The effect of niobium alloying additions on the crystallization of a Fe Si B Nb alloy

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1 Journal of Alloys and Compounds 403 (2005) The effect of niobium alloying additions on the crystallization of a Fe Si B Nb alloy Y.R. Zhang, R.V. Ramanujan School of Materials Science and Engineering, Nanyang Technological University, Singapore , Singapore Received 12 April 2005; received in revised form 14 May 2005; accepted 18 May 2005 Available online 19 July 2005 Abstract The effect of Nb alloying additions on the crystallization behavior of a Fe Si B Nb alloy was studied. The selected alloy compositions are Fe 77.5 Si 13.5 B 9 and Fe 74.5 Si 13.5 B 9 Nb 3. By comparing the crystallization temperatures, activation energy for crystallization, phases and microstructures formed after annealing, the effect of Nb alloying addition in the Fe Si B Nb alloy was determined. It was found that Nb alloying addition changed the crystallization process from primary crystallization in the case of the Fe 77.5 Si 13.5 B 9 alloy to eutectic crystallization in the Fe 74.5 Si 13.5 B 9 Nb 3 alloy. Nb alloying addition also induced complex phase formation including the Fe 23 B 6,Fe 3 B and Fe 3 Si phases. From HRTEM the lattice parameter of the Fe 23 B 6 phase was measured to be nm and the Fe 23 B 6 phase was found to have an ordered fcc structure. Interestingly, Nb alloying addition changed the microstructure from the dendritic morphology in the case of Fe 77.5 Si 13.5 B 9 alloy to equiaxed precipitates in the Fe 74.5 Si 13.5 B 9 Nb 3 alloy. In the case of the Fe 74.5 Si 13.5 B 9 Nb 3 alloy, the morphology showed little change as the annealing time was increased from 30 min to 24 h at 550 C. Nb alloying addition decreased the saturation magnetization Elsevier B.V. All rights reserved. Keywords: Alloying addition; Crystallization; Electron microscopy; Magnetism 1. Introduction The Finemet alloy, with a composition of Fe 73.5 Si 13.5 B 9 Nb 3 Cu 1, exhibits good magnetic properties. The microstructure of this alloy consists of a high density of nanometer sized soft magnetic precipitates of -Fe(Si) within an amorphous matrix. There have been many reports about the crystallization mechanism of this alloy and the crucial role of Nb in this alloy [1 6]. One model has suggested that the effect of the alloying element Nb in this alloy is due to the rejection of Nb atoms during crystallization from the matrix. The rejected Nb atoms can form a diffusion layer with a concentration gradient around the precipitate, which hinders the diffusion of Fe and Si atoms, reducing the growth rate, leading to the formation of nanocrystals [4 6]. A different model has suggested that soft impingement by overlapping fields surrounding the precipitates leads to retardation of crystal growth [7]. These Corresponding author. address: ramanujan@ntu.edu.sg (R.V. Ramanujan). studies on Fe 73.5 Si 13.5 B 9 Nb 3 Cu 1 alloys were carried out in alloys containing both Cu and Nb alloying additions. It is well known that both Cu and Nb will individually influence the thermodynamics and kinetics of the crystallization in Finemet alloy. Hence, in order to obtain a fundamental understanding of the individual effects of Cu and Nb alloying additions in Finemet alloy particular attention should be paid to the influence of separate additions of Cu and Nb to the reference Fe Si B alloy. For the Fe 74.5 Si 13.5 B 9 Nb 3 alloy earlier work has been carried out to study the thermal properties and phase formation [8 14]. However, due to the complex phases formed after crystallization in the Fe Si B Nb alloy detailed microstructural observations and corresponding SADP analysis by TEM have not been reported so far. The present study provides information about phase formation and microstructural observation during the crystallization of the Fe 74.5 Si 13.5 B 9 Nb 3 alloy by DSC, VSM, TEM and XRD techniques. This study provides a reference to understand the effect of Nb alloying addition in Finemet alloys which contain both Cu and Nb /$ see front matter 2005 Elsevier B.V. All rights reserved. doi: /j.jallcom

