2010) 65. [13] C. Hu¨rrich, S. Roth, M. Po¨tschke, B. Rellinghaus, L. Schultz, J. Alloys Compd. 494 (2010) 40. [14] K. Otsuka, X. Ren, T. Takeda, Scripta Mater. 45 (2001) 145. [15] S. Kustov, D. Salas, E. Cesari, R. Santamarta, J.V. Humbeeck, Acta Metall. 60 (2012) 2578. [16] W. Tang, Metall. Trans. A 28 (1997) 537. [17] J.I. Kim, Y. Liu, S. Miyazaki, Acta Mater. 52 (2004) 487. [18] V.A. L’vov, A. Kosogor, J.M. Barandiaran, V.A. Chernenko, Acta Mater. 60 (2012) 1587.