2 198 Y.R. Zhang, R.V. Ramanujan / Journal of Alloys and Compounds 403 (2005) In the present work two alloy compositions: Fe 77.5 Si 13.5 B 9 and Fe 74.5 Si 13.5 B 9 Nb 3 were selected based on the Finemet alloy composition (Fe 73.5 Si 13.5 B 9 Nb 3 Cu 1 ). The thermal behavior, phase formation, microstructural observations and magnetic properties after heat treatment were obtained by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometery (VSM). 2. Experimental procedure Fe 77.5 Si 13.5 B 9 and Fe 74.5 Si 13.5 B 9 Nb 3 alloys were prepared in the form of 20 m thick and 25 mm wide ribbon, both alloys are amorphous in the as received condition. A NETZSCH DSC-404C was employed for calorimetry. All the DSC experiments were performed in vacuum using ceramic sample pans, the sample weight was about 10 mg. X-ray diffraction studies were carried out in a RIGAKU DMAX 2200 with Cu K radiation. Heat treatment conditions were selected according to the DSC results: both alloys were annealed at 550 C for 5 min, 30 min, 1 h, 4 h, 8 h, 16 h and 24 h in a vacuum furnace (10 5 Torr). A JEOL 2010 Transmission Electron Microscope (TEM) with an accelerating voltage of 200 kv was employed. The samples prepared for TEM observation were cut into 3 mm discs before heattreatment and subsequently ion-milled. Measurements of the magnetic properties were made using a LakeShore 7300 vibrating sample magnetometer. All the measurements were conducted three times to minimize errors. 3. Results By means of DSC the crystallization temperatures of the selected alloys were measured at heating rates of 5, 10 and 20 K/min, as shown in Fig. 1(a and b). The corresponding exothermic effects for both alloys are provided in Table 1(a and b). Fig. 1(a and b) show the DSC data obtained at different heating rates: 5, 10 and 20 K/min, respectively, for the initially amorphous Fe Si B and Fe Si B Nb alloys. At a heating rate of 10 K/min, the DSC curve for the Fe Si B alloy showed two exothermic peaks at about and C, however the Nb containing alloy exhibited only one exothermic peak at a higher temperature of C. In the Fe Si B alloy, as the heating rate increased from 5 to 20 K/min the peak become sharper while with Nb alloying addition the peak is highest at the heating rate of 10 K/min. By using the Doyle Ozawa Method the activation energies of different alloys can be calculated by means of the following Table 1 The temperatures corresponding to the exothermic peaks for (a) the Fe Si B alloy and (b) the Fe Si B Nb alloy Heating rate (K/min) Fig. 1. (a) DSC results for the Fe Si B alloy at heating rates of: (1) 5 K/min, (2) 10 K/min and (3) 20 K/min. (b) DSC results for the Fe Si B Nb alloy at heating rates of: (1) 5 K/min, (2) 10 K/min and (3) 20 K/min (a) The Fe Si B alloy First peak T x1 ( C) T p1 ( C) T e1 ( C) H (J/g) Second peak T x2 ( C) T p2 ( C) T e2 ( C) H (J/g) (b) The Fe Si B Nb alloy First peak T x ( C) T p ( C) T e ( C) H (J/g) T x : the onset temperature of the crystallization; T p : the peak temperature of the crystallization; T e : the ending temperature of the crystallization; H: the enthalpy of the whole crystallization process.

3 Y.R. Zhang, R.V. Ramanujan / Journal of Alloys and Compounds 403 (2005) equation [15]: [ ] AE Log b = Log E RF(α) RT where b is the heating rate, A a constant, F(α) the crystallized fraction, T the temperature corresponding to the crystallized fraction, E the activation energy and R is the Boltzmann constant. Plotting Log b on the Y-axis and 1/T on the X- axis a straight line can be obtained, the slope of which is E/R, thus the activation energy can be calculated (Figs. 2 and 3 and Table 2). In the case of the Fe Si B alloy, the values of the activation energy for the first crystallization peak and second peak are 376 kj/mol and 342 kj/mol, respectively. In the Fe Si B Nb alloy, the activation energy is 421 kj/mol for the single peak. This indicated that Nb alloying additions stabilized the amorphous matrix which is consistent with earlier reports [12,16,17]. Phase formation following primary crystallization for both alloys was identified from the XRD data and the results are shown in Figs. 4 and 5 for the Fe Si B and the Fe Si B Nb alloy, respectively. From Figs. 4 and 5 it was observed that both alloys were still amorphous after heat treatment at 550 C for 5 min. Crystallization occurred after annealing for 30 min. For the Fe Si B alloy, the Fe 3 Si phase dominated during the primary crystallization until 4 h when the Fe 3 B phase was identified, which indicated the initiation of secondary crystallization (Fig. 4). After the annealing was conducted for 16 h the Fe 2 B phase was observed, it was formed by the decomposition of the Fe 3 B phase. With Nb alloying addition complex Fe 23 B 6 and Fe 3 B phases were induced in addition to the Fe 3 Si phase (Fig. 5). It was also observed that as the annealing time was increased the relative intensity of highest peak of the Fe 3 Si phase to that of the Fe 23 B 6 phase increased. However, the relative intensity of the highest peak of the Fe 3 B to that of the Fe 23 B 6 decreased as the annealing time was increased. Transmission electron microscopy (TEM) can provide more information about the microstructural evolution during crystallization. In the case of the Fe Si B alloy, a dendritic morphology of the Fe 3 Si phase was observed when the annealing was conducted at 550 C for 30 min (Fig. 6). However, with Nb alloying additions, instead of the dendritic morphology, the various phases formed in an equiaxed morphology (Fig. 7). Interestingly, as the annealing time was increased from 30 min to 24 h the microstructure showed little change (Fig. 7). TEM observations of the phases in the Fig. 2. Activation energy obtained from DSC measurement for (a) the first peak and (b) second crystallization peak for a Fe 77.5 Si 13.5 B 9 alloy. Nb containing alloy are shown in Figs A high resolution TEM micrograph and corresponding SADP of the Fe 23 B 6 phase are shown in Fig. 8. The lattice parameter of the Fe 23 B 6 was measured as nm, SADP analysis indicated an ordered fcc phase. For the Fe 3 B phase a twinned lamellar morphology was observed in BF and DF micrographs, the corresponding SADP is provided in Fig. 9. BF, DF micrographs of the morphology of the Fe 3 Si phase and corresponding SADP are shown in Fig. 10. Instead of the dendritic Table 2 Calculated activation energy of crystallization for the selected alloys Fe 74.5 Nb 3 Si 13.5 B 9 Fe 77.5 Si 13.5 B 9 5 K/min a 10 K/min a 20 K/min a 5 K/min a 10 K/min a 20 K/min a First peak ( C) Activation energy (kj/mol) Second peak ( C) Activation energy (kj/mol) 342 a Heating rate.

4 200 Y.R. Zhang, R.V. Ramanujan / Journal of Alloys and Compounds 403 (2005) Fig. 3. Activation energy obtained from DSC measurement for the only peak of Fe 74.5 Si 13.5 B 9 Nb 3. Fig. 5. XRD results for the Fe Si B Nb alloy heat treatment at 550 C for different holding time: (1) 5 min, (2) 30 min, (3) 1 h, (4) 4 h, (5) 8 h, (6) 16 h and (7) 24 h: Fe 3 Si ( ), Fe 23 B 6 ( ) and Fe 3 B( ). morphology in Fe Si B alloy, a spheroidal microstructure was observed. The magnetic properties of coercivity and saturation magnetization were measured by VSM. The results are shown in Figs. 11 and 12. The magnetization and coercivity of the received amorphous Fe Si B alloy are 1.3 T and 40 A/m. In the case of the Fe Si B Nb alloy, the saturation magnetization of the as-received amorphous alloys are 1.2 T and 500 A/m. For the Fe Si B alloy magnetization reached the highest value of 1.7 T after annealing at 550 C for 1 h while the coercivity reached the highest value of 5000 A/m at 550 C for 4 h. With Nb alloying addition the magnetization was reduced compared with the corresponding value in the Fe Si B alloy for the same annealing conditions. In Fig. 6. BF TEM micrograph of Fe Si B alloy heat treatment at 550 C for 30 min. the case of the Fe Si B Nb alloy, as the annealing time was increased from 1 h to 24 h, the magnetization increased to the highest value of 1.6 T at 550 C for 24 h, while the coercivity remains about 1000 A/m. 4. Discussion 4.1. Thermal properties Fig. 4. XRD results for the Fe Si B alloy heat treatment at 550 C for different holding time: (1) 5 min, (2) 30 min, (3) 1 h, (4) 4 h, (5) 8 h, (6) 16 h and (7) 24 h: Fe 3 Si ( ), Fe 2 B( ) and Fe 3 B( ). For the Fe Si B alloy the DSC curve exhibits two exothermic peaks which means that there exists a two step crystallization processes before the final stable phases are obtained. The first peak represents the formation of the Fe 3 Si phase and the

5 Y.R. Zhang, R.V. Ramanujan / Journal of Alloys and Compounds 403 (2005) Fig. 7. BF TEM micrograph of the Fe Si B Nb alloy annealed at 550 C for different time: (a) 30 min and (b) 24 h. second peak indicates the appearance of the Fe 3 B compound, this interpretation is supported by the XRD data (Fig. 4). On the other hand, with Nb alloying addition only one peak was obtained in the DSC curves which is consistent with a previous report that the range of the coexistence of the Fe 3 Si phase and the amorphous matrix was reduced by the addition of Nb and disappears with 3 at% Nb in the Fe Si B alloy [16]. However, the single peak in the DSC curve obtained in this investigation is different from the observation of two peaks reported by Yavari and Negri [6] and Mattern et al. [17]. Our results indicated that Nb alloying addition in the Fe Si B alloy altered the thermodynamics of the crystallization process. Nb alloying addition changed the crystallization mechanism from primary crystallization in the case of the Fe Si B alloy to eutectic crystallization of Fe 3 B and Fe 23 B 6 phases in the Fe Si B Nb alloy. Regarding the crystallization temperature measured by DSC, it has been reported earlier that Nb concentration influences the onset of crystallization [19]. When 3 at% Nb was added to the Fe Si B alloy, the peak shifts from Cin the case of the Fe Si B alloy to C in the Fe Si B Nb alloy, which is consistent with the theory that in glasses of the type Fe M B Si (where M is selected from a large number of metals) T x is increased when the atomic size of M is larger than that of iron and decreased when it is smaller [18]. The higher T x indicates that Nb stabilizes the glassy phase and made it difficult to crystallize, consistent with the previous report [16,19]. This can also be observed from the calculated activation energy, the activation energy of the Fe Si B alloy is about 376 kj/mol while that of the Fe Si B Nb alloy is 421 kj/mol. In addition, the single peak is sharp and narrow, thus the crystallization process of the alloy containing Nb is difficult to control once it has begun. Fig. 8. HRTEM micrograph of the precipitate of the Fe 23 B 6 phase of the Fe Si B Nb alloy annealed at 550 C for 30 min: (a) bright field image and (b) SADP, zone axis: [0 1 1] Crystallization process of the Fe Si B Nb alloy From the XRD results it was observed that the Fe 3 Si phase dominated as the crystallization proceeded in the case

6 202 Y.R. Zhang, R.V. Ramanujan / Journal of Alloys and Compounds 403 (2005) Fig. 9. TEM micrograph of the Fe 3 B phase of the Fe Si B Nb alloy annealed at 550 C for 30 min: (a) bright field image, (b) dark field image and (c) SADP, zone axis: [1 2 2]. of Fe Si B alloy while with Nb alloying addition, in addition to the Fe 3 Si phase, the Fe 23 B 6 and Fe 3 B phases were formed (Figs. 4 and 5). This is because the Nb alloying addition changed the crystallization mechanism from the primary crystallization into eutectic crystallization. This is supported by the DSC results: there is only one peak in the DSC curve of the Fe Si B Nb alloy, as compared to the observed two peaks in the DSC curve of the Fe Si B alloy. From the XRD data of the amorphous alloy Nb alloying addition resulted in an appreciable broadening of the diffraction maximum. Thus, addition of Nb increased the topological disorder in the amorphous structure, as has been reported earlier [20]. A greater number of phases were formed with Nb alloying addition, the morphology after crystallization was also dramatically different. In the case of the Fe Si B alloy, a dendritic morphology was observed after primary crystallization at 550 C for 30 min (Fig. 6). However equiaxed crystals were observed in the Fe Si B Nb alloy. It has been reported by Kulik and Gupta et al. that for the Fe Si B and the other related alloy compositions different heating rates lead to different morphologies of the crystallization products [8,13, 21 25]. Specifically while heating at slow rates produced the dendritic morphology, fast heating rates produced a fine nanocrystalline structure. The nucleation rate was enhanced and the growth rate was decreased at faster heating rates (Fig. 13). At the small crystal size produced by fast heating rate a compact equiaxed structure was observed. Kulik suggested that at small crystal size the equiaxed morphology is favored, beyond a critical size interfacial stability develops resulting in a dendritic structure. We have also observed this phenomenon by in situ hot stage TEM [26]. A similar phenomenon can account for the morphology of Nb containing alloys, in which a small size of equiaxed crystals was observed compared with dendritic morphology of the Nb-free alloys. By reducing the growth rate due to Nb additions, a smaller crystal size is obtained which leads to an equiaxed morphology. In the Fe Si B Nb alloy Nb alloying addition reduced growth rate which is helpful for the suppression of the supercooling resulting in the dendrtic morphology. In order to avoid the constitutional supercooling the following condition

7 Y.R. Zhang, R.V. Ramanujan / Journal of Alloys and Compounds 403 (2005) Fig. 10. TEM micrograph of the Fe 3 Si phase of the Fe Si B Nb alloy annealed at 550 C for 30 min: (a) bright field image, (b) dark field image and (c) SADP, zone axis: [0 1 1]. should be reached [27]: T l v > T 1 T 3 D (1) stands for the temperature gradient at the interface between the matrix and the precipitate as the crystallization began; T 1 T 3 is the temperature difference between the matrix and the precipitate after crystallization is com- T l Fig. 11. Magnetization dependence on annealing time at 550 C. Fig. 12. Coercivity dependence on annealing time at 550 C.

8 204 Y.R. Zhang, R.V. Ramanujan / Journal of Alloys and Compounds 403 (2005) increased as the annealing time was increased from 30 min to 24 h Magnetic properties Fig. 13. Schematic diagram of the annealing temperature and heating rate dependence of nucleation rate I and growth rate U. pleted; D is the diffusivity in the matrix; v is the growth rate. With Nb alloying addition growth rate (v) was reduced greatly. Crystallization occurred at higher temperature thus the diffusivity in the matrix (D) was higher in the Fe Si B Nb alloy compared with that in the Fe Si B alloy. On the other hand T l and T 1 T 3 remain almost the same. Hence, the decrease of v and the increase of D facilitate the suppression of constitutional supercooling; thus, instead of dendritic morphology in the Fe Si B alloy, the equiaxed morphology was observed in the case of the Fe Si B Nb alloy (Fig. 7). As the annealing time was increased from 30 min to 24 h the microstructure showed little change unlike the usual case of eutectic crystallization in which the growth rate of a crystal is independent of time (until hard impingement with another crystal occurs) [28]. It has been reported earlier that Nb appeared to induce the formation of the Fe 23 B 6 phase when the amorphous phase is crystallized [29], however, these reports mainly deal with phase identification by XRD techniques, no TEM analysis and microstructural observations were reported. Our HRTEM observation of the Fe 23 B 6 phase (Fig. 8) suggests that the lattice parameter has a higher value of nm compared with the value of nm reported by Chen and Ryder which may be due to the presence of Nb atoms [30]. The Fe 23 B 6 phase was found to possess an ordered fcc structure, Chen and Ryder [30] and Inoue and Takeuchi [31] have suggested a disordered fcc structure for this phase. The Fe 3 B phase with a lenticular morphology and the corresponding SADP analysis are shown in Fig. 9. The bcc Fe 3 Si phase formed at the edge of the specimen (Fig. 10). At the edge of the specimen diffusion of elements is faster and the formation of the Fe 3 Si is diffusion controlled thus the Fe 3 Si phase intend to appear at the thinner part of the specimen. The volume fraction of the Fe 3 Si phase was found to increase with annealing time suggested by the XRD results, since the relative intensity of the highest peak of the Fe 3 Si to that of the Fe 23 B 6 phase Niobium alloying addition not only had a large effect on the crystallization temperature, activation energy of crystallization and microstructural evolution during the crystallization, it also affected the magnetic properties. The saturation magnetization and the coercivity after the selected alloys were heat treated at 550 C from 5 min to 24 h were measured by VSM (Figs. 11 and 12). In the case of the Fe Si B alloy, as the annealing time was increased to 1 h the saturation magnetization reached the maximum value of 1.7 T due to the increase of the soft magnetic Fe 3 Si phase. As the annealing time was increased to 4 h the saturation magnetization decreased dramatically to 1.2 T, correspondingly the coercivity increased from 3 ka/m for 1 h to 5 ka/m for 4 h due to the formation of the Fe 3 B phase. As the crystallization proceeded to 24 h the saturation magnetization increased to 1.6 T while the coercivity remains roughly constant. With Nb alloying addition saturation magnetization was reduced compared with the corresponding value of the Fe Si B alloy for the same annealing condition. Regarding to the soft magnetic properties of the Fe 23 B 6 phase there are contrary reports. Hono and Ping suggested that the Fe 23 B 6 phase is a soft magnetic phase and its formation does not adversely affect the magnetic properties [32]. However, Pandaa et al. assumed that the Fe 23 B 6 phase has high magnetocrystalline energy resulting in a degradation in soft magnetic properties [33]. As the annealing time was increased from 1 to 4 h the saturation magnetization decreased sharply due to the decreased volume fraction of the soft magnetic Fe 23 B 6 phase although the soft magnetic Fe 3 Si phase increased which can be observed in the XRD data (Fig. 5), which is consistent with the Fe 23 B 6 phase being a soft magnetic phase. 5. Conclusions The effect of Nb alloying addition in the Fe Si B alloys was studied by DSC, XRD, TEM and VSM techniques. Combining the results obtained the following conclusions can be drawn: 1. The DSC results show two distinct exothermic peaks in the Fe Si B alloy, however, only one peak is observed in the Fe Si B Nb alloy. 2. The crystallization temperature at the heating rate of 10 K/min increased from C in the Fe Si B alloy to C of the Fe Si B Nb alloy. Nb alloying addition increased the activation energy of crystallization from 376 kj/mol to 421 kj/mol 3. After heat treatment, it was found from the XRD, TEM and HRTEM results that Nb alloying additions induced

9 Y.R. Zhang, R.V. Ramanujan / Journal of Alloys and Compounds 403 (2005) the formation of the Fe 23 B 6, Fe 3 B phases which were not observed in the Nb free alloys. 4. Significantly, the TEM observations showed that with Nb alloying additions the microstructure after crystallization was dramatically different from that of the Fe Si B alloy. No dendritic microstructure was observed, instead, heterogeneous nucleation and growth of equiaxed crystals was observed in the case of the Fe Si B Nb alloy. 5. The lattice parameter of the Fe 23 B 6 phase was measured as nm and the Fe 23 B 6 phase was indexed as an ordered fcc structure. 6. The alloying addition of Nb decreased the saturation magnetization compared with the corresponding value of the Nb free alloy for the same annealing condition. Acknowledgement The ribbons used in this study were kindly supplied by Dr. Y. Yoshizawa of Hitachi Metal in Japan. References [1] Y. Yoshizawa, S. Oguma, K. Yamaguchi, J. Appl. Phys. 64 (1988) [2] K. Hono, D.H. Ping, M. Ohnuma, H. Onodera, Acta Mater. 47 (1999) 997. [3] J.D. Ayers, V.G. Harris, J.A. Spague, W.T. Elam, H.N. Jones, Acta Metall. 46 (1998) [4] A. Hernando, M. Va zquez, T. Kulik, C. Prados, Phys. Rev. B 51 (1995) [5] K. Hono, D.H. Ping, Mater. Sci. Forum. 307 (1999) 69. [6] A.R. Yavari, D. Negri, Nano Mater. 8 (1997) 969. [7] J.S. Blazquez, V. Franco, A. Conde, J. Phys. Condens. Mater. 14 (2002) [8] T. Kulik, Mater. Sci. Eng. A 159 (1992) 95. [9] T.H. Noh, M.B. Lee, H.J. Jim, I.K. Kang, J. Appl. Phys. 67 (1990) [10] F. Zhou, K.Y. He, M.L. Sui, Mater. Sci. Eng. A181 A182 (1994) [11] I. Mat ko, P. Duhaj, P. Svec, D. Janickovic, Mater. Sci. Eng. A179 A180 (1994) 557. [12] S.D. Kaloshikin, I.A. Tomilin, B.V. Jalnin, I.B. Kekalo, E.V. Shelekhov, Mater. Sci. Forum (1995) 557. [13] T. Kulik, J. Non-Cryst. Solids 287 (2001) 145. [14] P. Duhaj, I. Matko, P. Svec, D. Janickovic, J. Non-Cryst. Solids (1995) [15] T. Ozawa, J. Therm. Anal. 2 (1970) 301. [16] N. Mattern, A. Danzig, M. Muller, Mater. Sci. Forum (1995) 539. [17] N. Mattern, A. Danzig, M. Muller, Mater. Sci. Eng. A. 194 (1995) 77. [18] I.W. Donald, K.D. Ward, H.A. Davies, J.C. Crangle, in: T. Masumoto, K. Suzuki (Eds.), Proceedings of the Fourth International Conference on Rapidly Quenched Metals, Japan Institute of Metals, Sendai, [19] P. Marin, M. Vazquez, A.O. Olofinjana, H.A. Davies, Nano Mater. 10 (1998) 299. [20] A. Gupta, S.N. Kane, N. Bhagat, T. Kulik, J. Magn. Magn. Mater (2005) 492. [21] T. Kulik, Mater. Sci. Forum (1997) 421. [22] T. Kulik, T. Horuba, H. Matyja, Mater. Sci. Eng. A 157 (1992) 107. [23] T. Kulik, D. Bucka, H. Matyja, J. Mater. Sci. Lett. 12 (1993) 76. [24] T. Kulik, Mater. Sci. Forum (1998) 707. [25] A. Gupta, S.N. Kane, N. Bhagat, T. Kulik, J. Magn. Magn. Mater (2003) 492. [26] Y.R. Zhang, Y.L. Foo, R.V. Ramanujan, in preparation. [27] D.A. Porter, K.E. Easterling, Phase Transformation in Metals and Alloys, Chapman and Hall, London, 1992, p [28] F.E. Luborsky, Amorphous Metallic Alloys, Butterworths, London, 1983, p. P155. [29] D.H. Ping, K. Hono, H. Kanekiyo, S. Hirosawa, Acta Mater. 47 (1999) [30] W.Z. Chen, P.L. Ryder, Mater. Sci. Eng. B 49 (1997) 14. [31] A. Inoue, A. Takeuchi, Mater. Sci. Eng. A (2004) 16. [32] K. Hono, D.H. Ping, Mater. Sci. Eng. A (2001) 81. [33] A.K. Pandaa, B. Ravikumara, S. Basub, A. Mitraa, J. Magn. Magn. Mater. 260 (2003) 70.